• TABLE OF CONTENTS
HIDE
 Copyright
 Title Page
 Table of Contents
 Introduction
 Dried citrus pulp
 Citrus Molasses
 Citrus peel oils
 Flavonoids
 Citrus seed oils
 Pectic substances
 Food products
 Fermentation products
 Waste disposal
 Acknowledgement
 Literature cited






Group Title: Florid Agriculture Experiment Station bulletin 698
Title: By-products of Florida citrus
CITATION PAGE IMAGE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026803/00001
 Material Information
Title: By-products of Florida citrus composition, technology, and utilization
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 74, 1 p. : ill., charts ; 23 cm.
Language: English
Creator: Hendrickson, Rudolph
Kesterson, J. W
Publisher: Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1965
 Subjects
Subject: Citrus fruits -- By-products -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 70-75.
Statement of Responsibility: R. Hendrickson and J.W. Kesterson.
General Note: Cover title.
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00026803
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 001595740
oclc - 18361874
notis - AHL9835

Table of Contents
    Copyright
        Copyright
    Title Page
        Page 1
    Table of Contents
        Page 2
    Introduction
        Page 3
        Historical
            Page 3
            Page 4
        Purpose
            Page 5
            Page 6
    Dried citrus pulp
        Page 7
        Processing procedure
            Page 7
            Page 8
            Page 9
            Page 10
            Page 11
            Page 12
        Processing variables
            Page 13
            Page 14
            Page 15
            Page 16
            Page 17
            Page 18
            Page 19
        Utilization
            Page 20
    Citrus Molasses
        Page 20
        Processing procedure
            Page 21
            Page 22
        Processing considerations
            Page 23
        Utilization
            Page 24
    Citrus peel oils
        Page 25
        Processing procedure
            Page 25
            Page 26
            Page 27
            Page 28
        Coldpressed citrus oils
            Page 29
            Page 30
            Page 31
            Page 32
            Page 33
        Distilled citrus oils
            Page 34
        Citrus stripper oil
            Page 35
        Utilization
            Page 35
            Page 36
            Page 37
            Page 38
    Flavonoids
        Page 39
        Hesperidin
            Page 40
            Page 41
        Naringin
            Page 42
            Page 43
        Miscellaneous
            Page 44
    Citrus seed oils
        Page 44
        Processing procedure
            Page 45
            Page 46
        Chemical composition
            Page 47
            Page 48
            Page 49
            Page 50
            Page 51
        Utilization of citrus seed oil, meal, and hulls
            Page 52
    Pectic substances
        Page 53
        Page 54
        Pectic pomace
            Page 55
        Juice sacs other products
            Page 55
        Utilization
            Page 56
    Food products
        Page 56
        Brined and candied peel
            Page 56
        Marmalades
            Page 57
        Bland syrup
            Page 58
            Page 59
        Peel seasoning
            Page 60
    Fermentation products
        Page 60
        Vinegar
            Page 60
        Feed yeast
            Page 61
        Citric and lactic acid
            Page 62
            Page 63
        Butylene glycol, 2-3
            Page 64
        Wines, brandies, and citrus alcohol
            Page 64
            Page 65
    Waste disposal
        Page 66
        Methods of disposal
            Page 67
        Biological treatment
            Page 67
            Page 68
    Acknowledgement
        Page 69
    Literature cited
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
Full Text


DIGITIZATION PERMISSION

[year of pubhcation] Florida Museum of Natural History [source text]

The Florida Museum of Natural History, formerly the Florda State
Museum, holds all nghts to the source text of ths electronic resource on
behalf ofthe State of Flonda The Flonda Museum of Natural History shall
be considered the copyrght holder for the text and images of this
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Under the Statutes of Flonda (FS 25705, 257 105, and 377 075), the Flonda
Museum of Natural History (Ganesville, FL) publisher of the Bulletin of the
Flonda State Museum, as a division of state government makes its
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The Flonda Museum of Natural History reserves all nghts to this
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United States of Amenca copynght legislation (U S Code, Title 17, Section
107), are restricted Contact the Flonda Museum of Natural History, a
division of the Unversity of Flonda, i Gamesville, Flonda, for additional
information and permission




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CONTENTS


INTRODUCTION
Historical _-
Purp se ------- ----- -- ---- --------------------------------------
Purpose __-~
DRIED CITRUS PULP -- __- _-
Processing Procedure _~__ _
Processing Variables ----_ ---
Utilization ---.. ---.._-___.__ .___.
CITRUS MOLASSES ------_ ---
Processing Procedure _-__......----------.__----
Processing Considerations -_- __
Utilization --_____.... -----------------
CITRUS PEEL OILS ---__--.-----
Method of Commercial Manufacture --------.
Coldpressed Citrus Oils ------------.....----
Distilled Citrus Oils -------------...--
Citrus Stripper Oil --_.------- __ ----
Utilization ---_-----------
FLAVONOIDS --- --------
Hesperidin -..- ---.-----
Naringin -__--_..- ---_. -------..... __._.------.
Miscellaneous --- -----
CITRUS SEED OILS _.... --------------......
Processing Procedure -_-...- __.. -- __
Chemical Composition __- ___ -
Utilization of Citrus Seed Oil, Meal, and Hulls
PECTIC SUBSTANCES .-_ ..--_------_.. ....---
Pectin Pomace _
Juice Sacs and Other Products
Utilization -. ___ _____
FOOD PRODUCTS __------
Brined and Candied Peel -----
Marmalades -. .. ..
Bland Syrup .-------. ---_.--..._............ _-
Peel Seasoning --....._~_-- __.. .-.__.__-....-
FERMENTATION PRODUCTS ----------.-------
Vinegar ----__ __ -_
Feed Yeast -.._ _____._-
Citric and Lactic Acid _
Butylene Glycol, 2-3 -_ ---___
Wines, Brandies, and Citrus Alcohol ___-..--..
WASTE DISPOSAL ........ ---------------
Methods of Disposal __ ---- -
Biological Treatment -. __
ACKNOWLEDGMENTS .- ------_. -.---

LITERATURE CITED ------_ -


SPage
3
.------------ 3
3
5
7
7
----------- 5

.---- -- -- -- -- 7
------------ 7
13
.-- 20

20
.. .. 21
23
-- 24
-- 25
.-- 25
..- 29
-- 34
.--- 35
..... -- 35

-.. 39
40
--- 42
------ .44

--- 44
-__ -- 45
47
52
.-.-. .- 53
55
55
56

56
56
---- 57
----- 58
--..- 60
-----60
60
61
62
-. ... 64
--.-..64

66
67
67

-----. 69
S70


-.i-







BY-PRODUCTS OF FLORIDA CITRUS
R. Hendrickson and J. W. Kesterson1



INTRODUCTION

Although citrus plantings existed in Florida as early as 1579
(20) 2, the rapid growth in citrus production and processing has
occurred only within the last 35 years. The development of
frozen citrus concentrates led to increasingly large quantities
of peel residue for local disposal. The enormous waste prob-
lem which developed, brought about a citrus by-products
industry.
The increasing quantity of oranges produced and processed
in Florida over the past two decades is shown in Fig. 1. In con-
trast, grapefruit production and processing is noted to have re-
mained relatively constant over the same period. The over-all
result has been an increase in citrus peel residue until ap-
proximately 4.5 billion pounds of peel, rag, and seeds were left
for disposal in the 1961-62 season. A minute portion of this
huge quantity of peel residue is shown prior to further process-
ing on the cover. The majority of this waste residue will be
converted to dried citrus pulp and citrus molasses. Production
of these two fundamental by-products over the last 20 years
is presented in Fig. 2. The divergent production trends shown
are related to the economical return from these two products.



Historical
Waste peel residue became a serious disposal problem as
greater quantities of citrus were processed in Florida. This
residue of peel, pulp, and seeds was first dumped on nearby
pastures and fed wet to livestock. Although this was eaten
readily, it fermented and could not be stored. The citrus in-
dustry soon learned to process the larger quantities of available
1Associate Chemist and Chemist, Citrus Experiment Station, Lake Alfred,
Florida.
'Figures in parentheses refer to Literature Cited.







BY-PRODUCTS OF FLORIDA CITRUS
R. Hendrickson and J. W. Kesterson1



INTRODUCTION

Although citrus plantings existed in Florida as early as 1579
(20) 2, the rapid growth in citrus production and processing has
occurred only within the last 35 years. The development of
frozen citrus concentrates led to increasingly large quantities
of peel residue for local disposal. The enormous waste prob-
lem which developed, brought about a citrus by-products
industry.
The increasing quantity of oranges produced and processed
in Florida over the past two decades is shown in Fig. 1. In con-
trast, grapefruit production and processing is noted to have re-
mained relatively constant over the same period. The over-all
result has been an increase in citrus peel residue until ap-
proximately 4.5 billion pounds of peel, rag, and seeds were left
for disposal in the 1961-62 season. A minute portion of this
huge quantity of peel residue is shown prior to further process-
ing on the cover. The majority of this waste residue will be
converted to dried citrus pulp and citrus molasses. Production
of these two fundamental by-products over the last 20 years
is presented in Fig. 2. The divergent production trends shown
are related to the economical return from these two products.



Historical
Waste peel residue became a serious disposal problem as
greater quantities of citrus were processed in Florida. This
residue of peel, pulp, and seeds was first dumped on nearby
pastures and fed wet to livestock. Although this was eaten
readily, it fermented and could not be stored. The citrus in-
dustry soon learned to process the larger quantities of available
1Associate Chemist and Chemist, Citrus Experiment Station, Lake Alfred,
Florida.
'Figures in parentheses refer to Literature Cited.








Florida Agricultural Experiment Stations


I I


0
0o


0
m


o

2


1941 1946 1951 1956 1961 1941 1946 1951 1956 1961
1942 1947 1952 1957 1962 1942 1947 1952 1957 1962
Season


Fig. I.-A bar graph showing the quantity of Florida oranges and grapefruit
processed, as well as total available, at five-year intervals (34).


- 400
c
0


300


o

To 200
o
0
CL


l. 100


SEASONAL PRODUCTION

(5 Year Intervals)


h


I


*- Citrus Pulp


S0-- Molasses



- --------- 0------ 0-------0
S^


1941-42 1946-47 1951-52 1956-57 1961-62
Season
Fig. 2.-A graph showing the production of dried citrus pulp and molasses (23)
five-year intervals.


1-


4







By-Products of Florida Citrus


residue into a dried feed. Today the only citrus waste dumped
in pastures is an occasional lot of cull fruit. The greater portion
of available citrus peel residue is now profitably manufactured
into dried citrus pulp. There is also an abundance of other
by-products recovered from citrus wastes. The historical de-
velopment of the two most prominent citrus by-products-
dried citrus pulp and citrus molasses-follows.
Dried citrus pulp was produced in commercial quantities
as early as 1932 from citrus residues of two canneries in Tampa.
This utilization had been suggested in 1916 by F. Alex McDermott
(128), who had received a Mellon Institute Research Fellowship
to investigate the utilization of cull citrus fruits in Florida.
Actual production of dried citrus pulp was accomplished in
1925 in the laboratories of the Florida Citrus Exchange. Seth S.
Walker made a product that was fed to Jersey cows at the
Agricultural Experiment Station in Gainesville by John M.
Scott (111), who concluded that the product had merit as a
cattle feed. The excellent qualities of dried citrus pulp were
substantiated in a wide range of feeding trials with dairy and
beef cattle by later investigators (5, 16, 26, 77, 88).
Citrus molasses is essentially concentrated press liquor ex-
pelled from waste citrus peel after adding a small amount of
lime. It was first produced commercially in Florida during the
1941-42 canning season. The cured peel residues were pressed
in this early period to avoid charring that too readily occurred
in drying very wet peel mixtures to citrus pulp. The expelled
citrus press liquor was soon recognized as a potentially valuable
by-product if it was concentrated to molasses. Thereby, another
difficult disposal problem was solved. The feeding value of
citrus molasses for cattle and swine was subsequently establish-
ed (12, 15, 22, 25, 76).

Purpose
This bulletin presents information pertinent to the produc-
tion, evaluation, and usage of Florida citrus by-products. The
many citrus by-products discussed, their origin, and the inter-
relationships are summarized by Fig. 3. All products depicted
have been manufactured at least with pilot plant equipment and
represent more than speculation based on laboratory trials.
Besides its informative value, this bulletin should also convince
the reader of the enormous potential value of waste citrus peel.


5














Peel Residue Raw Juice Waste
.. .'.'." i 1MJ .......

Seeds Peel & Membrane Juice Sacs IFinished Juice


Seed Oil] i Peel Oils Press Liquor G 'Orange Flour

Seed Meal I Tangeretin Stripper Oil |HI or D-I


I anaie reel' reei oe

|Pectin Pomace


I r.ITRI I


FRUIT


w



3.

a
a.

m
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a

0
n:


Water


Methane

Activated
Sludge

Yeast


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a.
?2

sa
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cc





?/2
<-~
1
cc
re
3.
o,


Feed
Yeast


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By-Products of Florida Citrus


DRIED CITRUS PULP
The production of dried citrus pulp in Florida occurs usually
within an eight-month period between November and June,
with November and March being the more slack months. The
finished product is standardized, despite being manufactured
from a varying mixture of grapefruit and orange residue. As
with most feeds, citrus pulp is dried to a moisture content of
approximately 8 percent to prevent microbiological spoilage and
spontaneous combustion. Bulk handling of this dried citrus
pulp has been attempted, but adequate storage procedures have
not been devised.
The demand for a continuous year-round supply of citrus
pulp requires the product to be placed in storage, where in-
sects may become a problem. The saw-toothed grain beetle,
Oryzaephilus surinamensis (L.), was found (79) to be the
primary species almost always associated with the coarse pulp,
while the cigarette beetle, Lasioderma serricorne (F.), more
commonly attacked pellets and fine meals. Other insect species
were also found, and control measures recommended were: 1,
thoroughly clean warehouse before moving new material into
storage; 2, apply a residual insecticidal spray to the interior
of the empty warehouse; 3, block-stack all bagged feed; 4,
periodic aerosol applications such as once per week with a
pyrethrin formulation having a synergist such a piperonyl
butoxide; and 5, the tentatively-suggested use of insecticide-
coated multiwalled paper bags. More recently, warehouse con-
trol of insects has been achieved with a wettable malathion
formulation. A 50 ppm residue tolerance has been approved
for this pesticide in dried citrus pulp (33).


Processing Procedure
The cannery residue ejected by citrus fruit extractors is the
raw material for production of dried citrus pulp. Large ton-
nages of this residue are accumulated and held in unprotected
open pits or on cement slabs. One example of open storage is
shown on the cover. The peel residue is moved by slide con-
veyors and elevators to a hammer mill or shredder (Fig. 4),
where high speed rotating hammers or knives cut it into pieces
approximately 1/4 by 3 inch. Lime (calcium hydroxide or cal-
cium oxide) is proportioned on the moving residue as a powder


7







By-Products of Florida Citrus


DRIED CITRUS PULP
The production of dried citrus pulp in Florida occurs usually
within an eight-month period between November and June,
with November and March being the more slack months. The
finished product is standardized, despite being manufactured
from a varying mixture of grapefruit and orange residue. As
with most feeds, citrus pulp is dried to a moisture content of
approximately 8 percent to prevent microbiological spoilage and
spontaneous combustion. Bulk handling of this dried citrus
pulp has been attempted, but adequate storage procedures have
not been devised.
The demand for a continuous year-round supply of citrus
pulp requires the product to be placed in storage, where in-
sects may become a problem. The saw-toothed grain beetle,
Oryzaephilus surinamensis (L.), was found (79) to be the
primary species almost always associated with the coarse pulp,
while the cigarette beetle, Lasioderma serricorne (F.), more
commonly attacked pellets and fine meals. Other insect species
were also found, and control measures recommended were: 1,
thoroughly clean warehouse before moving new material into
storage; 2, apply a residual insecticidal spray to the interior
of the empty warehouse; 3, block-stack all bagged feed; 4,
periodic aerosol applications such as once per week with a
pyrethrin formulation having a synergist such a piperonyl
butoxide; and 5, the tentatively-suggested use of insecticide-
coated multiwalled paper bags. More recently, warehouse con-
trol of insects has been achieved with a wettable malathion
formulation. A 50 ppm residue tolerance has been approved
for this pesticide in dried citrus pulp (33).


Processing Procedure
The cannery residue ejected by citrus fruit extractors is the
raw material for production of dried citrus pulp. Large ton-
nages of this residue are accumulated and held in unprotected
open pits or on cement slabs. One example of open storage is
shown on the cover. The peel residue is moved by slide con-
veyors and elevators to a hammer mill or shredder (Fig. 4),
where high speed rotating hammers or knives cut it into pieces
approximately 1/4 by 3 inch. Lime (calcium hydroxide or cal-
cium oxide) is proportioned on the moving residue as a powder


7





Florida Agricultural Experiment Stations


I'


F,


I


J


I


Fig. 4.-Hammer mill. (Photograph taken at Kuder Citrus Pulp Company,
Lake Alfred.)


~>""" J "^
Or~i-


8


-







By-Products of Florida Citrus


or slurry immediately before, during, or after shredding the
peel. The lime (0.3 to 0.5 percent) and chopped peel are thor-
oughly mixed and continually intermixed in a reaction conveyor
or pug mill. More simply, this is described as a large modified
screw conveyor. Local alkalinity changes the color of the residue
to a rather bright yellow, which disappears slowly to leave a
straw-colored product as the lime reacts with the acidic com-
ponents. Experienced operators are able to judge if the proper
quantity of lime has been added by color, feel, and consistency
of the product or by its ease of pressing. The high local alka-
linity, occurring shortly after the lime addition, brings about
a rapid degrading and demethylation of the pectins in the peel.
Syneresis sets in, bound juices are released, and the free liquid
portion changes to an acidic pH. The mixture becomes more
liquid and much less slimy and is ready for pressing and drying.
Processors using a pug mill allow a minimum of 5 minutes
for the lime to react. When vertical storage bins are used, ap-
proximately 30 minutes of curing time is necessary before
pressing. Continuous mixing encourages rapid curing. This also
eliminates the agglomeration of the chopped peel into unman-
ageable chunks. Today, there are a number of processors who
dry the cured citrus residues directly without pressing.
When limed citrus residue is pressed in the continuous
presses, the moisture content will be reduced ordinarily from
approximately 82 percent to 72 percent. The pressed residue
and press liquor are then processed independently as diagramed
in the flow and material balance shown in Fig. 5.
The cured and pressed residue, containing from 65 to 75
percent moisture, is conveyed to rotating driers, and is dried
to 6 to 8 percent moisture. After being dried, the citrus pulp,
the hot combustion gases, and moisture pass into a cyclone
separator. The dried solids fall onto the wall of the cone,
while the hot gases and moisture exhaust to the atmosphere.
From the separator, the dried pulp passes to a cooler that is
usually a rotating drum with countercurrent air flow. The
dried pulp is divided into three products at this point: the
countercurrent cooling air carries off the fines or dust; a rotary
screen on the lower end of the cooling drum separates the por-
tion called citrus meal; and the material carried through is the
dried citrus pulp. A typical plant might produce 85 percent
dried citrus pulp, 14 percent citrus meal, and 1 percent fines.


9






Florida Agricultural Experiment Stations


1,000 Boxes of Grapefruit
85,000 Lbs.


