Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 243
Title: Type, variety, maturity and physiological anatomy of citrus fruits as affecting quality of prepared citrus juices
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Permanent Link: http://ufdc.ufl.edu/UF00026418/00001
 Material Information
Title: Type, variety, maturity and physiological anatomy of citrus fruits as affecting quality of prepared citrus juices
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 56 p. : ill. ; 23 cm.
Language: English
Creator: Camp, A. F ( Arthur Forrest ), 1896-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1932
 Subjects
Subject: Citrus juices   ( lcsh )
Citrus fruits -- Quality   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 54-56.
Statement of Responsibility: by A.F. Camp ... <et al.>.
General Note: Cover title.
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Bibliographic ID: UF00026418
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924097
oclc - 18204563
notis - AEN4701

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HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida




MR. F. H. HULL,


Bulletin 243 May, 1932


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director






TYPE, VARIETY, MATURITY AND

PHYSIOLOGICAL ANATOMY

OF CITRUS FRUITS

AS AFFECTING QUALITY OF

PREPARED CITRUS JUICES


By

A. F. CAMP, Horticulturist, Florida Experiment Station;
HAMILTON P. TRAUB, Horticulturist, Division of Horticultural
Crops and Diseases, Bureau of Plant
Industry, 17. S. Department of Agricul-
ture;
LEONARD W. GADDUM, Biochemist, Florida Experiment Station;
ARTHUR L. STAHL, Assistant Horticulturist, Florida Experiment
Station.






Bulletins will be sent free upon application to the
Agricultural Experiment Station
GAINESVILLE, FLORIDA










EXECUTIVE STAFF

John J. Tigert, M.A., LL.D., President of the
University
Wilmon Newell, D.Sc., Director
H. Harold Hume, M.S., Asst. Dir., Research
Sam T. Fleming, M.A., Asst.Dir.,Administration
J. Francis Cooper, M.S.A., Editor
R. M. Fulghum, B.S.A., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Secretary
K. H. Graham, Business Manager
Rachel McQuarrie, Accountant

MAIN STATION, GAINESVILLE
AGRONOMY
W. E. Stokes, M.S., Agronomist
W. A. Leukel, Ph.D., Associate
G. E. Ritchey, M.S.A., Assistant*
Fred H, Hull, M.S., Assistant
J. D. Warner, M.S., Assistant
John P. Camp, M.S., Assistant

ANIMAL HUSBANDRY
A. L. Shealy, D.V.M., Veterinarian in Charge
E. F. Thomas, D.V.M., Assistant Veterinarian
W. W. Henley, B.S.A., Assistant Veterinarian
R. B. Becker, Ph.D., Associate in Dairy In-
vestigations
W. M. Neal, Ph.D., Asst. in Animal Nutrition
P. T. Dix Arnold, B.S.A., Assistant in Dairy
Investigations
CHEMISTRY
R. W. Ruprecht, Ph.D., Chemist
R. M. Barnette, Ph.D., Associate
C. E. Bell, M.S.. Assistant
J. M. Coleman, B.S., Assistant
H. W. Winsor, B.S.A., Assistant
H. W. Jones. M.S., Assistant
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural Economist
Bruce McKinley, A.B., B.S.A., Associate
M. A. Brooker, Ph.D., Associate
Zach Savage, M.S.A., Assistant
ECONOMICS, HOME
Ouida Davis Abbott, Ph.D., Head
L. W. Gaddum, Ph.D., Biochemist
C. F. Ahmann, Ph.D., Physiologist
ENTOMOLOGY
J. R. Watson, A.M., Entomologist
A. N. Tissot, Ph.D., Assistant
H. E. Bratley, M.S.A., Assistant
E. F. Grossman, M.A., Asso., Cotton Insects
P. W. Calhoun, Assistant, Cotton Insects
HORTICULTURE
A. F. Camp, Ph.D., Horticulturist
Harold Mowry, B.S.A., Associate
M. R. Ensign. M.S., Associate
A. L. Stahl, Ph.D., Assistant
G. H. Blackmon, M.S.A., Pecan Culturist
C. B. Van Cleef, M.S.A., Greenhouse Foreman
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist
George F. Weber, Ph.D., Associate
R. K. Voorhees, M.S., Assistant
Erdman West, M.S., Mycologist

*In cooperation with U.S.D.A.