40,70(
1,393 C


47.9% Juice
a ~ Extractors

0 Lbs. of Juice 52.1%
cases N 2 Cans I


44,300 Lbs. of Peel,Pulp 8 Seeds
81.9% Moisture
8,020 Lbs. of Dry Solids


53.6% Shred, Lime (0.3-0.6%) 46.4%
Cure 8 Press


23,800 Lbs. of Press Cake
76.0% Moisture
5,705 Lbs. of Dry Matter


20,500 Lbs. of Press Liquor
88.7% Moisture
2,315 Lbs. of Dry Matter


35 Lbs of Evaporate 645 Lbs. of Water
Evaporate Steam Distilled in Flash Chamber
17,595 Lbs. Oil ;--
of Water Separated From Evaporate 16,640 Lbs. of Water
in Drier Concentrate Multiple-Effect Evaporator
in Multiple-Effect Evaporator
*o


Fig. 5.-Flow and material balance sheet for the processing of citrus residues
into dried pulp and molasses.
The meal has passed through a screen of approximately 14 mesh3,
although this varies from plant to plant. An over-all view of
an experimental feed mill for producing dried citrus pulp is
shown in Fig. 6.
3 All mesh sizes refer to U. S. Bureau of Standards sieve numbers.


!


I


10


I


I


:






By-Products of Florida Citrus


Fig. 6.-Experimental feed mill at the Citrus Experiment Station, Lake Alfred.


Many processors make a sweetened pulp, adding 20 to 50
percent citrus molasses (made from the expressed press liquor)
to the curing peel residue. Sometimes more molasses is added,
depending on the marketing area, but care must be exercised,
since molasses addition darkens the color of the pulp. The


11


EliM i I IJ 4






Table 1.-Composition of Citrus Feed Products.

Nitrogen
Ref- Dry Crude Crude Free Crude
CITRUS PRODUCT erence Matter Protein Fibre Extract Fat Ash


Percent


Whole fruit
Grapefruit, cull
Oranges, grated
Tangerines

Undried peel residue
Citrus peel
Citrus peel, pressed
Grapefruit peel, pressed

Dried citrus residue
Citrus pulp
(71 analyses)
Citrus pulp
(10 anal. 64-65 prod.)
Citrus pulp, sweetened
Grapefruit pulp
(3 seasons)
Grapefruit pulp
(5 lots)


77
77
77


13
13
77



87


87


13.64
14.84
17.39


18.49
28.27
25.23



90.1

92.0
92.0


5 100

101 100


Percent Percent Percent Percent Percent
3.
1.07 1.39 10.03 0.64 0.51
0.96 1.58 11.34 0.32 0.64
1.01 1.38 13.62 0.80 0.58
a.

1.23 2.22 12.48 1.83 0.73
2.01 4.36 17.80 2.65 1.45
2.24 4.61 15.74 1.18 1.46


3.
5.9 11.5 62.7 3.1 6.9

6.2 12.0 64.0 4.9 4.9
5.3 9.3 66.6 2.8 8.0

6.4 12.1 56.9 5.5 -


7.0 15.3


5.9


6.5


Dried meal
Citrus meal 77


88.27 6.47 12.39 60.55 2.94 5.93


2.94 5.93


88.27 6.47 12.39


60.55







By-Products of Florida Citrus 13

actual quantity of molasses added to citrus pulp can be determin-
ed by Bissett's procedure (17). A comparison of the composi-
tion of dried citrus pulp, meal, sweetened pulp, and other citrus
products is shown in Table 1. The addition of molasses to citrus
pulp increases the carbohydrate content while decreasing the
fat, fibre, and protein content. Crude fat content of citrus pulps
is greater when the dried pulp is made from one of the more
seedy citrus varieties. Similarly, the fibre content is lower when
processing certain varieties of citrus. Dried citrus pulp is slight-
ly hygroscopic, and if proper care is not taken, the product will
increase in moisture content during storage. High moisture
in citrus pulp can cause mold formation, lowering of feed quality,
and generation of sufficient heat to cause spontaneous com-
bustion.
Dried citrus meal has slightly higher fibre, nitrogen-free ex-
tract, and ash contents than citrus pulp, but is lower in fat con-
tent, according to Kirk and Davis (78). The meal was found
by Becker and Arnold (14) to weigh 0.97 pound per quart, while
citrus pulp weighed from 0.57 to 0.80 pound per quart. Com-
mercial practice has established 25 pounds per cubic foot as a
reasonable average density for dried citrus pulp. When placed
in storage, 120 cubic feet per ton of dried pulp is allowed for
stacked bags and aisles.
Costs of processing, warehousing, and selling dried citrus
pulp and molasses have been analyzed by Spurlock and Hamil-
ton (115).

Processing Variables
Pressing Operation.-Plants that operate continuously find
it desirable to press the peel and produce both dried citrus pulp
and molasses. Considerable savings can be effected by the use
of multi-stage evaporators, even though greater capital expendi-
tures are necessary. The water is more efficiently evaporated
in such equipment. Citrus molasses, however, is not as economi-
cal an outlet as citrus pulp. Plants that operate intermittently
often find it more economical to dry the unpressed peel, since
overhead and labor costs are considerably lower. An alternative
to pressing is used in Texas (112). The limed peel is placed
temporarily in 10-ton curing bins that allow the bound liquor
to drain away as it is released. Drying cured citrus peel residue
without pressing is complicated by the greater tendency of the







Florida Agricultural Experiment Stations


residue to stick and burn in the drier. This problem is alleviated
by recycling a portion of dried or semi-dried peel. Sometimes
such recycling is necessary only when the drier is initially start-
ed. It has not always been practical to dry peel residue without
pressing, but only since residues of lower moisture content have
become more prevalent. Citrus peel residues with lower mois-
ture content became more available in Florida when propor-
tionately greater quantities of oranges were processed, as more
efficient juice extractors became available, and as clean-up water
was more carefully segregated.
There are three continuous presses found in the Florida cit-
rus industry. They are the Davenport press, the Louisville con-
tinuous press, and the Zenith pulp press.
In a Davenport press, the cured citrus residue is conveyed to
the top opening of an intake hopper and dropped between two
large revolving perforated disks. The disk faces are progres-
sively closer as they approach the discharge port. The increas-
ing pressure expels the press liquor through the minute openings
of the perforated disks. The press liquor drains, from the bot-
tom of the press. The fibrous character of the peel acts as a
filtering medium, aiding the screen plates in preventing the
fine solids from passing off with the liquid. The compressed
peel is removed continuously by a discharge bar that forces it
out the exit after a three-fourths revolution.
The Louisville continuous press is composed of a sectional,
endless belt of perforated hinged plates which pass continuously
over a series of supporting rolls. Each perforated metal section
offers a pressing surface. The section passes between a series
of paired rollers, one a supporting roller, the other a pressure
roller. As the cured pulp is fed to the press, it forms a fibrous
mat that retains the fine solids. The series of paired rollers
provide an almost continuous wringing action, forcing the press
liquor through the perforated filtering plates and discharging
the compressed pulp at the far end.
The Zenith continuous pulp press is essentially a vertical
screw press. It consists of a heavy, tapered, screw-type spindle
surrounded by a series of downward deflectors. This spindle is
perforated on the lower half and revolves at a relatively low
speed inside a reinforced cylindrical screen of stainless steel.
The cured peel enters the press at the top and during its down-
ward movement is constantly rolled over and continuously forced
by screw deflectors through a restricted, tapered opening. Vanes


14







By-Products of Florida Citrus


projecting through the outer screen act to retard and turn over
the pulp while it is compressed. Press liquor is forced through
the small perforations of the outer cylindrical screen, as well
as through those of the tapered spindle. At the bottom, the
pulp is still under pressure and is forced through a second re-
stricted, tapered opening to remove more press liquor. Fig. 7
illustrates this last type of press.
Drying Operation.-Three types of driers are found in this
industry: The direct-fired rotary, steam-tube rotary, and a
triple pass parallel heat flow rotary. These three types of driers
are shown schematically in Fig. 8.
The direct-fired rotary is composed of a long cylindrical shell,
usually 8 feet in diameter and 60 feet long. It is fired by oil,
and the hot combustion gases pass directly over the wet pulp
and in the same direction.
The steam-tube rotary drier has a shell similar to the
direct-fired rotary, but the wet pulp and air are heated by
steam tubes within the shell of the drier. The hot air flows
countercurrent to the pulp. Baffles, attached to the rotating
shell, move the pulp slowly through the drier. These driers are
adapted to multiple-stage drying.
The third type drier, a triple pass parallel heat flow rotary,
uses hot combustion gases from a direct-fired furnace for drying.
Internal baffles keep the pulp turning over and moving slowly
through the drier. The hot water-laden gases flow in the same
direction as the pulp and discharge into a cyclone separator for
elimination.
Among the many disadvantages attributed by Heid (43) to
oil-fired rotary driers are excessive kiln temperatures, burning
of fines, lower yield, and the fire hazard from bagging burning
particles. These are eliminated by multiple-stage drying. Three
kilns maintained at 230' F can be used to dry the pulp to 32
percent moisture, and drying can be completed in a fourth kiln
at a gas discharge temperature of 180 F. A steam-tube rotary
drier is ideally used as the fourth drier, since it allows closer
temperature control. This arrangement is generally more ex-
pensive because a boiler is needed, but exhaust low pressure
steam from a cannery may be used advantageously if available.
When a comparison was made by Pulley and von Loesecke
(101) of dried grapefruit pulp manufactured by three types of
driers, they found no significant difference between the products


15







16 Florida Agricultural Experiment Stations
























0 '
*.


Fig. 7.-Zenith pulp press. (Photograph courtesy Jackson &r Church Company,
Saginaw, Michigan.)








By-Products of Florida Citrus


Pulp


TRIPLE PASS DIRECT FIRED DRYER


STEAM TUBE ROTARY DRYER


Ip


ROTARY DIRECT FIRED DRYER


Fig. 8.-A schematic diagram of three types of driers for citrus pulp.


17







Florida Agricultural Experiment Stations


except where pressing had been avoided. None of the samples
contained carotene after drying. Carotenoids can be retained in
citrus pulps, however, by avoiding the lime addition and drying
very carefully. When Hamlin orange and Dancy tangerine peels
were dried carefully in the laboratory and evaluated as poultry
pigment sources, 180 and 350 milligrams of carotenoids per kilo-
gram were found4 respectively. Even higher carotenoid content
can be expected with the shorter drying cycle of a commercial
drier.
Moisture content of peel residue is an important variable
that can profoundly influence the drying process. It need not,
however, have any effect upon the quality of the manufactured
dried pulp. Grapefruit peel, for example, will have a higher
moisture content than orange peel. Similarly, truck-transported
peel usually will have a higher moisture content than directly
extracted residue. Recovery of oil from the peel will also in-
crease the moisture content of the peel residue. In the FMC-In-
Line extractor, mist spray cups increase oil yields form 50 to
100 percent, but add approximately 6 pounds of water per 90
pounds of oranges. Residue from a citrus sections production
line has considerably greater juice content than citrus residue
from any other source. Consequently, it can be expected to be
very wet. Moisture content correlates directly with the con-
version ratio of wet peel residue to dried citrus pulp. At one
time, a 10 to 1 conversion ratio was considered a typical in-
dustry average, while today it is probably about 5.5 to 1. Under
the best conditions, however, it could be as low as 3.8 to 1.
Peel residue of high moisture content not only decreases pro-
duction capacity, but also encourages sticking in the drier. The
latter condition causes burning in the drier and a greater pro-
portion of charred particles in the dried citrus pulp. If high
moisture content is a persistent condition, it is almost im-
perative that continuous presses be used.
Peel residues also will vary in physical appearance when
different juice extractors are used. The residue from an FMC-
In-Line extractor is shown in Fig. 9 and that from a Brown
extractor in Fig. 10. There are advantages inherent with each
type of residue. Peel from an FMC extractor has more cells
broken, which aids in drying, but it probably will yield more
fines. Peel from a Brown extractor has the advantage of being
'Personal communications with Distillation Products Industries.


18







By-Products of Florida Citrus


Fig. 9.-Appearance of peel processed in an FMC-ln-Line Juice extractor with
oil recovery accessories. (Photograph courtesy Food Machinery Corpora-
tion, Lakeland.)


Fig. 10.-Peel residue leaving a Brown Citrus Machinery Corporation reamer.


19







Florida Agricultural Experiment Stations


suited for further processing into food products such as candied
peel, marmalade, and dehydrated peel. Each of these extractors
can be adapted to segregate the residue into an inner fruit por-
tion and an outer peel portion. An arrangement of this type
presumably could simplify the recovery of more by-products.


Utilization
Dried citrus pulp finds its main use as a feed for dairy and
beef cattle. It is considered to be a desirable bulk carbohydrate
concentrate that is fairly high in energy and a good source of
calcium, but low in phosphorus and carotene (14). Other char-
acteristics found by Becker and Arnold (14) for citrus pulp
were that it exerts a mildly laxative action upon the digestive
tract, gives the hair coat a sleek glossy appearance, and often
is the most economical local source of total digestible nutrients.
Supplemental additions are needed, however, for it to become a
balanced dairy ration. Citrus pulp has been favorably used as
the main energy feed in the maintenance and fattening rations
for beef cattle by Kirk and Davis (78). When citrus pulp was
compared with corn feed meal and ground snapped corn in drylot
trials using young growing steers, Peacock and Kirk (98) found
no significant differences in gain, grade improvement, or dress-
ing percentage. The rations were balanced with adequate pro-
tein and other essential nutrients.
Nowadays, dried citrus meal is more usually available as
extruded pellets, made by adding citrus molasses or by steaming
the meal. These pellets are blended again with dried citrus pulp,
or used directly as an ensilage ingredient. Feed value is essen-
tially the same as for pulp. The fines or dust are less valuable
than pulp and are sold as a fertilizer conditioner or burnt as a
heating fuel by the processor.


CITRUS MOLASSES
Citrus molasses, as now manufactured in Florida, is required
to meet minimum state standards. It must contain 45 percent
total sugars, expressed as invert sugar, and have a Brix of not
less than 35.5 by double dilution. Citrus molasses weighs ap-
proximately 11.3 pounds per gallon and closely resembles the
more abundant blackstrap molasses.


20







Florida Agricultural Experiment Stations


suited for further processing into food products such as candied
peel, marmalade, and dehydrated peel. Each of these extractors
can be adapted to segregate the residue into an inner fruit por-
tion and an outer peel portion. An arrangement of this type
presumably could simplify the recovery of more by-products.


Utilization
Dried citrus pulp finds its main use as a feed for dairy and
beef cattle. It is considered to be a desirable bulk carbohydrate
concentrate that is fairly high in energy and a good source of
calcium, but low in phosphorus and carotene (14). Other char-
acteristics found by Becker and Arnold (14) for citrus pulp
were that it exerts a mildly laxative action upon the digestive
tract, gives the hair coat a sleek glossy appearance, and often
is the most economical local source of total digestible nutrients.
Supplemental additions are needed, however, for it to become a
balanced dairy ration. Citrus pulp has been favorably used as
the main energy feed in the maintenance and fattening rations
for beef cattle by Kirk and Davis (78). When citrus pulp was
compared with corn feed meal and ground snapped corn in drylot
trials using young growing steers, Peacock and Kirk (98) found
no significant differences in gain, grade improvement, or dress-
ing percentage. The rations were balanced with adequate pro-
tein and other essential nutrients.
Nowadays, dried citrus meal is more usually available as
extruded pellets, made by adding citrus molasses or by steaming
the meal. These pellets are blended again with dried citrus pulp,
or used directly as an ensilage ingredient. Feed value is essen-
tially the same as for pulp. The fines or dust are less valuable
than pulp and are sold as a fertilizer conditioner or burnt as a
heating fuel by the processor.


CITRUS MOLASSES
Citrus molasses, as now manufactured in Florida, is required
to meet minimum state standards. It must contain 45 percent
total sugars, expressed as invert sugar, and have a Brix of not
less than 35.5 by double dilution. Citrus molasses weighs ap-
proximately 11.3 pounds per gallon and closely resembles the
more abundant blackstrap molasses.


20







By-Products of Florida Citrus


Processing Procedure
Briefly, citrus molasses is manufactured by concentrating
the bound juice that is released from limed, cured, and pressed
citrus peel residue. The released juice is called press liquor and
contains 9 to 15 percent dissolved solids, more than half being
sugars. This liquor is straw-colored and turbid in appearance
and has a pH ranging from 5.0 to 7.0. The press liquor will
include, at times, quantities of a more dilute peel-oil recovery
effluent that would be difficult to dispose of by customary sanita-
tion procedures. The proportion of press liquor released from
cured citrus residue is quite variable and is dependent upon the
variety of fruit, the moisture content of the cured residue, and
the pressure exerted upon the residue by the continuous presses.
A typical example of a flow and material balance with grape-
fruit is shown in Fig. 5. The Brix of the press liquor expressed
from oranges is higher than that from grapefruit, while in each
species the Brix of the peel juice can be expected to be approxi-
mately 15 percent higher than the corresponding fruit juice.
Since orange peel has a critically lower moisture content than
grapefruit peel, it often is dried without pressing.
The conversion of citrus press liquor to molasses begins by
separating the unwanted larger pulp particles from the released
press liquor with a vibrating screen. The liquor passing through
a 40 to 80 mesh vibrating screen is passed to a temporary stor-
age tank until it can be pasteurized. Heat exchangers flash the
liquid under pressure from 240 F to atmospheric conditions.
This operation serves four purposes: peel oil is distilled off and
recovered as an additional by-product, the high temperature kills
all spoilage organisms, calcium citrate and other calcium salts
are precipitated, and the flocculation and sedimentation of other
suspended matter are aided. At this point, some processors par-
tially clarify the liquor prior to its entering the evaporators.
Suspended matter is allowed to settle from the hot press liquor
in special storage tanks. Multiple-effect evaporators concentrate
the clarified hot press liquor to 50' Brix, whereupon it is usu-
ally screened (40 mesh) to eliminate the larger scale particles
that may have loosened in the evaporator. A forced circulation
finishing pan completes the concentration to 72 Brix.
In a few instances, a spray evaporator has been used to con-
centrate citrus press liquor with hot flue gases. Evaporation
is continued in a second chamber that uses the latent heat of


21







Florida Agricultural Experiment Stations


vaporization from the first stage. The final concentration is
obtained with the usual finishing pan. In this arrangement,
stripper oil is not recovered, and molasses stability is said to
have suffered and gelling to have occurred occasionally. The
latter problems are presumably due to the low processing tem-
peratures that neither inactivate the enzymes nor pasteurize
the product sufficiently.
A typical analysis of citrus molasses is shown in Table 2,
compiled from published (45, 62, 68) and unpublished data of
the authors. Standards for citrus molasses have been established
at a lower level of concentration than other types of molasses to
avoid a viscosity problem. This condition is brought about by
the increased quantity of insoluble suspended material formed
during the conversion of press liquor to citrus molasses. Com-
pared to blackstrap, citrus molasses has the advantage of hav-
ing a higher protein content and lower ash analysis.
Annual production of citrus molasses at five-year intervals
is compared in Fig. 2, which shows production to have remained
relatively constant since 1946. A variable portion of the molasses
manufactured is blended with citrus pulp, which is often a more


Table 2.-Typical Analysis of Florida Citrus Molasses.


Brix ---------
Sucrose % ----
Reducing sugars % ----
Total sugars % --
Moisture % --
Protein (N X 6.25) %
Nitrogen-free extract %
Fat % ..--------
Fibre % -----


Ash %
Glucosides % _
Pentosans %
Pectin %
Volatile acids %
pH .....-_-----


72.0 Potassium (K) %
20.5 Calcium (Ca) %
23.5 Sodium (Na) %


45.0
29.0
4.1
62.0
0.2
0.0


Magnesium (Mg) %
Iron (Fe) % --
Phosphorus (P) %
Manganese (Mn) %
Copper (Cu) % -
Silica (SiOz) % ---


1.1
0.8
0.3
0.1
0.04
0.06
0.002
0.003
0.04


4.7 Sulphur (S) % -- 0.17
3.0 Boron (B) % -------_. --.--- 0.0006
1.6 Niacin (ppm) --- 35
1.0 Riboflavin (ppm) ---.........- 11
0.04 Pantothenic acid (ppm) -- 10
5.0 Viscosity 250 C. (centipoises) 2000


22







By-Products of Florida Citrus


profitable outlet. The manufacturing costs for citrus molasses
have been reported recently by Spurlock and Hamilton (115).

Processing Considerations
Studies (55, 56) of the viscosity problems of citrus molasses
have shown that clarification of citrus press liquor is the most
beneficial processing change. This is best accomplished by flash
pasteurization, which hastens the settling of the insolubles in
press liquor by eliminating peel oil buoying action. When press
liquor is clarified and concentrated to molasses, a much darker
product is obtained. The darker color of this improved product
is sufficient to prejudice some into believing the product has
been burnt or overcooked, whereas it appears dark only because
of fewer suspended particles to reflect the incident light.
In storage, citrus molasses undergoes changes that lead to
further viscosity problems. A gelatinous structure is formed
slowly in molasses during storage, and recycling or stirring is
effective toward inhibiting this type of viscosity increase. Occa-
sionally, there is a gradual crystallization of naringin during
prolonged storage, which also can greatly increase citrus mo-
lasses viscosity.
In storage, citrus molasses decreases in pH as during the
concentrating period. Processing press liquor to molasses reduces
the pH by approximately one unit, while storage throughout one
season would decrease the pH by another 0.4 unit. The latter
decrease is variable and is dependent on storage time and ori-
ginal pH. The lower pH increases the corrosive action of citrus
molasses on the storage tanks and other iron equipment.
Another problem in the manufacture of citrus molasses is
the large quantity of scale formed on the heat transfer surfaces
in the concentrating equipment. Analyses have shown this scale
to be predominantly calcium citrate. The condition is encouraged
by the lime addition needed for curing the citrus residues. The
industry has met the problem with different approaches. Most
processors have found it advantageous to encourage scaling in
the press liquor preheaters, which are more readily cleaned
than an evaporator. Others go further and use parallel arrange-
ment of preheaters that permit alternate cleaning without a
shutdown. Kilburn (75)was able to substitute waste lye from
the sectionizing plant for part of the lime addition. This de-
creased scaling and eliminated a portion of the load on the waste


23







24 Florida Agricultural Experiment Stations

disposal system. Substitution of magnesium for a portion of the
calcium, such as by using a calcined dolomitic limestone in place
of high purity dehydrated lime for curing peel residue, offers
another possible alternative toward decreasing scale. The pre-
heaters and citrus molasses evaporators are cleaned of scale
with a boiling solution of caustic or a mixture of caustic and
soda ash that is circulated over the heat exchange surfaces.
Spontaneous foaming has been a problem of all types of
molasses, and although it happens only infrequently with citrus
molasses, it can represent a major economic loss. The exact
cause of foaming is unknown; however, a reduction of viscosity
and suspended solids greatly reduces the likelihood of it happen-
ing. Its occurrence is decreased also by avoiding the mixing
of old and new molasses, by avoiding alkaline processing condi-
tions, and by storing only cooled molasses. Avoidance of condi-
tions encouraging microbial activity also is suggested. Once
foaming has started, it usually can be brought under control
by one of the following: 1, reprocessing; 2, recirculating with
delivery pump; 3, stirring with compressed air; and 4, occasion-
ally by injecting sulfur dioxide. An antifoam agent is needed
in every case.


Utilization
Citrus molasses finds its greatest market presently as a feed.
As such, it was estimated by Becker et al. (15) to contain 1.4
percent of digestible crude protein and 56.7 percent of total
digestible nutrients. The bitterness imparted by naringin to
citrus molasses was not a detriment in feeding dairy cows.
Grasses were effectively ensiled with 2 and 4 percent citrus
molasses. Citrus molasses was used by Baker (12) to replace
one-half of the ground snapped corn in a steer fattening ration
without reducing gains, grade, or yield. In a similar application,
Kirk and Davis (78) found citrus molasses to be palatable for
all classes of beef cattle and to be one of the cheapest energy
feeds available in central Florida. The comparative feeding
value of citrus molasses and blackstrap molasses was shown to
be about equal, with citrus molasses being more palatable in
steer feeding trials by Chapman (22) and Kirk (76). This be-
came a slight disadvantage when steers ate too greedily at the
expense of efficient utilization.







By-Products of Florida Citrus


When citrus molasses was fed to swine, Cunha and co-
workers (25) found that molasses could be used to replace corn
in the feeding ration at the 10, 20, and 40 percent level depend-
ing on the age of the pigs. It took three to seven days for the
animals to become accustomed to the taste of citrus molasses.
Over-all usage shows that tons of citrus molasses are con-
sumed by cattle each year in Florida. It is also a source for
recovery of citrus bioflavonoids and for the production of a
beverage-type ethyl alcohol by fermentation. Citrus molasses
has been shown also to have potential use in the production of '
yeast, lactic acid, bland syrup, citrus vinegar, 2,3-butylene
glycol, riboflavin, citric acid, methane, and other products.


CITRUS PEEL OILS
The peel oil, or essential oil as it is sometimes called, is the
first product recovered from citrus cannery residue. Each of the
Citrus species orange, grapefruit, tangerine, lemon, and lime
-has an oil that commands a price which justifies the operation
of a plant for its recovery.
Citrus oils are confined in oblate, spherical-shaped oil glands
that are located irregularly in the outer mesocarp or flavedo of
the fruit. These glands or intercellular cavities have no walls
of the usual type and are imbedded at different depths in the
flavedo of all citrus fruits. The cells surrounding the oil glands
contain an aqueous solution of sugars, salts, and colloids, and
exert some pressure on the glands. Winton and Winton (132)
and Braverman (18) more thoroughly describe the exact loca-
tion of these oil sacs in the structure of the flavedo of the orange.
Methods of oil extraction used in Florida were investigated
by Kesterson and Hendrickson (67, 69, 70), and results of
studies relative to the physical and chemical properties of Flo-
rida citrus oils are presented.


Methods of Commercial Manufacture
General Processing Procedure.-Citrus peel oils have been
expressed in Florida by six different types of equipment: 1,
Pipkin roll; 2, screw press; 3, Fraser-Brace extractor; 4, FMC
rotary juice extrator; 5, FMC-In-Line extractor; and 6, AMC
scarifier. To secure the oil from the peel of citrus fruits, oil sacs


25







By-Products of Florida Citrus


When citrus molasses was fed to swine, Cunha and co-
workers (25) found that molasses could be used to replace corn
in the feeding ration at the 10, 20, and 40 percent level depend-
ing on the age of the pigs. It took three to seven days for the
animals to become accustomed to the taste of citrus molasses.
Over-all usage shows that tons of citrus molasses are con-
sumed by cattle each year in Florida. It is also a source for
recovery of citrus bioflavonoids and for the production of a
beverage-type ethyl alcohol by fermentation. Citrus molasses
has been shown also to have potential use in the production of '
yeast, lactic acid, bland syrup, citrus vinegar, 2,3-butylene
glycol, riboflavin, citric acid, methane, and other products.


CITRUS PEEL OILS
The peel oil, or essential oil as it is sometimes called, is the
first product recovered from citrus cannery residue. Each of the
Citrus species orange, grapefruit, tangerine, lemon, and lime
-has an oil that commands a price which justifies the operation
of a plant for its recovery.
Citrus oils are confined in oblate, spherical-shaped oil glands
that are located irregularly in the outer mesocarp or flavedo of
the fruit. These glands or intercellular cavities have no walls
of the usual type and are imbedded at different depths in the
flavedo of all citrus fruits. The cells surrounding the oil glands
contain an aqueous solution of sugars, salts, and colloids, and
exert some pressure on the glands. Winton and Winton (132)
and Braverman (18) more thoroughly describe the exact loca-
tion of these oil sacs in the structure of the flavedo of the orange.
Methods of oil extraction used in Florida were investigated
by Kesterson and Hendrickson (67, 69, 70), and results of
studies relative to the physical and chemical properties of Flo-
rida citrus oils are presented.


Methods of Commercial Manufacture
General Processing Procedure.-Citrus peel oils have been
expressed in Florida by six different types of equipment: 1,
Pipkin roll; 2, screw press; 3, Fraser-Brace extractor; 4, FMC
rotary juice extrator; 5, FMC-In-Line extractor; and 6, AMC
scarifier. To secure the oil from the peel of citrus fruits, oil sacs


25







Florida Agricultural Experiment Stations


must be burst by pressure or punctured by rasping and the oil
washed away. Water is always required, usually as a spray.
The general processing procedure, used after extraction of oil
from peel, is very similar in most commercial plants. All of the
above-mentioned methods of extraction give an emulsion of oil
and water. The oil is separated centrifugally from the aqueous
phase by passing the emulsion through a sludger (8,000 to
10,000 rpm) and then through a polisher (15,000 to 18,000 rpm).
Care is taken to remove the last traces of water in the polisher,
since its presence could bring about detrimental changes.
Following separation, the oil is stored for approximately one
to four weeks at 32" to 40' F. During this winterizing or low-
temperature treatment, waxy materials are encouraged to sepa-
rate and settle from the oil. These waxy materials are aurap-
tenes and steroids in grapefruit and orange oil, tangeretin in
tangerine oil, and limettin and isopimpinellin in lime oil. The
clear oil is decanted into stainless steel, plastic lined, or tin-
dipped containers and is then stored at 40 to 70' F. Air is
preferably excluded from the container to prevent oxidative
deterioration. This is accomplished either by filling the con-
tainers to capacity or by displacing the air with carbon dioxide
or nitrogen.

Pipkin Roll Method of Extraction.-In this method, the oil
is expressed by passing peel of the fruit between two striated
rollers of stainless steel that turn in opposite directions. The
distance between the two rollers is adjusted so that the pressure
against the peel is just sufficient to puncture the oil cells without
breaking or rasping the peel. Small striations or grooves are
distributed over the entire surface of the rolls. They are of a
depth sufficient to receive the oil from the oil cells and keep it
out of contact with the peel, thus reducing its absorption by the
albedo of the fruit.

Screw Press Method of Extraction.-In this method, tapered
screws press the peel against a perforated screen, thereby
squeezing out the oil. The operation can be carried out with the
screws in either a vertical or horizontal position. Water may
or may not be used in the pressing operation. The yield of oil
is directly proportional to the surface area of the peel coming
into contact with the screen. Consequently, five 2-ton presses
will give a greater yield of oil than one 10-ton press.


26







By-Products of Florida Citrus


Fraser-Brace Extractor.-Whole fruits are passed through
a corridor of carborundum rolls in this process. As the fruit
passes through the extractor, it is repeatedly turned over, and
abrasive rolls rasp the flavedo from the fruit. Water sprays
directed onto the fruit and rolls wash away the oil and grated
peel. The oil-water emulsion and peel raspings are passed over
a screen to remove the suspended solid particles. The emulsion
passing through the screen is transferred to settling tanks,
where it is held from 3 to 12 hours to effect complete settling and
to allow a more concentrated emulsion to rise. The machine is
completely enclosed, and very little loss of oil is encountered.

FMC Rotary Juice Extractor.-The Food Machinery Cor-
poration rotary juice extractor provides a method whereby both
the juice and the peel oil emulsion from whole fruit are obtained
simultaneously, but in such a manner that they do not come in
contact with each other to any great extent. This machine is of
the rotary type and has 24 squeezing heads which are all actuated
by a common cam. Whole fruit is fed into a squeezing cup where
just enough pressure is applied to remove all juice from the
fruit and at the same time rupture the oil cells. The juice and
the oil emulsion are collected in separate trough assemblies. This
machine has been replaced by a more efficient counterpart called
the FMC-In-Line Extractor.

FMC-In-Line Extractor.-The FMC-In-Line Extractor (18)
was so named because the series of extraction cups are situated
in a straight line. This unit is used for oranges, tangerines,
lemons, limes, and grapefruit. The upper cups are mounted on
a common crossbar which, by means of a cam-drive, is moved
in a fixed up and down path. The corresponding lower cups are
held in rigid position. The sides of these cups consist of numer-
ous fingers that intermesh when the upper and lower cups are
brought together. A circular cutter tube is fastened in the bottom
of each of the lower cup members, and this protrudes below into
a strainer tube. Mounted below the lower cups and enclosing the
strainer tubes is a manifold which is common to all of the lower
cups and strainer tubes of a single machine. An unperforated
orifice tube closely fitted inside the strainer tube slides up and
down inside the cutter.
The fruit are delivered by a conveyor belt to the rear side
of the machine, where there is a joined series of runways, one


27







Florida Agricultural Experiment Stations


for each cup. A cam-driven lift functions as a positive means
of placing fruit individually into the lower cups. The motion
of lift is synchronized with the movement of the upper cups and
also with the orifice tubes mounted on the lower bar.
When the fruit is placed in the lower cup, the upper cup is
moved down in a smooth stroke, pressing the fruit against the
cutter tube. This cuts a plug in the fruit. As the upper cup con-
tinues its downward stroke, the entire inner portion of the fruit
is forced down into the strainer tube within the manifold. At
the same time, the orifice tube moves upward inside of the
strainer tube, thus causing the juice to be forced through the
perforated strainer tube into the manifold. The stroke is com-
pleted when the upper cup completely meets the cutter tube, thus
sealing off this tube and cutting a plug in the upper portion of
the fruit. At this point of the stroke, the inner portion of the
orange which has been forced into the strainer tube is com-
pletely pressed of juice. At the same time, the peel of the fruit
is shredded and dropped into a screw conveyor trough which
carries it to the by-product operation.
When an oil cup assembly is used to recover the peel oil
expressed during the juice extraction operation, the upper and
lower cups are reversed. Cup-shaped baffles surround the fingers
of the upper cup, and as the oil is released by the shredding
action, it is collected on the baffles and directed to one side of
the extractor. Considerable volatilization of the oil accompanies
this operation, as evidenced by the aroma of the surrounding
atmosphere. The oil and aqueous matter expressed from the
outer peel, along with small particles of outer peel, are mixed
with a small amount of water to provide fluidity. This mixture
is run through a finisher equipped with a fine screen to give an
oil emulsion from which peel oil is separated later.
An improvement for increasing the yield of oil may or may
not be added to the above machine. At the same instant the oil
is released from the peel, a fine mist of water is sprayed which
prevents loss of oil due to atomization. It has been reported that
yields have increased 50 percent by the addition of these cups.

AMC Scarifier.-The American Machinery Corporation meth-
od of releasing oil from the peel of citrus fruits is essentially a
refinement of the "Avena," "Speciale," and other rasping
methods used in Italy and other Mediterranean countries. This


28







By-Products of Florida Citrus


scarifier is designed for continuous operation, and it is placed
in the conveyor line to the juice extractors.
The scarifier resembles the universally used transverse brush
washer in its design and manner of handling the fruit. It con-
sists of a frame in which cylinders made of stainless steel sheets
that have been pierced with a square punch are mounted at
right angles to the flow of the fruit. The punch has pierced
the stainless steel in such manner as to cause sharp points of
the metal to stand up similar to the points in a nutmeg grater.
It is these points that puncture the oil cells of the citrus peel.
These cylinders, usually about 22 in number, rotate on a
stainless steel shaft. A variable speed drive controls the speed
of rotation to permit adjustment to fruit of varying size and
characteristics. The stainless steel cylinders are actually formed
of four pieces of metal fastened to a shaft by means of casting
to which they have been screwed. Each piece forms approxi-
mately one-fourth of the cylinder. They are so arranged that
they are self-cleaning of the raspings.
The frame in which these rolls are mounted is inclined up-
ward at a rather steep angle. This permits the fruit to pile up
deeply at the intake end and assures additional piercing action
by the weight on the bottom fruit that is in contact with the
stabbed metal.
The entire interior of the enclosure contains a mist of water
provided by fog-type spray nozzles. This water serves to wash
the released oil from the surface of the fruit, to saturate the
flavedo with moisture and thus restrict the reabsorption of the
oil by the fruit, and to maintain a moisture saturated atmos-
phere in the area above the fruit that discourages escape of the
oil through openings in the enclosure. At the discharge end of
the machine, the spray nozzles provide heavier streams of water
to wash the fruit and brushes.
The oil laden water from the scarifier is captured as an
emulsion in a stainless steel pan beneath the machine.

Coldpressed Citrus Oils
Relation of Yield to Properties and U.S.P. Specifications.-
The U.S.P. specifications (121) for orange oil require a specific
gravity between 0.842 and 0.846 (250 C/25" C), a refractive
index between 1.4723 and 1.4737 (20' C), an evaporation residue
greater than 1.7 percent, and an optical rotation of +94 to


29







Florida Agricultural Experiment Stations


+99 (25 C). The 10 percent distillate of the oil should have
a refractive index 0.0008 to 0.0015 units less than the original
oil and an optical rotation equal to or not more than +2 greater
than original oil.
The factor found to influence the physical and chemical pro-
perties of coldpressed oil of orange to the greatest extent was
the yield of oil secured from the peel. Higher oil yields lead
to increased values of the specific gravity, evaporation residue,
and refractive index, but decrease the values for optical rotation.
As the yield of oil is increased, more high-boiling, high molecu-
lar-weight constituents are evidently extracted. The presence
of a higher percentage of these compounds in the oil causes a
reduction in the percentage of d-limonene. This leads to lower
optical rotation values, since d-limonene is the most optically
active component in the oil.
Yields of oil obtained by the various methods of processing
fluctuate from 1.85 pounds per ton of peel to 9.70 pounds per
ton of peel. Commercial plants often have more peel than it is
possible for them to process for maximum amount of oil recover-
able from the peel. This being the case, the plants are operated
so as to produce the maximum amount of oil on an hourly basis.
To do this, they partially extract the oil from a large quantity
of peel rather than secure the maximum recovery of oil from a
smaller quantity of peel. Hence, they may secure very low yields
of oil despite their capability of obtaining much higher yields
with the same equipment.
Any processor can produce an oil meeting U.S.P. specifica-
tions using available equipment, provided he is willing to operate
it in such manner that he will secure the necessary yield of oil.
On the basis of the data accumulated, it is estimated that a yield
of 6.5 to 8.5 pounds of oil per ton of peel from mid-season
oranges or the extraction of 45 to 60 percent of the total amount
of oil in the peel of any orange variety of good maturity will
result in a cold pressed oil that will meet the specifications of
the United States Pharmacopoeia (121).

Effects of Aqueous Phase on Aldehyde Content.-Although
the flavor and aroma of an oil of orange is dependent upon all
of its many constituents, the aldehyde content is recognized as
having special importance even though it is not included in the
U.S.P. specifications.


30







By-Products of Florida, Citrus


In one plant where other variable factors were kept con-
stant while the water used in the process was reduced from ex-
tremely large quantities to an equivalent of 100 gallons of
aqueous phase per gallon of oil produced, the aldehyde content
increased from 1.08 to 1.64 percent, a 52 percent increase.
Accordingly, it was evident that to produce an orange oil of
high aldehyde content, the amount of aqueous phase in contact
with the oil during processing should be reduced as much as is
practical under operating conditions.
Recent work has shown that as the quantity of aqueous phase
is increased, the amount of insoluble solids increases. These
insoluble solids, primarily pulp particles, presumably act as
ion-exchange resins and selectively absorb constituents from
the oil. Loss of aldehydes in an oil recovery plant using large
quantities of water, therefore, may be as readily explained as
by absorption loss as by solubility loss.

Relation of Fruit Variety to Properties.-The physical prop-
erties of expressed orange oils obtained from different varieties
of fruit were not significantly different. There were processing
differences, of course, but even these remained constant through-
out the season.
The aldehyde content of coldpressed oils of orange was high-
est when made from 'Valencia' oranges. Mixtures of 'Pineapple'
and seedling oranges yielded an oil with a lower aldehyde con-
tent, while mixtures of 'Hamlin' and 'Parson Brown' varieties
gave an oil of the lowest aldehyde content.
Variety of fruit apparently had very little influence on the
ester content of the orange oils. Oil of orange produced by the
Fraser-Brace extractor was higher in esters than oils manu-
factured by any of the other methods. Oils from mid-season
varieties that were partially green in color were considerably
higher in ester content than those made by the same process
later when the fruit were completely orange in color. High
evaporation residue values were another characteristic of the
oils produced by the Fraser-Brace extractor.

Storage of Fruit Prior to Oil Extraction.-The length of time
fruit were stored prior to the extraction of the oil was another
factor which influenced the characteristics and quality. The
physical properties of coldpressed oils, of orange extracted from
fruit on the same day they were harvested were not significantly


31







Florida Agricultural Experiment Stations


different from those oils extracted from fruit stored for three
to five days before being extracted. Significant differences were
found, however, in the chemical properties. The ester content of
the oil from stored fruit was 31.3 percent higher than that from
fruit which had not been stored. The evaporation residue of
the oil from the stored fruit was 9.6 percent higher, and the
aldehyde content was 4.6 percent lower.
Effect of Maturity on Properties.-Here again, differences
were noted in the chemical characteristics rather than in the
physical properties.
The aldehyde content of Valencia orange oils increased as
maturity increased, reached a maximum when extracted during
the early part of the Valencia season from fruit that just passed
the maturity standards, and then decreased after peak maturity
had been reached. The ester content of these oils was lowest
when extracted during the early part of the Valencia season
and gradually increased as the fruit became more mature. Va-
lencia oranges that had passed peak maturity produced an oil
with the highest ester content of any oils secured during the
year.
Effect of Yearly Variations on Properties.-A comparison of
the 1947-48 fruit season, which was considered to be a very wet
year, and the 1948-49 fruit season, which was considered to be
a very dry year, was expected to show differences in the physical
and chemical characteristics of the oil. Only two factors, how-
ever, were affected to any extent. These were refractive index
and aldehyde content. The values for refractive index averaged
0.0008 of a unit higher during the dry 1948-49 fruit season.
Average values for aldehyde content of oils produced during the
wet 1947-48 and dry 1948-49 seasons were 1.75 and 1.49 percent,
respectively. Apparently, weather had some physiological effect
on the fruit which caused the aldehyde content of the oil to be
16.1 percent lower in the dry season.
Physicochemical Procedure to Determine Origin and Method
of Extraction.-The physicochemical properties of coldpressed
orange oils have revealed differences in the ultraviolet spectra
and in the evaporation residues that reflect the geographical
source of an oil and the method by which it was extracted.
Kesterson et al. (74) have shown that these two values could be
used as a basis to identify and characterize coldpressed orange
oils as in Table 3. The CD value is an optical density difference


32







By-Products of Florida Citrus


reading that measures the size of a UV peak. It is determined
at 330 m/ for orange oil by diluting 0.25 g to 100 ml with 95
percent ethanol and reading in a 10 mm cell.

Table 3.-Evaporation Residue and CD Values for Orange Oils.

Type Oil CD Evaporation Residue

California 0.10 to 0.20 Not significant

Florida:
Screw Press 0.20 to 0.40 Below 2%
FMC-In-Line 0.20 to 0.40 Above 2%
Pipkin Roll 0.40 to 0.60 Not significant



Characteristics and Composition.-The physical and chemical
properties for coldpressed orange oil samples, which were
secured from six commercial plants, are presented in Table 4.
Each of the plants used a different method for expressing the
oil. Maximum and minimum values for the properties of cold-
pressed grapefruit, tangerine, lemon, and lime oils produced by
the FMC-In-Line extractor are shown in Table 5. Approxi-
mately 75 percent of all the oils in Florida are produced by
this method. The other methods of extraction would bring about
property differences for each of these oils similar to those shown
for the coldpressed orange oils in Table 4.
Coldpressed orange, grapefruit, tangerine, and lime oils are
produced to a considerable extent in Florida. These oils are
composed of mixtures of hydrocarbons, oxygenated compounds,
and non-volatile residues. The hydrocarbons are primarily ter-
penes, while the oxygenated compounds are made up of a variety
of compounds aldehydes, esters, acids, alcohols, ketones, and
phenols. Non-volatile residues consist of resins and waxes.
The greatest advance in determining chemical composition
of essential oils has occurred during the past five years and
involves the use of gas liquid chromatographic (GLC) methods.
The approximate qualitative and quantitative composition of
Florida citrus oils (8, 9, 68, 71, 73, 133, 134) has been determin-
ed by GLC methods, but needs further study and clarification


33







Florida Agricultural Experiment Stations


before these analyses can be used generally for establishing any
new standards.

Distilled Citrus Oils
Distilled oil of orange, grapefruit, tangerine, or lime is
secured as a by-product in the processing of citrus fruit juice.
Some of the citrus peel oil becomes mixed with the juice as it
is extracted by the various types of juice extractors used in
the canneries. An excessive amount of peel oil in the juice is
considered detrimental to the quality of canned juice; therefore,
in most canning plants the oil content of the juice is reduced
to a desirable level by passing the juice through a de-oiler. The
juice is usually flashed in the de-oiler, which is operated under
a vacuum of 11 inches (190 F) to 25.5 inches (130 F). A vapor
mixture of oil and water is removed and is condensed. The oil
is separated from the condensate by decanting or centrifuging.
Vacuum steam-distilled oils obtained in this manner will have
properties slightly different from atmospherically steam-distilled
oils and presumably better flavoring qualities.
The maximum and minimum values for Florida distilled
orange, grapefruit, and lime oils as given in Table 6 are con-
sidered typical for high quality distilled oils. It was noted that
the distilled orange oil had an aldehyde content about 24 percent
higher and an ester content approximately 10 percent lower
than the corresponding average value for coldpressed oil. Simi-
larly, vacuum steam-distilled oil obtained in the de-oiling of
grapefruit juice was found to run approximately 90 percent
higher in aldehydes and 60 percent lower in esters than the
expressed oils. It seemed apparent that additional aldehydes
were extracted and removed from the citrus juice itself by the
de-oilers during commercial canning operation.
The lime oil samples of Table 6 were obtained from peel
which was first expressed to obtain coldpressed oil and then
steam distilled to produce the distilled oil of lime. The aldehyde
content was quite variable. This can be accounted for by the
fact that during processing some batches were more acidic than
others. The loss of aldehydes was considered to be due to the
degradation of the aldehydes by steam in the presence of citric
acid. Guenther (41) has shown that the combination of heat
and acid on lime oil has a marked effect on the aldehyde content
of the oil.


34







By-Products of Florida Citrus


Because of the relatively high price of lime oil, some proces-
sors distill the effluent from the centrifuges to recover more
distilled oils.

Citrus Stripper Oil
Stripper oil is obtained as a by-product from the manufac-
ture of citrus molasses. The name applies to the peel oil that is
stripped or recovered by distillation from citrus press liquor.
Since peel oil steam distills readily, the greater portion of the
0.20 to 0.50 percent in citrus press liquor can be recovered as
a condensate from the flash pasteurization of press liquor. Ap-
proximately 60 to 80 percent of the oil present is distilled and
recovered by flashing press juice from 240" F to its normal
atmospheric boiling point. It is estimated that a potential pro-
duction of over 10 million pounds of stripper oil exists per year
in Florida if all of this oil were recovered. Not all processors
are equipped to recover stripper oil, and molasses production is
sometimes avoided, so yearly production is considerably less.
Since press liquor is made usually from a mixture of citrus
fruit, recovered stripper oil represents similarly a mixture of
steam-distilled citrus oils. It frequently possesses a fine citrus
oil character, marred only by a slight distilled or heated char-
acter, and contains very little of the waxy material ordinarily
present in expressed citrus oils. Table 7 presents the physical
and chemical properties of this oil.
Factors important toward preventing autoxidation of d-limo-
nene during storage have been described by Newhall (92). It
is suggested that 50 to 100 ppm of butylated hydroxytoluene be
added and air scrupulously excluded by purging with nitrogen
or carbon dioxide.

Utilization
Citrus oils such as coldpressed orange, grapefruit, tangerine,
lemon, and lime find an amazingly wide and varied application
in at least 32 major industries such as beverage, food, perfume,
cosmetic, soap, pharmaceutical, paint, confectionery, condiment,
ice cream, insecticide, rubber, and textile, and for the scenting
and flavoring of many different types of products.
The most important outlet is the flavor industry, which
regularly consumes substantial quantities of the natural oils,
terpeneless oils, and fivefold concentrates. The latter are often


35







By-Products of Florida Citrus


Because of the relatively high price of lime oil, some proces-
sors distill the effluent from the centrifuges to recover more
distilled oils.

Citrus Stripper Oil
Stripper oil is obtained as a by-product from the manufac-
ture of citrus molasses. The name applies to the peel oil that is
stripped or recovered by distillation from citrus press liquor.
Since peel oil steam distills readily, the greater portion of the
0.20 to 0.50 percent in citrus press liquor can be recovered as
a condensate from the flash pasteurization of press liquor. Ap-
proximately 60 to 80 percent of the oil present is distilled and
recovered by flashing press juice from 240" F to its normal
atmospheric boiling point. It is estimated that a potential pro-
duction of over 10 million pounds of stripper oil exists per year
in Florida if all of this oil were recovered. Not all processors
are equipped to recover stripper oil, and molasses production is
sometimes avoided, so yearly production is considerably less.
Since press liquor is made usually from a mixture of citrus
fruit, recovered stripper oil represents similarly a mixture of
steam-distilled citrus oils. It frequently possesses a fine citrus
oil character, marred only by a slight distilled or heated char-
acter, and contains very little of the waxy material ordinarily
present in expressed citrus oils. Table 7 presents the physical
and chemical properties of this oil.
Factors important toward preventing autoxidation of d-limo-
nene during storage have been described by Newhall (92). It
is suggested that 50 to 100 ppm of butylated hydroxytoluene be
added and air scrupulously excluded by purging with nitrogen
or carbon dioxide.

Utilization
Citrus oils such as coldpressed orange, grapefruit, tangerine,
lemon, and lime find an amazingly wide and varied application
in at least 32 major industries such as beverage, food, perfume,
cosmetic, soap, pharmaceutical, paint, confectionery, condiment,
ice cream, insecticide, rubber, and textile, and for the scenting
and flavoring of many different types of products.
The most important outlet is the flavor industry, which
regularly consumes substantial quantities of the natural oils,
terpeneless oils, and fivefold concentrates. The latter are often


35






Table 4.-Maximum and Minimum Values for the Properties of Coldpressed Orange Oil Produced by Various Methods.
Fraser-Brace FMC Rotary FMC-In-Line AMC
Method of Extraction Pipkin Roll Screw Press Extractor Juice Extractor Extractor Scarifier
No. of Samples 10 34 9 65 62 2
Max. Min. Max. Min. Max. Min. Max. Min. Max. Min. Max. Min.

Sp. gray. 25" C/25 C 0.8432 0.8420 0.8426 0.8416 0.8458 0.8441 0.8443 0.8420 0.8438 0.8424 0.8449 0.8433

Ref. ind. Ng 1.4734 1.4718 1.4733 1.4719 1.4743 1.4730 1.4737 1.4722 1.4731 1.4725 1.4731 1.4728

Ref. ind. 10% dist. N0 1.4722 1.4708 1.4723 1.4707 1.4724 1.4703 1.4727 1.4707 1.4717 1.4715 1.4716 1.4716

Difference 0.0013 0.0007 0.0015 0.0007 0.0031 0.0016 0.0015 0.0010 0.0014 0.0010 0.0015 0.0012

Opt. rot a-' +98.05 +96.64 +97.80 +96.53 +96.30 +94.54 +97.57 +94.98 +97.08 +95.32 +96.70 +96.36

Opt. rot. 10% dist. a2, +98.31 +97.30 +98.65 +97.24 +98.70 +96.96 +98.73 +96.49 +97.92 +95.74 +98.16 +97.47

Difference 1.28 0.01 1.41 0.03 3.70 1.51 2.00 0.00 1.51 0.11 1.80 0.77

Aldehyde content % 2.02 1.63 1.55 0.92 1.65 0.93 2.04 1.17 1.96 1.54 1.86 1.86

Ester content % 1.01 0.15 1.09 0.04 1.63 0.35 1.34 0.08 -

Evaporation residue-% 2.42 1.07 2.03 1.37 4.93 3.12 3.22 1.85 3.08 2.45 4.00 2.80

CD 0.530 0.420 0.373 0.207 0.412 0.364 0.375 0.206 0.426 0.359
UV spectrum
0.25g Peak 0.850 0.670 0.570 0.360 0.713 0.623 0.673 0.388 0.726 0.673
M log E 100cc
Mi 330.5 329.5 330.1 329.2 329.0 328.0 330.0 329.0 330.0 330.0






Table 5.-Maximum and Minimum Values for the Properties of Coldpressed Grapefruit, Tangerine, Lemon, and Lime Oils Extracted
by the FMC-ln-Line Extractor.
Type of Oil Grapefruithd Tangerine c,df Lemon a,c,e Lime a,b,e
No. of Samples 8 6 52 5

Max. Min. Max. Min. Max. Min. Max. Min.

Sp. gray. 25* C/25 C 0.8544 0.8506 0.8461 0.8457 0.8480 0.8500 0.8974 0.8642

Ref. ind. Nj 1.4767 1.4755 1.4743 1.4736 1.4749 1.4738 1.4907 1.4784

Ref. ind. 10% dist. N" 1.4718 1.4715 1.4725 1.4721 1.4731 1.4725 1.4732 1.4730

Difference 0.0050 0.0040 0.0019 0.0015 0.0018 0.0010 0.0177 0.0053

Opt. rot. a' +93.45 +91.52 +92.45 +91.56 +66.34 +57.82 +46.20 +39.85

Opt. rot. 10% dist. a' +97.61 +96.94 +96.01 +94.00 +65.34 +55.42 +51.71 +48.33

Difference +5.42 +3.60 +4.45 +1.55 -4.05 -1.28 +10.27 +3.53

Aldehyde content-% 1.56 0.98 1.17 1.12 3.66 1.99 6.66 4.70

Evaporative residue-% 8.60 5.93 4.30 3.63 2.60 1.60 16.67 4.66

SCD 0.32 0.19 0.68 0.50 0.48 0.20 1.23 0.99
UV spectrum
M log E 0.25g Peak 0.43 0.26 1.28 1.05 0.96 0.49 1.59 0.98
M log 100c
L MA 320 318 327.5 325.0 320 312 320 318

a Optical rotation at 200 C
b 1 mm light path
e 10 mm light path
d Aldehyde content-decyl
e Aldehyde content-citral
f Major UV peak only (minor peak occurs at 270 MU)


2.
a-
0
0
o^


--1







Table 6.-Maximum and Minimum Values for the Physical and Chemical Properties

Type of Oil Orange b Grapefruit b

No. of Samples 11 9


of Distilled Citrus Oils.

Tangerine b

2


Max. Min. Max. Min. Max. Min. Max. Min.



Sp. grave. 25 C/25 C 0.8464 0.8400 0.8539 0.8415 0.8415 0.8407 0.8596 0.8505


Ref. ind. N'o 1.4732 1.4715 1.4746 1.4714 1.4720 1.4716 1.4751 1.4742


Opt. rot. aD +98.56 +95.92 +96.50 +91.50 +93.07 +91.87 +52.60 +46.48


Aldehyde content-% 2.48 1.15 4.06 2.30 1.24 0.95 4.58 1.61


Ester content-% 1.38 0.22 2.52 0.08 0.35 0.25 3.49 1.75


Evaporation residue-% 1.24 0.08 3.66 0.19 0.55 0.20 1.70 0.18


a Optical rotation at 200 C
b Aldehyde content-decyl
c Aldehyde content-citral


00


Limea,c

10


h
0
2.


a
;;.




t?3


CT>
9
3.



I







By-Products of Florida Citrus


Table 7.-Physical and Chemical Properties of 10 Samples of Stripper Oil.

Stripper Oil Max. Min.

Specific gravity 25 C/25o C 0.8433 0.8398
Refractive index N2 1.4721 1.4713
Optical rotation a"2 +98.90 +95.55
Aldehyde content-% 1.50 0.47
Ester content-% 2.46 0.07
Evaporation residue-% 0.79 0.03



used in combination with the expressed oils to produce special
flavors or odors.
Citrus stripper oil contains over 95 percent of d-limonene,
and it is considered one of the purest sources for this mono-
cyclic terpene. A synthetic spearmint oil flavor, 1-carvone, has
been manufactured from this oil. Considerable quantities are
bought yearly for use as follows: a diluent in perfumes, flavors,
petroleum products, paint and varnish, rubber, and medicinals.
Newhall has described procedures for converting limonene into
diacetate, dipropionate, and dibutyrate esters (89) into several
new aminoalcohols (90) and stereospecific cis- and trans-epox-
ides (91). Patrick and Newhall (97) have shown further that
the aminoalcohols have useful fungicidal activity.


FLAVONOIDS
To date, more than 30 flavonoids have been found in the genus
Citrus, which is noted as an especially rich source of two im-
portant examples, hesperidin and naringin. Flavonoids are wide-
ly distributed in nature. At least 137 natural flavonoids are
known to occur in 153 genera of plants (129). They have been
subclassified also as flavones, flavanones, flavanols, isoflavones,
etc., all of which have a specific chemical configuration. There
is another small class of flavonoids, however, that have shown
physiological and biochemical activity. These compounds, such
as hesperidin, are classified now as bioflavonoids.
Since discovery in 1936 (109) that certain plant flavonoid
extracts had an unknown but curative factor not to be found in


39






Florida Agricultural Experiment Stations


other vitamins, there has been a profusion of literature on bio-
flavonoids sufficient to confound even trained minds. The term
vitamin P was suggested for the factor that improved capillary
fragility, but the dosage required in some tests suggested a
pharmacological action rather than that of a vitamin. In 1950,
it was recommended that the term vitamin P be discontinued.
Today, after years of study, there is still no specific chemical or
bioassay procedure for this biological factor, but its therapeutic
importance to many diseased capillary conditions has been recog-
nized. Citrus fruit continue to be regarded as an important
source of bioflavonoids.


Hesperidin
Abundant quantities of hesperidin are found in the blossom,
the small unripe fruit, and the peel of the mature sweet orange;
however, its exact function is not understood. It is found also
in lemons, mandarins, bitter oranges, and citrons. Each mature
sweet orange has almost 1 gram of hesperidin-like material of
which roughly half can be recovered by commercial procedures.
On this basis, 16 million pounds could have been recovered from
the oranges processed in Florida alone during the 1961-62
season. Domestic production, however, is of the order of 100,000
pounds annually (60).
Distribution in Sweet Oranges.-The proportion of hesperin-
din in the component parts of a mature orange were 32 to 50
percent in the rag and pulp, 30 to 50 percent in the albedo, 12
to 23 percent in the flavedo, and 1.5 to 6.0 percent in the juice
(51). A significantly greater amount has been found in the
stylar end than the stem end of the fruit (40).
There were only small differences between the hesperidin
content of Valencia, Hamlin, Parson Brown, and Pineapple
oranges throughout a season, although the last variety had the
most. During maturation, total hesperidin content reached a
near maximum before the fruit had an equatorial diameter of
2 inches.
Recovery of Hesperidin.--The easiest method of isolating
hesperidin is to extract chopped citrus peel with hot methanol,
and then allow it to crystallize as suggested by Horowitz (60).
Commercial practice, however, has found it more advisable to


40







By-Products of Florida Citrus


make an alkaline extraction with hydrated lime. The hesperidin
in chopped orange peel is dissolved slowly under alkaline condi-
tions that can be maintained by frequent hydrated lime additions.
After sufficient reaction time, the dilute hesperidin solution is
separated from the insolubles, is acidified, and is allowed to
crystallize. After a day or two, the crude product is filtered off
and dried. At least four patents (11, 57, 58, 59) have been
granted on this technique. Two products are produced for the
trade, hesperidin complex that has a minimum analysis of 40
percent and a purified product with a minimum assay of 90
percent hesperidin.
When extracting mature oranges, it was possible to recover
the equivalent of 8 to 10 pounds of pure hesperidin per ton of
peel residue. If, however, whole immature Valencia fruit of
1.2-inch average equatorial diameter are extracted, as much as
80 pounds of pure hesperidin per ton of fruit can be recovered
under the best conditions.
Experience has shown that better yields of hesperidin are
procured by recycling extraction liquid, by using Pineapple
orange peel, by chopping the peel finely, and by extracting im-
mature fruit. The ideal extracting pH was highest for immature
fruit and proportionately lower with fruit of more advanced
maturity. Effective extraction required a minimum pH of 11.1.
Hesperidin isolated by commercial procedures varied in purity
between 90 and 39 percent, being greatest with the most imma-
ture fruit. Highest purity was obtained by those conditions that
encouraged best yield.
Purification.-Hesperidin can be purified readily by recrys-
tallizing from a formamide solution (100) but is purified com-
mercially by dissolving the crude product in an alkaline alcohol
water solution. A 50 percent isopropyl alcohol concentration
was the most effective compromise for best filtration rate and
hesperidin recovery. The purified product is isolated by subse-
quently acidifying, crystallizing, and filtering. Optimum crys-
tallizing pH was 8.5.
The recovery of hesperidin was improved significantly by
extending the crystallization period (52), but the additional
time required could be impractical. If product purity required
improvement, it was improved sufficiently by washing or by
reslurrying the crystallized product with volumes of very hot
water.


41







Florida Agricultural Experiment Stations


Analysis.-The Davis method (27) is the analytical method
most often used for hesperidin products. Although insufficiently
specific, it is as adequate as other methods. When eight analyt-
ical techniques for hesperidin and other flavonoids were evalu-
ated (46), the Lorenz and Arnold (82) procedure was found to
be unsuited, while the authors' azo-coupling method (46) was
the most sensitive. A methoxy test (6) was sometimes useful,
as was the gravimetric procedure (19). The Arcangeli-Trucco
method (4) was the most tedious, while a UV technique (50)
was the most specific of the photometric procedures. Paper
chromatography was very specific but lacked sensitivity. It was
concluded that the Davis method offered more advantages in
routine assaying. This determination was more sensitive, how-
ever, when modified to a lower wave length.
The bioassay of hesperidin and other flavonoid extracts cap-
able of improving capillary permeability has been carried out
with many different animals. The guinea pig has been the most
satisfactory animal, although even it was not entirely adequate
(10). Less accepted than the animal tests, whiph are unsuited
to routine analysis, have been the alternative short-cut methods
of biological assay, such as: measuring bleeding time, inhibition
of succinoxidase or hyaluronidase, toxicity protection against
arsenicals, and others mentioned by Scarborough et al. (110).
Uses.-Hesperidin has found its greatest use as a therapeutic
agent in the pharmaceutical industry. Toward this same end,
patents were granted for the conversion of hesperidin to a car-
boxylate derivative by Ohta (96), to an alkylated chalcone by
Wilson (130), to a water-soluble alkoxyl substituted chalcone
glycoside by Wilson (131), and to a methylene carboxy chalcone
by Hart (42). Patents were granted to the authors (48) for the
preparation of an azo dyestuff and to Toulmin (118, 119) for
conversion to azo dye wood stains.
Hesperidin has important therapeutic use as an animal feed
supplement, but insufficient data have been published to date.


Naringin
Similar to the hesperidin of oranges, naringin occurs as the
predominant flavonoid in the grapefruit (Citrus paradisi Mac-
Fayden) and in the less seen shaddock or pummelo (Citrus
grandis [Linn.] Osbeck). Naringin is distinguished readily from


42







By-Products of Florida Citrus


hesperidin by its extreme bitterness, which is imparted some-
times to grapefruit products. Several million pounds of naringin
occur in the annual Florida harvest of grapefruit, but almost
none is recovered.
Distribution in Grapefruit.-The distribution of naringin on
a percentage basis in the component parts of mature grapefruit
was: 50 to 60 percent in the albedo, 30 to 40 percent in the rag
and pulp, 5 to 10 percent in the flavedo, and 1 to 3 percent in
the juice (72). More naringin was found in the seedy grape-
fruit varieties, but only by virtue of their larger size.
Recovery of Naringin.-Naringin can be recovered by meth-
ods similar to those for hesperidin. When alkali is used to solu-
bilize the naringin, a lower pH (8.8 to 9.0) is needed than when
recovering hesperidin. If the grapefruit peel is sufficiently im-
mature, it is possible to release 80 to 90 percent of the recover-
able naringin with a plain water extraction. Extracts are treated
later with alkali to degrade the pectin that inhibits naringin
crystallization. The water-extracted peel is ideally suited for
the further recovery of pectin.
When immature whole Marsh grapefruit is extracted, the
equivalent of 52 pounds of pure naringin can be recovered per
ton of fruit. Fruit in this special case should have an equatorial
diameter not greater than 1.5 inches. Peel of mature grapefruit
can yield the equivalent of 4 to 8 pounds of naringin per ton.
There are, however, more problems in crystallizing naringin
than hesperidin, and yields are often disappointing.
Purification.-Crude naringin is purified most easily by the
authors' procedure (53) of dissolving the crude naringin in
boiling anhydrous isopropanol. The concentrated naringin solu-
tion (approximately 9 percent) is filtered from its insolubles
and is allowed to crystallize. Seeding is required sometimes. The
crystallized naringin is separated by filtering and is washed with
more isopropanol before drying. A purified naringin of 98 to
100 percent purity is produced by this technique. Solvent costs
are reduced by recycling extraction alcohol without much loss
in product purity.
Analysis.-The analytical techniques for naringin closely
resemble those for hesperidin. A comparison of the sensitivity
of the more common analytical techniques has been published
by the authors (46).


43







Florida Agricultural Experiment Stations


Uses.-The characteristic bitter taste of naringin has been
used to advantage in the preparation of beverage drinks and to
enhance the piquant flavor of high class confections. Pulley et al.
(102) have described a procedure for recovering the valuable
rhamnose fraction of the molecule, while the authors have a
patent (48) on the manufacture of azo dyes from it. Today
naringin production is minute, but naringin has been sold com-
mercially under the name "Amerin."


Miscellaneous
S Recently, attention has been given to some of the less known
flavonoids of citrus. Jones et al. (64) have reported that the
natural flavonoid tangeretin has very high cytostatic potency
against the zebra fish embryo, while Freedman and Merritt (36)
have demonstrated that nobiletin possesses strong anti-inflam-
matory activity. Both compounds have shown promise in cancer
research studies. Tangeretin and nobiletin are known to occur
in tangerines (Citrus reticulata Blanco) (60), and nobiletin
was found also in peel of Valencia orange (116).
For many years, quantities of citrus molasses have been
solvent-extracted to yield a concentrate which is refined to a
dried, therapeutically active product. It is sold in the pharma-
ceutical trade, and according to one related patent (114) is a
biofiavonoid mixture of three substances similar to quercitrin,
eriodictyol, and hesperidin.


CITRUS SEED OILS
In 1938-39, the production of citrus seed oil was 45 tons, and
it was estimated that approximately 2,000 tons total could have
been recovered (93). During the next 20 years, interest in citrus
seed oil dropped and production declined. In the last few years,
annual production has increased to about 1,500 tons. By virtue
of the greater attention devoted to diets containing higher quan-
tities of unsaturated fats as are present in vegetable seed oils,
interest in citrus seed oils has flourished. In the foreseeable
future, production of a standardized dried citrus pulp having a
uniform quantity of seeds is likely. This would make available
larger quantities of grapefruit and orange seeds to process, thus
establishing this industry more firmly. On the basis of boxes


44







Florida Agricultural Experiment Stations


Uses.-The characteristic bitter taste of naringin has been
used to advantage in the preparation of beverage drinks and to
enhance the piquant flavor of high class confections. Pulley et al.
(102) have described a procedure for recovering the valuable
rhamnose fraction of the molecule, while the authors have a
patent (48) on the manufacture of azo dyes from it. Today
naringin production is minute, but naringin has been sold com-
mercially under the name "Amerin."


Miscellaneous
S Recently, attention has been given to some of the less known
flavonoids of citrus. Jones et al. (64) have reported that the
natural flavonoid tangeretin has very high cytostatic potency
against the zebra fish embryo, while Freedman and Merritt (36)
have demonstrated that nobiletin possesses strong anti-inflam-
matory activity. Both compounds have shown promise in cancer
research studies. Tangeretin and nobiletin are known to occur
in tangerines (Citrus reticulata Blanco) (60), and nobiletin
was found also in peel of Valencia orange (116).
For many years, quantities of citrus molasses have been
solvent-extracted to yield a concentrate which is refined to a
dried, therapeutically active product. It is sold in the pharma-
ceutical trade, and according to one related patent (114) is a
biofiavonoid mixture of three substances similar to quercitrin,
eriodictyol, and hesperidin.


CITRUS SEED OILS
In 1938-39, the production of citrus seed oil was 45 tons, and
it was estimated that approximately 2,000 tons total could have
been recovered (93). During the next 20 years, interest in citrus
seed oil dropped and production declined. In the last few years,
annual production has increased to about 1,500 tons. By virtue
of the greater attention devoted to diets containing higher quan-
tities of unsaturated fats as are present in vegetable seed oils,
interest in citrus seed oils has flourished. In the foreseeable
future, production of a standardized dried citrus pulp having a
uniform quantity of seeds is likely. This would make available
larger quantities of grapefruit and orange seeds to process, thus
establishing this industry more firmly. On the basis of boxes


44







By-Products of Florida Citrus


of seedy fruit processed (35), it is estimated that a theoretical
potential of 14,720 tons of seed oil could have been recovered
in the 1961-62 season.
In Florida, citrus seed oil is produced from a mixture of
predominantly grapefruit and smaller quantities of orange seeds
accumulated in making citrus sections and citrus salads. Since
no citrus processing plant is sufficiently large to economically
operate a seed oil recovery system, many processors segregate
their wet seeds, which are dried and processed for their oil
content at one centrally located plant.


Processing Procedure
Citrus seeds are separated from the peel, rag, and pulp or
carpellary membranes and juice vesicles of sectionized fruit by
dropping the discarded residue into a rotating reel fixed with a
coarse screen. The finer material, such as the seeds and juice
vesicles, falls through the openings. A paddle finisher separates
juice vesicles and bits of citrus rag from the seeds. The recovered
seeds are conveyed into a truck, transported, washed with a lime
.slurry, and dried to less than 8 percent moisture in a direct fired
drier. The dried seeds may or may not pass through a roller mill
(Fig. 11) to flake and break apart the hulls, which are removed
by screens. Depending on the previous step, the kernels or whole
seeds are pressed mechanically at high pressures in an oil ex-
peller (Fig. 12). This operation is carried out at carefully chosen
elevated temperatures to avoid changes to a technical grade. A
turbid oil is recovered that is clarified in a plate and frame
press.
Solvent extraction of citrus seed oil is not practiced today in
Florida, nor is refining, bleaching, deordorizing, and wintering.
Citrus seed oil is not recovered presently in quantities large
enough to justify a solvent extraction plant, and for the same
reason the oil is usually sold on an unrefined basis. This oil is
not changed noticeably in appearance by refining, but it does lose
the extremely bitter taste that at one time almost precluded
further consideration of the product. Refining is carried out by
treating the seed oil with strong sodium hydroxide solution in
a ratio that is calculated from analysis of the free fatty acid
content. The mixture of alkali and oil is stirred and warmed, and
the emulsion so formed, breaks in about 10 minutes at 45 C.


45







Florida Agricultural Experiment Stations


Fig. I I.-A roller mill. (Picture taken at Imperial Citrus By-Products, Inc.,
Lakeland.)


The precipitated material, known as foots or soap stock, is
separated by prolonged gravity settling. Bleaching or decoloriz-
ing is carried out at temperatures slightly above 100 C with
Fuller's Earth, bleaching clays, or in some cases, activated
carbon.
Winterizing is an occasional practice. It involves chilling and
pressing the seed oil at approximately 1 C. More saturated
fatty acids than unsaturated ones are lost in the process, and
specific gravity, refractive index, and iodine number increase,
as shown by Nolte and von Loesecke (93).
Virtually all edible vegetable oils, with the exception of
olive oil, are subjected to a deodorizing treatment for off-flavor
and odor removal. It is invariably the last step and essentially
involves a steam distillation at elevated temperatures to remove
the volatile impurities responsible for off-flavor and odor. There
is a concurrent reduction in color and quantity of free fatty
acids.


46







By-Products of Florida Citrus


Chemical Composition
When seed oil is to be manufactured, the seediness of the
different varieties of citrus processed in Florida becomes quite
important. Fortunately, the more seedy grapefruit are used for
citrus sections and salads. A comparison of the percentage of
seeds in the different varieties of orange and grapefruit during
the normal processing period is shown in Table 8. In the later
stages of maturation the percentage of seeds by weight in citrus
is markedly influenced by fruit maturity. Fruit weight increases
during this period at a greater rate than seed weight and brings
about a constantly decreasing percentage of seeds in the fruit.
In many instances there were also a fewer number of developed
seed in the fruit picked at the end of the season. Although there
were some inconsistencies, the seeds of all citrus varieties de-
creased in moisture content as they matured. The calculated
percentages of seeds and seed oil obtained from dried citrus
pulp made from different citrus fruit residues are shown also
in Table 8. The important citrus selections for seed oil produc-
tion are shown by Table 8 to be 'Duncan', or seedy grapefruit,
and two orange varieties, Pineapple and Parson Brown.
Percentage of oil in dried citrus seeds is variable and de-
pendent upon fruit maturity. Typically, the oil content of dried
Pineapple orange seeds varied from 30.2 percent to 45.2 percent,
while oil content of dried Duncan seeds varied from 29.2 percent
to 37.3 percent. Highest oil content usually coincided with the
optimum maturity needed for processing. Van Atta and Dietrich

Table 8.-Seed and Oil Data of Citrus Varieties Before and After Processing to
Dried Citrus Pulp.

Dried Citrus Pulp
Fresh Fruit (8% Water)
Moisture in
Variety Seeds % Seeds % Seeds % Seed Oil %

Hamlin 0.45 56 2.4 0.9
Parson Brown 2.3 54 12.2 4.5
Pineapple 2.7 50 14.3 5.3
Valencia 0.8 48 4.3 1.6
Duncan 4.4 58 17.7 5.4
Marsh 0.25 56 1.0 0.3


47











VERTICAL MOTOR


"n


N



0
7-"
I0






0.
0
o





0


0.








0
3

x















_n
2.


C3.




C."
Cn











Table 9.-Physical and Chemical Properties of Various Citrus Seed Oils.

Seed Oil of
Determination Grapefruit (93)a Lemon (1)a Lime (1)a Orange (32)a Tangerine (117)a

Specific gravity 25 C/25 C 0.9197 0.914-0.917 0.917-0.919 0.916-0.920 0.9165
Refractive index N C 1.4698 1.471-1.472 1.467-1.475 1.468-1.470 1.4702
Iodine value 100.9 103-110 101-111 98-104 107.3
Saponification value 193 188-196 193-198 192-197 194
Unsaponifiable matter, % 0.48 Below 1 Below 1 0.4-1.0 0.5
Titer C 32-38 34-35 34-35 -
Acetyl value 2.4 13-33 2-11 8.2
Reichert-Meissl value 0.47 Below 0.5 Below 0.5 0.5 max. -
Polenske value 0.20 Below 0.5 Below 0.5 0.5 max.

a Numbers in parentheses refer to Literature Cited.







Florida Agricultural Experiment Stations


(123) found 34.2 percent oil in dry Valencia orange seeds; the
kernels alone had 55 percent oil. The oil contents of grapefruit,
lime, lemon, and orange seeds were stated by Jamieson (63) to
be respectively 30 percent, 31 to 40 percent, 30 to 35 percent,
and 40 to 45 percent.
Some of the physical and chemical characteristics that have
been determined for citrus seed oils are shown in Table 9. Each
determination has significance and sometimes can furnish a
criterion for distinguishing seed oils of the different Citrus
species, such as shown in Fig. 13. This scatter diagram of
iodine number and index of refraction values for citrus seed
oils was compiled from the authors' published (47, 49, 54) and
unpublished analyses. Specific gravity, refractive index, and
titer, the constants shown in Table 9, are measured readily and
relate respectively to density, refraction of light, and melting
point. The other values in Table 9 are chemical determinations,
iodine value measuring unsaturation, saponification value relat-
ing to molecular weight, unsaponifiable matter being the per-
centage of oil not affected by the saponifying alkali, and acetyl
value being a measure of the number of free hydroxyl groups.
Reichert-Meissl and Polenske values relate respectively to the



.471 CITRUS SEED OILS

0
Lemon

C
S1.470 Mandarin

0
o o
o 0o Grapefruit
I 1.469- 4 eo
r 0 0oo


Iodine Value


Fig. 13.-Relation between iodine value and refractive index for seed oils from
various Citrus species.


50







By-Products of Florida Citrus


quantity of soluble and insoluble volatile acids present after
saponification.
Citrus seed oil is composed mainly of a mixture of fatty
acids esterfied with glycerol, as are most all vegetable oils. It
can be distinguished from the others, however, by the absence
or presence of certain fatty acids or by the proportional differ-
ences in fatty acid content. The composition of citrus seed oils
is shown in Table 10. This analysis draws attention to why
citrus seed oil has been classified by some as a linolenic acid oil
and by others as one that is rich in both oleic and linoleic acids.
Citrus seeds are recognized as also being a valuable source
of protein. The nutrient composition of a mixture of grapefruit
and orange seeds is shown in Table 11. In this analysis, the


Table 10.-Comparison of the Average Fatty Acid Composition of Seed Oils from
Many Species of Citrus.
Fatty Acid Distribution %
Seed Oil of Palmitic Stearic Oleic Linoleic Linolenic

Orange 31 4.2 26 36 2.8
Grapefruit 34 3.4 22 37 4.6
Tangerine 31 3.4 21 39.9 4.7
Key lime 31 4.3 20 35 9.7
Persian lime 28.8 4.9 22.1 39.1 5.1
Lemon 26 2.8 27 33 11.2
Calamondin 24.5 5.1 36.7a 28.2 5.3
a Includes 5.1% palmitoleic acid.


Table 11.-Average Composition of Citrus Seeds, Seed Hulls, and Kernels (2).
Seed Component %
Extracted Extracted
Analysis Whole Hull Kernel Whole a Kernel a
Moisture 0.0 0.0 0.0 10.0 10.0
Crude fat (E.E.) 45.1 2.3 59.2 0.0 0.0
Protein (N x 6.25) 16.2 6.1 19.5 26.5 43.0
Crude fibre 13.2 48.1 3.1 22.1 6.8
Ash 3.4 4.4 2.8 5.6 6.2
N-free extract 22.1 39.1 15.4 35.8 34.0
a Calculated.


51







Florida Agricultural Experiment Stations


hulls constituted 27 percent of the citrus seed mixture. The
separated seed kernel was found by Ammerman et al. (2) to
have almost 60 percent oil content. After being extracted, it
had more than 40 percent protein by Kjeldahl analysis. The ash
constituents of citrus seeds and seed press cake are mainly
magnesium, potassium, calcium, and phosphorus, according to
Nolte and von Loesecke (93).


Utilization of Citrus Seed Oil, Meal, and Hulls
The flavor of a refined citrus seed oil resembles greatly that
of olive oil, for which it sometimes has been substituted. It is
pale yellow in color, considered wholesome and well suited for
food, and has been used most successfully as a cooking oil and
salad oil. In addition, citrus seed oil can be hydrogenated to
become a butter substitute or cooking fat. Somewhat similarly,
it can be brominated to secure a high specific gravity oil (ap-
proximately 1.30), which is used by the beverage industry to
adjust the density of flavoring oils added to beverages. Bromi-
nated citrus seed oil is competitive with other brominated oils,
such as apricot kernel seed oil and sesame oil.
Citrus seed meal was shown by Glasscock et al. (39) to be
as valuable as cottonseed meal in meeting the protein require-
ments of growing steers being fattened. However, it was harm-
ful to swine when fed at levels as low as 10 percent of the total
ration. When the protein of dried citrus meal was compared
to that of soybean meal by feeding lambs a ration having 88
percent of the total protein supplied by either dried citrus meal
or soybean meal, they were equal in digestibility and biological
value. The average apparent digestibility of the protein in
citrus seed meal was 55.5 percent in this trial. Dried citrus seed
meal has been tested in poultry rations also, but was found to
have a factor that was toxic to chickens (31). The toxic factor
can be removed by solvent extraction and was identified as
limonin, the bitter principle in the seed (31).
Presently, citrus seed meal is usually blended with dried
citrus pulp for cattle feed. The hulls are sold usually to fertilizer
plants as a conditioner. However, the approximate composition
shown by Ammerman et al. (2) suggests citrus seed hulls to be
similar in value to cottonseed hulls and to be equally as valuable
in a livestock feeding program.


52







By-Products of Florida Citrus


PECTIC SUBSTANCES
Approximately 5 million pounds of pectin are recovered an-
nually from citrus for use by food processors in the United
States, according to one recent estimate (108). Today, none
is recovered in Florida, despite a potential of 90 million pounds
available in processed citrus peel residue.
Pectin occurs naturally in all fruit, but is present abundantly
in citrus fruits. It is found in three forms; pectic acid (con-
taining no methoxy groups), pectinic acid or pectin (capable of
forming gels), and protopectin (the acid-hydrolyzable parent
substance). These pectic substances occur in all plant tissues
and are characterized chemically by the presence of a galac-
turonic acid nucleus in the molecular structure.
The pectin molecule is thought by present view to consist
largely, if not entirely, of a long chain of varying length of par-
tially methylated galacturonic acid units. The characteristics of
a pectin are determined by molecular size, degree of esterifica-
tion, and amount of accompanying material. Only the pectinic
acids have commercial value, due primarily to their jellying
properties, their colloid stabilizing properties, and their power
of water imbibition (37).
Since pectin is such a variable substance, it is often meaning-
less to mention only quantity of percentage of pectin without
evaluating methoxyl content, gelling power, purity, degree of
polymerization, and viscosity. The most meaningful term be-
comes the jelly unit, obtained by multiplying the percentage
recovery of pectin and its gelling capacity or grade.
In studying the pectin content of Florida grapefruit and
oranges, Gaddum (37) found: 1, the percentage of total pectic
compounds in the albedo and pulp remains constant over much
of the growth period; 2, the percentage of water-soluble pectins
rises in these tissues to a maximum just prior to the decline
in total pectic content; and 3, the rate of protopectin conversion
into water-soluble pectins is greater in the pulp than the albedo.
California grapefruit peel and rag contained 3.93 percent pectin
as calcium pectate according to Poore (99). His individual
analyses of Florida peel and rag showed, respectively, 3.19 and
3.56 percent pectin as calcium pectate.
Pectin, as calcium pectate, was determined on a wet and dry
basis by Rouse (104) in the component parts of seven varieties
of mature citrus fruits. On a dry basis, the rag component had


53







Florida Agricultural Experiment Stations


the highest percentage of pectin in 'Dancy' tangerine, Pineapple
and Valencia oranges, and Duncan grapefruit. Only in the
Hamlin and 'Temple' oranges was the albedo the most abundant
source of pectin, while 'Marsh' grapefruit was unusual in having
the highest percentage pectin in the flavedo.
The effects of maturity upon the physical and chemical values
of extracted pectins from peel, membrane, and juice sacs of
Valencia oranges were investigated by Rouse et al. (108) in a
more recent study. Since water-soluble pectin fractions always
were included, there were only minor maturity differences.
The pectins extracted from the membrane fraction were highest
in yield, jelly grade, purity, and relative viscosity. Jelly grade
for the extracted pectins decreased slightly with maturation,
but increased later. The average jelly grade for peel, membrane,
and juice sacs was 206, 314, and 222 respectively. Pectins from
the seeds had no jelly grade.
Recently, the pectin content of Valencia (106) and Pineapple
(107) oranges of Florida has been studied in even greater detail
by Rouse et al. The percentage of pectin found to be water-
soluble, ammonium oxalate-soluble, and sodium hydroxide-soluble
was determined for five components of each variety at different
stages of maturity during two seasons. It was found that the
ammonium oxalate-soluble pectin content of the Valencia orange
components increased slightly during maturation. The trend
was not detected in Pineapple oranges. Protopectin was greatest
in the membrane component of each variety and generally de-
creased in the latter part of the sampling period. The five com-
ponents into which fruit were separated for study were peel,
membrane, juice sacs, seeds, and juice. The average proportions
by weight of these components in Pineapple oranges were,
respectively, 22.7, 14.2, 21.9, 3.5, and 37.7. The proportions for
Valencia oranges were 20.8, 12.0, 23.7, 0.8, and 42.7 respectively.
The membrane fraction of Pineapple and Valencia oranges
has such a high percentage of excellent grade pectin that this
component seems ideally suited for pectin manufacture. When
oranges are commercially extracted, it is possible to segregate
the residue into two fractions, the first containing membrane,
juice sacs, and seeds and the second containing only peel. If
these fractions were separated, the collection of seeds would be
simplified, a membrane portion could be retrieved that is suited
for pectin recovery, and there would be less fines burned in the
production of dried citrus pulp.


54







By-Products of Florida Citrus


Pectin Pomace
A refined pectin pomace of better than 50 grade can be pro-
duced readily from citrus peel residue. The product is used by
jam, jelly, and marmalade manufacturers. Although the peel
residue must be scalded, leached, pressed and dried, considerably
less elaborate equipment is required than for manufacturing
powdered pectin.
Although pectin pomace is not manufactured today in Florida,
it was made in 1944 (3) by methods that have been described
by Pulley and co-workers (103). The process begins with the
residue from extracted grapefruit. Seeds are removed by tum-
bling the residue in a wire cage. Pectic enzymes are inactivated
and water-soluble impurities removed from the peel residue by
shredding and mixing it with boiling water. Further dilution
with cold water quickly reduces the temperature, whereupon
the mixture is revolved in a straining drum to remove as much
water as possible. The chopped peel is leached two additional
times with cold water, and sometimes aluminum sulphate is
added in the last leach. As much liquid as possible is removed
from the pomace, as it is now called, by pressing. The pressed
pomace is dried to 4 to 8 percent moisture and is ground to
pass a 20 mesh screen. Hard water was found detrimental to
the process, while aluminum sulfate was helpful in aiding the
removal of water by pressing, although it did not improve
jelly grade of the pomace.

Juice Sacs and Other Products
The juice sacs or pulp screened from the citrus juices are
good bases for making many food products, such as jams, pie
fillings, ice cream, sherbets, sundae topping, and beverage bases,
according to Singleton (113), provided extraneous matter is
removed. Extraneous matter can be removed by washing the
juice sacs in a flotation V-trough having water jets aimed from
above to strike the floating pulp. Excess water is eliminated
afterwards by a vibrating screen. The pulp or juice sacs can
be used immediately, frozen for later use, or canned if pasteurized
quickly.
Citrus peel residue is the source for another product, called
pecticell. The material is essentially pectin and cellulose, is used
as a filler for plastics, and has been made in pilot plant quanti-
ties by drying finely ground citrus peel that has first been leached


55







By-Products of Florida Citrus


Pectin Pomace
A refined pectin pomace of better than 50 grade can be pro-
duced readily from citrus peel residue. The product is used by
jam, jelly, and marmalade manufacturers. Although the peel
residue must be scalded, leached, pressed and dried, considerably
less elaborate equipment is required than for manufacturing
powdered pectin.
Although pectin pomace is not manufactured today in Florida,
it was made in 1944 (3) by methods that have been described
by Pulley and co-workers (103). The process begins with the
residue from extracted grapefruit. Seeds are removed by tum-
bling the residue in a wire cage. Pectic enzymes are inactivated
and water-soluble impurities removed from the peel residue by
shredding and mixing it with boiling water. Further dilution
with cold water quickly reduces the temperature, whereupon
the mixture is revolved in a straining drum to remove as much
water as possible. The chopped peel is leached two additional
times with cold water, and sometimes aluminum sulphate is
added in the last leach. As much liquid as possible is removed
from the pomace, as it is now called, by pressing. The pressed
pomace is dried to 4 to 8 percent moisture and is ground to
pass a 20 mesh screen. Hard water was found detrimental to
the process, while aluminum sulfate was helpful in aiding the
removal of water by pressing, although it did not improve
jelly grade of the pomace.

Juice Sacs and Other Products
The juice sacs or pulp screened from the citrus juices are
good bases for making many food products, such as jams, pie
fillings, ice cream, sherbets, sundae topping, and beverage bases,
according to Singleton (113), provided extraneous matter is
removed. Extraneous matter can be removed by washing the
juice sacs in a flotation V-trough having water jets aimed from
above to strike the floating pulp. Excess water is eliminated
afterwards by a vibrating screen. The pulp or juice sacs can
be used immediately, frozen for later use, or canned if pasteurized
quickly.
Citrus peel residue is the source for another product, called
pecticell. The material is essentially pectin and cellulose, is used
as a filler for plastics, and has been made in pilot plant quanti-
ties by drying finely ground citrus peel that has first been leached


55







56 Florida Agricultural Experiment Stations

with water and solvents. Over-all costs were found to be high.
Another product, orange flour, has shown promise as a water-
thickening agent in fire retardant mixtures for fighting forest
fires. Orange flour is produced by pulverizing the drum-dried
citrus juice sacs and pulp that have been successively finished,
washed, and refinished. It is a by-product of the pulp washing
procedure used to recover additional soluble solids in the manu-
facture of orange concentrate. Approximately 8 pounds of wet,
processed pulp can be recovered per box of fruit.

Utilization
Pectic substances have their widest use in jams, jellies, and
marmalades. However, pectins can be used to coagulate the
casein of milk or to improve the quality of bread and bakery
products. They are used extensively in the manufacture of
confections and as an emulsifying agent in salad dressings and
mayonnaise. In addition, pectins have found use in other food
products-in ice cream, as a glazing agent for dried or candied
fruit, and as coatings for several kinds of other foods. Uses
for pectin have been described more fully by Kertesz (66), who
writes of the further use of pectins in wound treatment as a
hemostatic agent, as a blood plasma substitute, as a treatment
for gastrointestinal disturbances, in pastes, cosmetics and soaps,
for quenching of steel and other alloys, for making pectinate
films and fibres, and for many other uses.


FOOD PRODUCTS
Brined and Candied Peel
For an unknown number of years, curing and preserving
citrus peel with brine has been a well established practice in
other citrus growing regions of the world. In Florida, the prac-
tice is quite limited and is used primarily to preserve the peel
for candying at a later date.
Fruit that are bright and free from scale, melanose, or wind
scaring are ideal for this purpose and preferably should be ream-
ed to a clean half-cup containing a minimum of rag. According
to one source (120), these cups of peel are washed, nested
in 52-gallon fir barrels, and completely covered with a 10 per-
cent salt solution. The brine solution is maintained at a 10 per-







56 Florida Agricultural Experiment Stations

with water and solvents. Over-all costs were found to be high.
Another product, orange flour, has shown promise as a water-
thickening agent in fire retardant mixtures for fighting forest
fires. Orange flour is produced by pulverizing the drum-dried
citrus juice sacs and pulp that have been successively finished,
washed, and refinished. It is a by-product of the pulp washing
procedure used to recover additional soluble solids in the manu-
facture of orange concentrate. Approximately 8 pounds of wet,
processed pulp can be recovered per box of fruit.

Utilization
Pectic substances have their widest use in jams, jellies, and
marmalades. However, pectins can be used to coagulate the
casein of milk or to improve the quality of bread and bakery
products. They are used extensively in the manufacture of
confections and as an emulsifying agent in salad dressings and
mayonnaise. In addition, pectins have found use in other food
products-in ice cream, as a glazing agent for dried or candied
fruit, and as coatings for several kinds of other foods. Uses
for pectin have been described more fully by Kertesz (66), who
writes of the further use of pectins in wound treatment as a
hemostatic agent, as a blood plasma substitute, as a treatment
for gastrointestinal disturbances, in pastes, cosmetics and soaps,
for quenching of steel and other alloys, for making pectinate
films and fibres, and for many other uses.


FOOD PRODUCTS
Brined and Candied Peel
For an unknown number of years, curing and preserving
citrus peel with brine has been a well established practice in
other citrus growing regions of the world. In Florida, the prac-
tice is quite limited and is used primarily to preserve the peel
for candying at a later date.
Fruit that are bright and free from scale, melanose, or wind
scaring are ideal for this purpose and preferably should be ream-
ed to a clean half-cup containing a minimum of rag. According
to one source (120), these cups of peel are washed, nested
in 52-gallon fir barrels, and completely covered with a 10 per-
cent salt solution. The brine solution is maintained at a 10 per-







56 Florida Agricultural Experiment Stations

with water and solvents. Over-all costs were found to be high.
Another product, orange flour, has shown promise as a water-
thickening agent in fire retardant mixtures for fighting forest
fires. Orange flour is produced by pulverizing the drum-dried
citrus juice sacs and pulp that have been successively finished,
washed, and refinished. It is a by-product of the pulp washing
procedure used to recover additional soluble solids in the manu-
facture of orange concentrate. Approximately 8 pounds of wet,
processed pulp can be recovered per box of fruit.

Utilization
Pectic substances have their widest use in jams, jellies, and
marmalades. However, pectins can be used to coagulate the
casein of milk or to improve the quality of bread and bakery
products. They are used extensively in the manufacture of
confections and as an emulsifying agent in salad dressings and
mayonnaise. In addition, pectins have found use in other food
products-in ice cream, as a glazing agent for dried or candied
fruit, and as coatings for several kinds of other foods. Uses
for pectin have been described more fully by Kertesz (66), who
writes of the further use of pectins in wound treatment as a
hemostatic agent, as a blood plasma substitute, as a treatment
for gastrointestinal disturbances, in pastes, cosmetics and soaps,
for quenching of steel and other alloys, for making pectinate
films and fibres, and for many other uses.


FOOD PRODUCTS
Brined and Candied Peel
For an unknown number of years, curing and preserving
citrus peel with brine has been a well established practice in
other citrus growing regions of the world. In Florida, the prac-
tice is quite limited and is used primarily to preserve the peel
for candying at a later date.
Fruit that are bright and free from scale, melanose, or wind
scaring are ideal for this purpose and preferably should be ream-
ed to a clean half-cup containing a minimum of rag. According
to one source (120), these cups of peel are washed, nested
in 52-gallon fir barrels, and completely covered with a 10 per-
cent salt solution. The brine solution is maintained at a 10 per-







By-Products of Florida Citrus


cent salt content until the peel is cured, which is judged by
appearance. When peel is translucent but not mushy or mealy,
it is covered by a fresh 15 percent brine solution and is ready
for storage. Quite often, 500 to 600 ppm of sulfur dioxide is
added.
Alternatively, citrus peel can be preserved for later candying
by tray-drying the half cups (or diced peel) at moderate
temperatures. Preliminary experience has shown that this type
peel reconstitutes well, candies without toughness, and avoids
the sulfur dioxide bleaching effect. The high drying costs are
offset by the cheaper storage.
Candied citrus peel is made from either fresh or brined
peel. Fresh peel, free of blemishes, is sought and must be cook-
ed until tender, with the water changed sufficiently to remove
some of the bitterness and portions of the peel oil. At times,
the peel is roughened to help release excess peel oil. Brined peel
is soaked in hot or cold water, depending on thickness of peel,
to remove the salt prior to candying.
The tenderized peel from either process is drained, diced, and
immersed in a sugar syrup made from mixtures of sucrose and
dextrose. Sugar concentration is increased gradually over many
days to approximately 50 Brix to permit thorough penetration
of sugars. The partially candied peel is cooked finally with a
more concentrated sugar solution (76 Brix) to complete the
candying operation. Food colors are added during the candying
operation to impart pleasing colors to the product. The candied
peel is finally drained, dried, and dusted with powdered sugar
or corn starch. Candied peel is prepared sometimes by a so-
called "quick process." Tenderized peel is cooked with a low
Brix sugar syrup that penetrates the peel and increases in con-
centration by evaporation over a short span of time. Cooking
tenderized peel with a sugar syrup in a vacuum allows it to
be candied in 30 to 40 minutes. Breaking the vacuum inter-
mittently, during the cooking, prevents the formation of bubbles
in the candied peel. The lower cooking temperature imparts a
better color to the product.


Marmalades
There are as many different ways to make marmalade as
there are manufacturers of the product, and formulas are pub-


57







Florida Agricultural Experiment Stations


lished in abundance. Federal grades and standards for orange
marmalade (122) require the sweet orange product to be com-
posed of not less than 30 parts of fruit to 70 parts of sugar.
Bitter orange marmalade should contain not less than 25 parts
of fruit to 75 parts of sugar. It is stipulated further that peel
be evenly distributed, of uniform size, and in substantial but
not excessive amount. In order to gel properly, marmalade re-
quires about 0.5 percent high grade pectin, usually 65 percent
sugar, and sufficient citric or other acid to adjust the pH be-
tween 3.0 and 3.4.
Each year, commercial manufacturers utilize considerable
quantities of citrus peel, especially orange, in marmalade pro-
duction. Usually they prepare a base or stock for later process
ing. Bitter orange marmalade base is prepared commercially
(105) by mechanically peeling the fruit and heating the juice
to 195 F. The seeds and coarse pulp are removed by a finisher.
The peel, including most of the albedo portion, is delivered from
the peeler in quarters. This is cooked, cooled, cut into thin
strips, and mixed with the finished juice. The product is stand-
ardized with water, barrelled, and stored at refrigerated tem-
peratures or sulfited for storage at ambient temperatures. Tech-
niques for preparing clear and cloudy type marmalades were
reviewed recently (120), and the authors discussed the option
of using orange concentrate and dehydrated citrus peel in mar-
malades.
The occasional pregelation of commercial packs of bitter
orange marmalade bases was investigated by Rouse (105) and
found to be caused by pectinesterase activity and low pH con-
ditions. Pregelation in storage is corrected by adjusting the
barrelled product to pH 4.0 and treating with Pectinol M.


Bland Syrup
Currently, the Florida citrus industry consumes approxi-
mately 10 million pounds of sugar to sweeten single-strength
juices and canned grapefruit sections. Of this quantity, possibly
one-half is used as a 25 to 50 Brix cover syrup in packing
sections (21). Mixtures of sucrose and dextrose are used that
presently can be recovered from citrus waste liquors by methods
that may show economical advantage over the purchase of raw
sugar. Either citrus press liquor or juice from cull fruit can


58







By-Products of Florida Citrus


be processed into a suitable bland syrup, although considerable
technology is required. It is impractical, however, to expect to
recover crystallized sugars economically from waste citrus
liquors.
The refinement of citrus waste liquors into a bland syrup
requires the following operations: clarification, ion exchange,
purification, decolorization, and concentration. When citrus
press liquor is the source material, it is clarified by distilling
the peel oil from the liquor and allowing insolubles to settle, as
mentioned under the manufacture of citrus molasses. There is,
however, a preference by some to use two-stage centrifugation,
since in heating there is some chance of imparting more color
or setting the color so that it can not be removed by activated
carbon later. The clarified liquor is next passed through a cat-
ionic exchange bed at an approximate flow rate of 2 gallons
per minute per cubic foot of resin. If the liquor has been heated
during clarification, it must be cooled below 1200 F before en-
tering the exchanger. The highly acid effluent from the cationic
exchanger is passed subsequently through a granular carbon
bed to decolorize the solution and to remove the bitterness im-
parted by the glucosides. The demineralizing of the colorless
liquor is completed in an anion exchange bed, whereupon the
sweet dilute liquor is concentrated to 75 to 85 Brix in con-
ventional multiple-effect evaporators.
Citrus bland syrup has a tendency to darken in storage,
probably because of the incomplete removal of nitrogen com-
pounds. Somewhat similarly, care is needed in eliminating the
last traces of bitterness, because its taste is accentuated during
consumption. Trace bitterness can be avoided by passing the
dilute sweet liquor through another activated carbon bed just
prior to the concentration step.
A bland syrup for table consumption can be prepared from
tangerine juice, according to Atkins et al. (7). The final product
is light brown in color, 72 Brix, and has a distinctive flavor
suggesting honey and fruit. It is made by first treating tange-
rine juice with an excess of calcium carbonate. The pH is ad-
justed with citric acid, and the juice is partially concentrated
prior to treatment with activated carbon. After being filtered,
the processed tangerine juice is evaporated to 720 Brix. This
syrup also darkens in storage.
Sugar syrups that have been used to candy citrus peel often


59







Florida Agricultural Experiment Stations


are sold later as a table syrup. Candy manufacturers can also
consume this used syrup.

Peel Seasoning
A special market, more limited than the cattle feed one,
exists for carefully dehydrated citrus peel. It is sold as a special
ingredient for the later manufacture of medicines, liquors, con-
fectionery products, bakery goods, and seasoning.
Citrus peel for this purpose must be cleaned of membrane,
rag, and seeds. The peel from a Brown extractor is ideally
suited. It is washed, treated with anti-oxidants, and either
dried in tray driers or comminuted and dried in a commercial
drier. Great care is necessary with commercial rotary driers
to avoid burned particles that occur when there is sticking. The
essential oil content of a comminuted and dried peel is lower
than that produced by tray drying, and it is doubtful that it
would meet the minimum oil standards for some uses.
The dried product normally is bright in appearance and is
ground to pass completely a 12 mesh screen, but should have
at least 25 percent caught by a 40 mesh screen. Moisture should
be 4 to 5 percent by toluene extraction, and the product should
have at least 2-1/2 percent volatile oil. Bright color is stabilized
by low moisture content, while certain precautions are neces-
sary to preserve the oxidative stability of the volatile oil.


FERMENTATION PRODUCTS
The conversion of cull citrus and waste citrus liquors into
economical channels is competitive with all waste carbohydrate
liquors. It is frequently necessary, therefore, to re-evaluate
whether waste citrus liquors should be converted into citrus
molasses or to one of a number of fermentation products.

Vinegar
Vinegar made from orange, grapefruit, and tangerine juices
has been judged to be exceptionally good, to be superior to cider
vinegar, and to have an interesting and distinctive flavor, ac-
cording to McNary and Dougherty (83). Vinegar made from
orange peel press liquor, however, deserved individual considera-
tion by virtue of its more competitive cost and entirely different


60







Florida Agricultural Experiment Stations


are sold later as a table syrup. Candy manufacturers can also
consume this used syrup.

Peel Seasoning
A special market, more limited than the cattle feed one,
exists for carefully dehydrated citrus peel. It is sold as a special
ingredient for the later manufacture of medicines, liquors, con-
fectionery products, bakery goods, and seasoning.
Citrus peel for this purpose must be cleaned of membrane,
rag, and seeds. The peel from a Brown extractor is ideally
suited. It is washed, treated with anti-oxidants, and either
dried in tray driers or comminuted and dried in a commercial
drier. Great care is necessary with commercial rotary driers
to avoid burned particles that occur when there is sticking. The
essential oil content of a comminuted and dried peel is lower
than that produced by tray drying, and it is doubtful that it
would meet the minimum oil standards for some uses.
The dried product normally is bright in appearance and is
ground to pass completely a 12 mesh screen, but should have
at least 25 percent caught by a 40 mesh screen. Moisture should
be 4 to 5 percent by toluene extraction, and the product should
have at least 2-1/2 percent volatile oil. Bright color is stabilized
by low moisture content, while certain precautions are neces-
sary to preserve the oxidative stability of the volatile oil.


FERMENTATION PRODUCTS
The conversion of cull citrus and waste citrus liquors into
economical channels is competitive with all waste carbohydrate
liquors. It is frequently necessary, therefore, to re-evaluate
whether waste citrus liquors should be converted into citrus
molasses or to one of a number of fermentation products.

Vinegar
Vinegar made from orange, grapefruit, and tangerine juices
has been judged to be exceptionally good, to be superior to cider
vinegar, and to have an interesting and distinctive flavor, ac-
cording to McNary and Dougherty (83). Vinegar made from
orange peel press liquor, however, deserved individual considera-
tion by virtue of its more competitive cost and entirely different


60







Florida Agricultural Experiment Stations


are sold later as a table syrup. Candy manufacturers can also
consume this used syrup.

Peel Seasoning
A special market, more limited than the cattle feed one,
exists for carefully dehydrated citrus peel. It is sold as a special
ingredient for the later manufacture of medicines, liquors, con-
fectionery products, bakery goods, and seasoning.
Citrus peel for this purpose must be cleaned of membrane,
rag, and seeds. The peel from a Brown extractor is ideally
suited. It is washed, treated with anti-oxidants, and either
dried in tray driers or comminuted and dried in a commercial
drier. Great care is necessary with commercial rotary driers
to avoid burned particles that occur when there is sticking. The
essential oil content of a comminuted and dried peel is lower
than that produced by tray drying, and it is doubtful that it
would meet the minimum oil standards for some uses.
The dried product normally is bright in appearance and is
ground to pass completely a 12 mesh screen, but should have
at least 25 percent caught by a 40 mesh screen. Moisture should
be 4 to 5 percent by toluene extraction, and the product should
have at least 2-1/2 percent volatile oil. Bright color is stabilized
by low moisture content, while certain precautions are neces-
sary to preserve the oxidative stability of the volatile oil.


FERMENTATION PRODUCTS
The conversion of cull citrus and waste citrus liquors into
economical channels is competitive with all waste carbohydrate
liquors. It is frequently necessary, therefore, to re-evaluate
whether waste citrus liquors should be converted into citrus
molasses or to one of a number of fermentation products.

Vinegar
Vinegar made from orange, grapefruit, and tangerine juices
has been judged to be exceptionally good, to be superior to cider
vinegar, and to have an interesting and distinctive flavor, ac-
cording to McNary and Dougherty (83). Vinegar made from
orange peel press liquor, however, deserved individual considera-
tion by virtue of its more competitive cost and entirely different


60







By-Products of Florida Citrus


flavor. Its color was darker and aroma more fruity than that
made from citrus fruit juices.
Vinegar making is a two-step process in which the raw
material must first undergo an alcoholic fermentation with yeast.
Strain of yeast did not appreciably affect the quality of the
final vinegar, according to McNary et al. (83). The acetic acid
fermentation, second step of the process, was completed by three
procedures: 1, the slow or Orleans process; 2, the generator
process; and 3, submerged fermentation. Acetification efficiencies
of 95 percent were reported (83) for submerged-type fermen-
tation.
Peel oil was found to be responsible for objectionable off-
flavors in vinegar. Elimination of peel oil by filtration, clari-
fication, or distillation, prior to the alcohol fermentation, pro-
duced a satisfactory product. Filtration of citrus juices was not
satisfactory without addition of pectic enzymes. This led to a
new problem: the spent enzymes polymerized and formed a
sediment after lengthy storage. This sediment did not affect
the quality of the vinegar, but was objectionable because of
its unsightliness.
Vinegar production from citrus juices presents a further
problem in that the juices do not contain sufficient sugar to
yield 4 percent acetic acid without partial concentration or the
addition of sugar. The legality of sugar addition in this case
is not known.


Feed Yeast
Although citrus press liquor is normally concentrated to
citrus molasses, it also can be used advantageously in the pro-
duction of feed yeast. Yeast has considerable value as a feed
supplement, since it is one of the richest natural sources of the
B vitamins and contains about 50 percent protein. The possi-
bility of fermenting citrus press liquor to feed yeast and alcohol
was investigated by Nolte and co-workers (95). Torula utilis,
a wild, fast-growing yeast, was selected finally because it propa-
gated rapidly and produced little alcohol. Furthermore, this
organism appeared to give the best yeast yield of the five tested.
Since the press liquor contained insufficient nitrogen and phos-
phates for optimum growth of the fungus, it was necessary to
add nutrient salts. Yields of dry yeast by batch operation ranged


61







Florida Agricultural Experiment Stations


from 44 to 48 percent of the total sugar content of the press
liquor. Diluted press liquor, containing not more than 1 per-
cent total sugars, produced higher yeast yields and faster propa-
gation of the fungus.
Citrus liquors were adapted later to a continuous method
of fermentation by Veldhuis and Gordon (124). The method
was developed originally for the utilization and disposal of
liquors obtained during the manufacture of starch from sweet
potatoes. Yields of 60 percent were obtained when press liquor
was diluted with two volumes of water, while only 33 percent
yields were obtained with full strength press liquor. This is the
equivalent of 36 to 20 pounds of feed yeast per 1,000 pounds
of 10' Brix press liquor processed. The analysis of a 10-sample
composite of feed yeast from press liquor is shown in Table 12.
Significant quantities of thiamin, riboflavin, ergosterol, niacin,
and pantothenic acid were also present in the yeast.


Table 12.-Composition of Dry Yeast and Analysis of Ash (95).
Dry Yeast Percent Ash Percent
Moisture 1.29 Phosphorus pentoxide 45.75
Protein (N x 6.25) 55.28 Magnesium oxide 4.95
Crude fat 4.51 Calcium oxide 1.26
Glycogen 12.78 Silicon dioxide 2.58
Cellulose, gum, etc. 18.06 Sulfur trioxide 7.79
Ash 8.08 Chlorine 0.22
Iron oxide 0.40
Sodium and potassium
oxides 37.05



Citric and Lactic Acid
Citric acid is the most widely used organic acid for the acidi-
fication of foods. It is distributed widely in plants, and the most
abundant natural sources are citrus fruits such as lemons and
limes. Accordingly, it was recovered for years from lemon juice
although seldom, if ever, in Florida. Today, commercial pro-
duction of citric acid by submerged culture fermentation has
practically replaced all other methods (120). Strains of fungi


62







By-Products of Florida Citrus


belonging to Aspergillus niger are used most frequently, and
yields of about 60 percent are obtained from the sugar con-
sumed (44). Beet molasses is the more common substrate for
this fermentation.
Karow and Waksman (65) have shown that high concentra-
tions of nitrogen and phosphate in molasses can limit citric
acid yields. When production of citric acid was attempted from
citrus molasses by Gadem et al. (38) using A. niger, the mo-
lasses was found unsuitable until treated by ion exchange to
remove metal ions and supplemented with additional nitrogen,
phosphorus, and magnesium. Even after purification and sup-
plementation, only 35 percent yields of citric acid were obtained
from the sugar consumed over a period of four days.
Lactic acid is another of the many products that can be
profitably recovered at times from sugar-containing waste
liquors after fermentation. This fermentation has been carried
out by Nolte et al. (94) with grapefruit juice and suggested by
them for other citrus juices, citrus press liquor, and citrus
molasses. Although lactic acid bacteria of the Lactobacillus del-
brueckii type are usually used, Nolte et al. (94) obtained bet-
ter results with the lactobacilli normally present on the fruit.
It was found advantageous to prepare a starter culture that
was incubated two to three days at 122 F prior to use. The grape-
fruit juice to be fermented is neutralized with calcium carbonate
and warmed to 122 F. The starter is added, and during fermen-
tation the pH is maintained between 4.0 and 6.5. The fermen-
tation is inhibited by free lactic acid over 1.5 percent concen-
tration. Six to eight days are required to complete the fermen-
tation. Yields of lactic acid from the sugars of grapefruit juice
ranged from 71 to 84 percent. Sugar consumption varied from
76 to 94 percent in these trials. The lactic acid formed is re-
covered as the calcium salt by crystallization from the concen-
trated fermentation liquor. Purification is by recrystallization,
and the free acid is obtained by adding sulfuric acid.
Food-grade calcium lactate is used principally in the manu-
facture of special baking powders. Sodium lactate can be used
as a humectant in tobacco, while the free lactic acid is used to
adjust the pH in the production of beer, jellies, cheese, dried
egg whites, and other food products (61). The greatest poten-
tial market is expected to be the lactic acid derivatives, espe-
cially acrylic esters.


63







Florida Agricultural Experiment Stations


Butylene Glycol, 2-3
Conversion of citrus press liquor and diluted citrus molasses
to 2,3-butylene glycol was investigated by Long and Patrick
(80) as an alternative and potentially rewarding means of
utilizing citrus waste liquors. Many industrial uses for the
product exist, such as: softeners for textile sizing, solvents for
dyes, components of synthetic resins, carriers for pharmaceu-
tical products, and automotive antifreeze.
Favorable conditions for maximum glycol production by this
fermentation were as follows: citrus molasses or press liquor
was diluted or concentrated respectively by 20 Brix, tempera-
ture was maintained at 29 to 30' C, the pH was adjusted periodi-
cally to maintain 6.0 to 6.2, and mineral nutrients were always
added. The minerals added to the substrate were 0.2 percent
potassium diacid phosphate and 0.4 percent urea. Stirring and
aeration were necessary, but the rates were not critical. Prior
adaptation of the cultures to press liquor or diluted molasses
was responsible for more rapid completion of the fermentation
with only slight effect on total glycol production. Two Aerobacter
species, A. aerogenes strain NRRL B-199 and one designated
A-101, were investigated; the latter culture consistently gave
higher glycol yields and greater reduction in total sugars. Under
the most ideal conditions, there was a maximum glycol produc-
tion of 4.8 to 5.3 percent in 48 to 64 hours. Residual sugars,
however, varied from 1.4 to 3.1 percent.
The economical recovery of 2,3-butylene glycol from the
fermentation mash was the greatest problem and has been re-
viewed recently by Long and Patrick (81). Possible solutions
were: 1, distillation after addition of a suitable high-boiling
liquid; 2, solvent extraction; and 3, countercurrent steam strip-
ping.

Wines, Brandies, and Citrus Alcohol
Orange and grapefruit juice can be converted into wines of
pleasant taste and aroma, but require the addition of sugars
and carefully controlled conditions, according to von Loesecke
et al. (126). Wines made from juices of different varieties of
orange were not decidedly different, but were distinguishable
from those of grapefruit juice in aroma and taste. Citrus wines
do not possess an orange or grapefruit flavor, but more resemble


64







Florida Agricultural Experiment Stations


Butylene Glycol, 2-3
Conversion of citrus press liquor and diluted citrus molasses
to 2,3-butylene glycol was investigated by Long and Patrick
(80) as an alternative and potentially rewarding means of
utilizing citrus waste liquors. Many industrial uses for the
product exist, such as: softeners for textile sizing, solvents for
dyes, components of synthetic resins, carriers for pharmaceu-
tical products, and automotive antifreeze.
Favorable conditions for maximum glycol production by this
fermentation were as follows: citrus molasses or press liquor
was diluted or concentrated respectively by 20 Brix, tempera-
ture was maintained at 29 to 30' C, the pH was adjusted periodi-
cally to maintain 6.0 to 6.2, and mineral nutrients were always
added. The minerals added to the substrate were 0.2 percent
potassium diacid phosphate and 0.4 percent urea. Stirring and
aeration were necessary, but the rates were not critical. Prior
adaptation of the cultures to press liquor or diluted molasses
was responsible for more rapid completion of the fermentation
with only slight effect on total glycol production. Two Aerobacter
species, A. aerogenes strain NRRL B-199 and one designated
A-101, were investigated; the latter culture consistently gave
higher glycol yields and greater reduction in total sugars. Under
the most ideal conditions, there was a maximum glycol produc-
tion of 4.8 to 5.3 percent in 48 to 64 hours. Residual sugars,
however, varied from 1.4 to 3.1 percent.
The economical recovery of 2,3-butylene glycol from the
fermentation mash was the greatest problem and has been re-
viewed recently by Long and Patrick (81). Possible solutions
were: 1, distillation after addition of a suitable high-boiling
liquid; 2, solvent extraction; and 3, countercurrent steam strip-
ping.

Wines, Brandies, and Citrus Alcohol
Orange and grapefruit juice can be converted into wines of
pleasant taste and aroma, but require the addition of sugars
and carefully controlled conditions, according to von Loesecke
et al. (126). Wines made from juices of different varieties of
orange were not decidedly different, but were distinguishable
from those of grapefruit juice in aroma and taste. Citrus wines
do not possess an orange or grapefruit flavor, but more resemble


64







By-Products of Florida Citrus


a grape sauterne wine or can be modified to have a sherry-like
flavor and color. Citrus wines can be converted into vermouths
that are comparable in quality to imported types.
In manufacturing citrus wines, von Loesecke et al. (126)
found it important to ream the fruit carefully for juice because
excessive peel oil would inhibit the fermentation. The bitter-
ness of naringin in grapefruit juice, if excessive, was removed
with activated charcoal after fermentation. When six Sacchar-
omyces cultures of wine yeast were tried, the resulting wines
failed to show any marked difference in either bouquet or taste.
In most cases, sugar was added until the Brix was 24 (1.5 to
1.75 pounds per gallon), and care was taken during the fermen-
tation to maintain the temperature at about 60 F. Higher
temperatures caused lower alcohol content and darker color.
Approximately 10 or 11 days were required for completion of
the fermentation, after which the wine was syphoned, filtered,
and sweetened either to 3 or 5 percent sugar content. After
seven months' storage in plain or charred oak barrels at tempera-
tures between 80 and 90 F, the beverage was considered pala-
table.
Since citrus wines darken and develop a disagreeable odor
very readily, Cruess (24) has found it important to add and
maintain between 100 to 300 ppm of sulfur dioxide at all stages
in its production. He suggested pectinol enzyme as useful in
clearing the wine. It was sometimes important also that a
portion of the citric acid in the juice be neutralized with potas-
sium carbonate or calcium carbonate. The latter adds a dis-
agreeable musty flavor, according to von Loesecke et al. (126).
Orange and grapefruit spirits and brandy are obtained by
distilling the fermented orange and grapefruit juices (126).
Neither aroma nor taste suggests the fruit of origin. Grapefruit
and orange brandies that are aged in plain oak barrels, how-
ever, can be distinguished from each other.
When preparing citrus cordials, citrus spirits are used as a
base, and sugar syrup and peel oil are added. A better product
is obtained from citrus spirits than from ordinary molasses
alcohol (126).
For a number of years, citrus molasses has been used as a
sugar source for production of ethyl alcohol which can be
utilized as a brandy neutral spirits. Fig. 14 shows a plant for
this operation. In this fermentation, pure yeast cultures are


65







Florida Agricultural Experiment Stations


Fig. 14.-Fermenter tanks and housing for the alcohol rectifiers are shown.
(Picture taken at Florida Fruit Distillers, Inc., Lake Alfred.)


used, and the molasses is diluted to 15 to 20 Brix. Nolte et al.
(95) have found that citrus press juice is too dilute for economi-
cal recovery of alcohol. The fermentation is quite rapid, and
the alcohol is recovered in a continuous rectification process.
The concentrated alcohol from a beer still is refined in a recti-
fying column. The final product is used in the manufacture of
vodka, gin, and exotic mixtures.
The "distillery solubles" discharged from the bottom of the
beer still are free of alcohol and are sent to disposal pits or
used in pasture improvement programs. If the distillery solubles
Share concentrated, they may be used to stabilize vitamin A in
feed mixtures.

WASTE DISPOSAL
The citrus industry has eliminated the greater part of a
difficult disposal problem by utilizing the large quantities of
citrus residues in the production of by-products. There are,
however, the more dilute waste waters from the can-cooler, fruit
washers, peeling tables, sectioninzing tables, barometric legs,
floor clean-ups, and others that still represent a problem. The
seasonal and day to day variations in this waste load have com-


66







By-Products of Florida Citrus


plicated the problem, but even so, other by-products and progress
have resulted.
The substitution of condensed water from orange concen-
trate evaporators in place of well water in fulfilling the make-up
water requirements of a processors' boilers is an interesting
example of useful recovery of dilute waste water. Electronic
safeguards and prevention of entrainment are necessary in this
application.


Methods of Disposal
Some of the methods for disposing of dilute wastes that have
been used with only limited success are: 1, emptying into lakes;
2, handling by city sewerage system; 3, primary settling beds;
and 4, flooding of waste lands. Dilute waste effluent from citrus
canneries has a five-day biological oxygen demand (B.O.D.)
varying from 100 to 2,000 ppm, according to von Loesecke et al.
(125). Purification of the waste effluents by chemical precipita-
tion, activated sludge, contact filter, sand filter, and trickling
filter were some of the procedures investigated. The latter
offered the most promising solution, but costs were estimated
to be high.
Trickling filters operated either in series or at high recircula-
tion ratios were reported by Wakefield (127) to offer a practi-
cal means of treating citrus processing liquid waste. The addi-
tion of 50 ppm nitrogen and 20 ppm phosphorus gave the
highest and most uniform filter performance. High rate trick-
ling filters were capable of removing organic matter requiring
an average of 0.182 pounds of stabilizing oxygen (B.O.D.) per
cubic foot of filter volume.
The alkaline waste liquor from the grapefruit peeling opera-
tion in canneries was particularly disruptive to liquid waste
treating processes. However, Kilburn (75) has shown that this
liquor can be substituted advantageously in citrus pulp and
molasses manufacture.


Biological Treatment
A methane fermentation appeared to be suitable as a treat-
ment for citrus waste water, but McNary et al. (85) found that
a natural yeast fermentation and aeration had to precede it.


67







By-Products of Florida Citrus


plicated the problem, but even so, other by-products and progress
have resulted.
The substitution of condensed water from orange concen-
trate evaporators in place of well water in fulfilling the make-up
water requirements of a processors' boilers is an interesting
example of useful recovery of dilute waste water. Electronic
safeguards and prevention of entrainment are necessary in this
application.


Methods of Disposal
Some of the methods for disposing of dilute wastes that have
been used with only limited success are: 1, emptying into lakes;
2, handling by city sewerage system; 3, primary settling beds;
and 4, flooding of waste lands. Dilute waste effluent from citrus
canneries has a five-day biological oxygen demand (B.O.D.)
varying from 100 to 2,000 ppm, according to von Loesecke et al.
(125). Purification of the waste effluents by chemical precipita-
tion, activated sludge, contact filter, sand filter, and trickling
filter were some of the procedures investigated. The latter
offered the most promising solution, but costs were estimated
to be high.
Trickling filters operated either in series or at high recircula-
tion ratios were reported by Wakefield (127) to offer a practi-
cal means of treating citrus processing liquid waste. The addi-
tion of 50 ppm nitrogen and 20 ppm phosphorus gave the
highest and most uniform filter performance. High rate trick-
ling filters were capable of removing organic matter requiring
an average of 0.182 pounds of stabilizing oxygen (B.O.D.) per
cubic foot of filter volume.
The alkaline waste liquor from the grapefruit peeling opera-
tion in canneries was particularly disruptive to liquid waste
treating processes. However, Kilburn (75) has shown that this
liquor can be substituted advantageously in citrus pulp and
molasses manufacture.


Biological Treatment
A methane fermentation appeared to be suitable as a treat-
ment for citrus waste water, but McNary et al. (85) found that
a natural yeast fermentation and aeration had to precede it.


67







Florida Agricultural Experiment Stations


This was necessary in order to eliminate citrus essential oils
which were toxic to the methane bacteria. Typical loading was
0.22 pounds dry solids of waste liquid per cubic foot of liquid
capacity per day. The daily volume of gas produced was 7 times
the liquid volume of the methane fermenter. Over-all reduction
in dry solids with the two-stage operation was 91.4 percent.
Approximately equal reduction in dry solids occurred during the
aerobic yeast fermentation as in the anaerobic stage. The
process was suited to the more dilute waste waters, or to those
that first have been pretreated.
An activated sludge process was demonstrated later by
Dougherty et al. (30) to be suited to the treatment of citrus
waste waters. Diluted orange juice was used initially on small
scale, but the procedure was tested later in a pilot plant adjacent
to a processing installation (84). B.O.D. was reduced by 99
percent or more in this procedure, as was shown in the labora-
tory investigation (30). The strength fluctuations in waste
liquor were very detrimental, and it was demonstrated that an
extreme overload was pernicious, but not fatal, to the sludge
culture. Under unfavorable conditions, slime-forming organisms,
Sphaerotilus, became prolific, but under favorable conditions
they decreased to unimportant numbers. A large population of
protozoa, including many Vorticella, indicated an active sludge
in good condition.
Optimum B.O.D. loading for safe operation and good sludge
production was found in a later investigation (28) to be 115
to 135 pounds per 1,000 cubic feet of aeration. The best level
of inorganic nutrients was 10 mg each of nitrogen and phosphate
per liter. Approximately 20 percent of the total solids in the
untreated waste was recovered as dry excess sludge.
The dry excess sludge from the treatment of citrus waste
waters by the activated sludge process was shown by Dougherty
and McNary (29) to contain 28.9 to 43.8 percent protein, to
have significant quantities of the B group vitamins, and to be a
particularly good source of B12. The B12 production was aug-
mented by small additions of cobalt, while the protein and
vitamin content were improved by nutrient additions of nitrogen
and phosphate.
Dried sludge could become, therefore, another of the many
useful by-products from citrus waste residues.


68







By-Products of Florida Citrus


ACKNOWLEDGMENTS
Acknowledgments are made to the following commercial
processors and manufacturers in Florida, whose earnest coopera-
tion contributed much to the success of this work: Kraft Foods
Division, Lakeland; Florida Citrus Canners Cooperative, Lake
Wales; Treesweet Products Company, Fort Pierce; Tropicana
Products, Inc., Bradenton and Cocoa; Pasco Packing Company,
Dade City; Plymouth Citrus Products Cooperative, Plymouth;
Suni-Citrus Products Company, Haines City; Southern Fruit
Distributors, Orlando; Winter Garden Citrus Products Coopera-
tive, Winter Garden; B & W Canning Company, Groveland;
Minute Maid Corporation, Orlando; Desoto Canning Company,
Arcadia.
Appreciation is expressed also to Adams Packing Association,
Inc., Auburndale; Libby, McNeil & Libby, Ocala; Salada Foods,
Inc., Plant City; H. P. Hood & Sons, Dunedin; Evans Packing
Company, Dade City; Hi-Acres Concentrate, Inc., Orlando;
Snively Groves, Inc., Winter Haven; Ben Hill Griffin, Inc., Frost-
proof; Golden Gem Growers, Inc., Umatilla; Universal Food
Products, Inc., Lakeland; Kuder Citrus Feed Company, Lake
Alfred, and Imperial Citrus By-Products Company, Lakeland.


69








70


Florida Agricultural Experiment Stations


LITERATURE CITED

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Florida. Fla. Dept. Agr. Bull. 2: 5-17. 1960.








By-Products of Florida Citrus 71

21. Carter, R. D. Effect of raw fruit Brix on canned grapefruit. Citrus
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22. Chapman, H. L., Jr., R. W. Kidder, and S. W. Plank. Comparative
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26. Davis, R. N., and A. R. Kemmerer. Lactating factors for dairy cows
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vitamin content and animal feed potential. Sewage Ind. Wastes. 30:
1151-5. 1958.

30. Dougherty, M. H., R. W. Wolford, and R. R. McNary. Treatment of
citrus waste water by activated sludge. Sewage Ind. Wastes 27:
821-6. 1955.
31. Driggers, J. C., G. K. Davis, and N. R. Mehrhof. Toxic factor in
citrus seed meal. Fla. Agr. Exp. Sta. Tech. Bull. 476: 5-36. 1951.

32. Eckey, E. W. Vegetable fats and oils. 836 pp. Reinhold Publishing
Corp. 1954.
33. Federal Register. Food additives Food additives permitted in ani-
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34. Florida Department of Agriculture. Florida Agricultural Statistics
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35. Florida Division of Fruit and Vegetable Inspection. Annual report -
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36. Freedman, L., and A. J. Merritt. Citrus flavonoid complex: chemical
fractionation and biological activity. Science 139: 344. 1963.
37. Gaddum, L. W. The pectic constituents of citrus fruits. Fla. Agr.
Exp. Sta. Tech. Bull. 268: 3-23. 1934.
38. Gadem, E. L., D. N. Petsiaras, and J. Winoker. Citrus waste utiliza-
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39. Glasscock, R. S., T. J. Cunha, A. M. Pearson, J. E. Pace, and D. M.
Buschman. Preliminary observations on citrus seed meal as a protein
supplement for fattening steers and swine. Fla. Agr. Exp. Sta. Circ.
S-12. 1950.








72 Florida Agricultural Experiment Stations

40. Goren, R. Thesis on physiological functions of hesperidin. Hebrew
Univ. of Jerusalem. 1963.
41. Guenther, E. The production of oil of limes. Amer. Perf. Ess. Oil.
Rev. Nov. and Dec. 1942 and Jan., Feb., March and April 1943.
Reprint 19 pp. 1943.
42. Hart, B. F. Flavanone compounds and preparation thereof. U. S.
Patent No. 2,926,162. February 23, 1960.
43. Held, J. L. Drying citrus cannery wastes and disposing of effluents.
Food Ind. 17: 1479-83. 1945.
44. Heid, J. L., and M. A. Joslyn. Food Processing Operations. Vol. II,
594 pp. Avi Publishing Co., Inc. 1963.
45. Hendrickson, R., and J. W. Kesterson. Citrus molasses. Fla. Agr.
Exp. Sta. Bull. 677: 3-27. 1964.
46. .-- -----.- ---..-- -- .--- Chemical analysis of citrus
bioflavonoids. Proc. Fla. State Hort. Soc. 70: 196-203. 1957.
47. .-- .....------------- ----- ---.. Florida lemon seed oil. Proc.
Fla. State Hort. Soc. 76: 249-53. 1963.
48. ------- -...-- ..--------...-.-..-- .... Glucoside azo dyestuffs. U. S.
Patent No. 2,748,107. May 29, 1956.
49. _...---.---.---... ------ .-.--. .- Grapefruit seed oil. Proc. Fla.
State Hort. Soc. 74: 219-23. 1961.
50. ..... ------ --.---- ---------- -....- Hesperidin in orange juice and
peel extracts determined by UV absorption. Proc. Fla. State Hort.
Soc. 72: 258-63. 1959.
51. .._.---------.._ _____ ....-----.. Hesperidin in Florida oranges.
Fla. Agr. Exp. Sta. Tech. Bull. 684: 3-42. 1964.
52. ---.--.- ----------.. --------.-----. Purification of crude hesperi-
din. Proc. Fla. State Hort. Soc. 68: 121-4. 1955.
53. .---- ----.-__ ..---. -.....----.-- .. Purification of naringin. Proc.
Fla. State Hort. Soc. 69: 149-52. 1956.
54. _----.... ----------------... Seed oils from Citrus sinensis.
J. Amer. Oil Chem. Soc. 40: 746-7. 1963.
55. -. ------... ._ ..--- -- __..-_. __.--- Storage changes in citrus mo-
lasses. Proc. Fla. State Hort. Soc. 63: 154-62. 1950.
56. ---. ... __---__ ...--------..-....- Viscosity of citrus molasses.
Proc. Fla. State Hort. Soc. 65: 226-8. 1952.
57. Higby, R. H. Method for recovery of flavanone glucosides. U. S.
Patent No. 2,421,061. May 27, 1947.
58. .- ----.........--...... .------..-- Method of manufacturing hes-
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59. -.------------.........--------------..---. Process for the manufacture of
hesperidin. U. S. Patent No. 2,348,215. May 9, 1944.
60. Horowitz, R. M. The citrus flavonoids. In: The orange, its biochemis-
try and physiology. Edited by W. B. Sinclair. 475 pp. Univ. of
Calif. Press. 1961.








By-Products of Florida Citrus 73

61. Inskeep, G. C., G. G. Taylor, and W. C. Breitzke. Lactic acid from
corn sugar. Ind. Eng. Chem. 44: 1955-66. 1955.
62. Iranzo, J. R., and M. K. Veldhuis. The composition of Florida citrus
molasses. Proc. Fla. State Hort. Soc. 61: 205-11. 1948.

63. Jamieson, G. S. Vegetable fats and oils. 508 pp. Reinhold Publishing
Corp. 1943.
64. Jones, R. W., M. G. Stout, H. Reich, and M. N. Huffman. Cytostatic
activities of certain flavonoids against zebra-fish embryos. Cancer
Chemother. Rep. 34: 5-6. 1964.
65. Karow, E. 0., and S. A. Waksman. Production of citric acid in sub-
merged culture. Ind. Eng. Chem. 39: 821-5. 1947.
66. Kertesz, Z. I. The pectic substances. 628 pp. Interscience Publishers,
Inc. 1951.
67. Kesterson, J. W. A discussion of the methods for the production of
essential oils in Florida. Transactions of the 1961 Citrus Engineering
Conference Fla. Section A.S.M.E.-Lakeland, Florida, March 22,
1961.
68. Kesterson, J. W., and R. Hendrickson. A comparison of red and white
grapefruit oils. Amer. Perf. and Cosmetics 79: 1: 34-6. 1964.
69. -- ------------- ..---- ____--...- A comparison of two commer-
cial methods for the production of citrus oils in Florida. Amer. Perf.
and Aromatics 67: 2: 35-8. 1956.
70. --------- ------------ .. ... _-- Essential oils from Florida
citrus. Fla. Agr. Exp. Sta. Bull. 521: 5-70. 1953.

71. .- ... ..... ..---- ------- -. .... .. E valuation of coldpressed
Marsh grapefruit oil. Amer. Perf. and Cosmetics 78: 5: 32-5. 1963.
72. --.-... Naringin, a bitter principle of
grapefruit. Fla. Exp. Sta. Tech. Bull. 511: 5-35. 1953.
73. ------------- ........... The composition of Valencia
orange oil as related to fruit maturity. Amer. Perf. and Cosmetics
77: 12: 21-4. 1962.
74. Kesterson, J. W., R. Hendrickson, and G. J. Edwards. Coldpressed
orange oil-physicochemical procedure to determine origin and method
of extraction. Amer. Perf. and Aromatics 74: 4: 33-4 and 52. 1959.
75. Kilburn, R. W. Reduction of scale formation in citrus molasses evapo-
rators. Proc. Fla. State Hort. Soc. 65: 253-5. 1952.

76. Kirk, W. G., E. M. Kelly, H. J. Fulford, and H. E. Henderson. Feed-
ing value of citrus and blackstrap molasses for fattening cattle. Fla.
Agr. Exp. Sta. Bull. 575: 3-23. 1956.
77. Kirk, W. G., E. R. Felton, H. J. Fulford, and E. M. Hodges. Citrus
products for fattening cattle. Fla. Agr. Exp. Sta. Bull. 454: 5-16.
1949.
78. Kirk, W. G., and G. K. Davis. Citrus products for beef cattle. Fla.
Agr. Exp. Sta. Bull. 538: 5-16. 1954.
79. Laudans, H., and D. F. Davis. Dried citrus pulp insect problem and
its possible solution with insecticides coated paper bags. Proc.
Fla. State Hort. Soc. 69: 191-5. 1956.








74 Florida Agricultural Experiment Stations

80. Long, S. K., and R. Patrick. Production of 2,3-butylene glycol from
citrus wastes. App. Microbiology 9: 244-8. 1961.

81. .- .-. .... The present status of the 2,3-butylene
glycol fermentation. Adv. App. Microbiology 5: 135-55. 1963.
82. Lorenz, A. J., and L. J. Arnold. Preparation and estimation of crude
citrin solutions from lemons. Food Research 6: 151-6. 1941.
83. McNary, R. R., and M. H. Dougherty. Citrus vinegar. Fla. Agr. Exp.
Sta. Bull. 622: 3-23. 1960.

84. McNary, R. R., R. W. Wolford, and M. H. Dougherty. Pilot plant
treatment of citrus waste water by activated sludge. Sewage Ind.
Wastes 28: 894-905. 1956.

85. McNary, R. R., R. W. Wolford, and V. D. Patton. Experimental
treatment of citrus waste water. Food Tech. 5: 319-23. 1951.
86. Miller, R. L. The place of citrus by-products in the feed industry.
Citrus Ind. 30: 3: 16-7. 1949.
87. Morrison, F. B. Feeds and feeding. 21st Ed. 1207 pp. The Morrison
Publishing Co. 1949.
88. Neal, W. M., R. B. Becker, and P. T. Dix Arnold. The feeding value
and nutritive properties of citrus by-products. I. The digestible
nutrients of dried grapefruit and orange refuse, and the feeding value
of the grapefruit refuse for growing heifers. Fla. Agr. Exp. Sta.
Bull. 275: 3-26. 1935.
89. Newhall, W. F. Derivatives of (+)-limonene. I. Esters of trans-p-
methane-1,2-diol. J. Org. Chem. 23: 1274-6. 1958.
90. -----.. ---..- .- ... ... Derivatives of (+)-limonene.
II. 2-amino-l-p-menthanols. J. Org. Chem. 24: 1673-6. 1959.
91. .---.--. .......... ..._.... Derivatives (+) limonene.
III. A stereospecific synthesis of cis- and trans-p-menthene 1,2-epox-
ides. J. Org. Chem. 29: 185-7. 1964.

92. Newhall, W. F., and J. W. Kesterson. Factors affecting the autoxida-
tion of d-limonene during storage. Proc. Fla. State Hort. Soc. 74:
239-43. 1961.
93. Nolte, A. J., and H. W. von Loesecke. Grapefruit seed oil, manufac-
ture and physical properties. Ind. Eng. Chem. 32: 1244-6. 1940.
94. -. ------.-------- -.. ----.. ----.. ..- Possibilities of preparing lac-
tic acid from grapefruit juice. Fruit Prod. J. 19: 204-5, 216, 220. 1940.
95. Nolte, A. J., H. W. von Loesecke, and G. N. Pulley. Feed yeast and
industrial alcohol from citrus waste press juice. Ind. Eng. Chem.
34: 670-3. 1942.
96. Ohta, M. Derivatives of hesperidin and process for preparing the
same. U. S. Patent No. 2,350,804. June 6, 1944.
97. Patrick, R., and W. F. Newhall. Fungicidal activity of some new
amino alcohols synthesized from citrus (+)-limonene. Agr. Food
Chem. 8: 397-9. 1960.
98. Peacock, F. M., and W. G. Kirk. Comparative feeding value of dried
citrus pulp, corn feed meal, and ground snapped corn for fattening
steers in drylot. Fla. Agr. Exp. Sta. Bull. 616: 3-12. 1959.







By-Products of Florida Citrus 75

99. Poore, H. D. Recovery of naringin and pectin from grapefruit
residue. Ind. Eng. Chem. 26: 637-9. 1934.
100. Pritchett, D. E., and H. E. Merchant. The purification of hesperidin
with formamide. J. Amer. Chem. Soc. 68: 2108. 1946.
101. Pulley, G. N., and H. W. von Loesecke. Drying method changes com-
position of grapefruit by-product. Food Ind. 12: 6: 62-3, 100-1. 1940.
102. .. ... .... .....------- Preparation of rhamnose from
naringin. J. Amer. Chem. Soc. 61: 175-6. 1939.
103. Pulley, G. N., E. L. Moore, and C. D. Atkins. Grapefruit cannery
waste yields crude citrus pectin. Food Ind. 16: 4: 94-6, 136-7. 1944.
104. Rouse, A. H. Distribution of pectinesterase and total pectin in com-
ponent parts of citrus fruits. Food Tech. 7: 360-2. 1953.
105. Rouse, A. H., and C. D. Atkins. Pregelation in bitter orange marma-
lade bases. Proc. Fla. State Hort. Soc. 70: 223-8. 1957.
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