BOARD OF CONTROL

P. K. Yonge, Chairman, Pensacola
A. H. Blanding, Bartow
Raymer F. Maguire, Orlando
Frank J. Wideman, West Palm Beach
Geo. H. Baldwin, Jacksonville
J. T. Diamond, Secretary, Tallahassee


BRANCH STATIONS

NORTH FLORIDA STATION, QUINCY
L. O. Gratz, Ph.D., Associate Plant Pathologist
in Charge
R. R. Kincaid, M.S., Asst. Plant Pathologist
W. A. Carver, Ph.D., Asso. Cotton Specialist
R. M. Crown, B.S.A., Asst. Agronomist, Cotton
Jesse Reeves, Farm Superintendent

CITRUS STATION. LAKE ALFRED
John H. Jefferies, Superintendent
Geo. D. Ruehle, Ph.D., Asst. Plant Pathologist
W. A. Kuntz, A.M., Asst. Plant Pathologist
B. R. Fudge, Ph.D., Assistant Chemist
W. L. Thompson, B.S., Assistant Entomologist

EVERGLADES STATION, BELLE GLADE
R. V. Allison, Ph.D., Soils Specialist in Charge
R. W. Kidder, B.S., Farm Foreman
R. N. Lobdell, M.S., Associate Entomologist
F. D. Stevens, B.S., Sugarcane Agronomist
H. H. Wedgeworth, M.S., Asso. Plant Path.
B. A. Bourne, M.S., Asso. Sugarcane Physi-
ologist
J. R. Neller, Ph.D., Associate Biochemist
A. Daane, Ph.D., Associate Agronomist
M. R. Bedsole, M.S.A., Assistant Chemist

SUB-TROPICAL STATION, HOMESTEAD
H. S. Wolfe,Ph.D.,Asso. Horticulturist in Chg.
Stacy O. Hawkins, M. A., Assistant Plant
Pathologist


FIELD STATIONS
Leesburg
M. N. Walker, Ph.D., Asso. Plant Pathologist
W. B. Shippy, Ph.D., Asst. Plant Pathologist
K. W. Loucks, M.S., Asst. Plant Pathologist
C. C. Goff, M.S., Assistant Entomologist
J. W. Wilson, Ph.D., Assistant Entomologist
Plant City
A. N. Brooks, Ph.D., Asso. Plant Pathologist
R. E. Nolen, M.S.A., Lab. Asst. in Plant Path.
Cocoa
A. S. Rhoads, Ph.D., Asso. Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Asso. Plant Pathologist
West Palm Beach
D. A. Sanders, D.V.M., Associate Veterinarian
Monticello
Fred W. Walker, Assistant Entomologist
Bradenton
David G. Kelbert, Asst. Plant Pathologist













TABLE OF CONTENTS

INTRODUCTION ........................... .... ........................................ ..................... 5
Acknowledgments ................... ...... ....................... ..................... 5
General statement of problem..........................--------------- 5
PLAN OF EXPERIMENT ....................... ...--..------. -------------- 6
MATERIALS AND METHODS........................--------------------------------- 8
Type, variety, and source of fruit................................ ....... ............ 8
Maturity of fruit ..------......................... ------- ------------------- 9
Methods of juice extraction.................................................... 9
"Handling" the juice -- -.......................--------- ------------ 10
Containers ..................--..--------------------------- 11
Methods of freezing, storage, and defrosting........................................... 11
Sanitation .....-...............-------------------------- 11
Analytical methods ................-..... --.-- .--------- --.--.. 11
PRESENTATION OF DATA...................-.........--------......-..------ 12
Changes in taste---............-------------------------------- 15
Tasting technique .......----..........-- .. ---- ------------ 15
Bitter taste ................------------.........------- 15
Localization and identification of bitter taste.............................. 16
Effect of type, variety, quality and maturity factors on de-
velopment of bitter taste......................... ................... .. 28
Effect of after treatment on development of bitter taste......... 30
Other taste qualities ................... .......................... 31
Changes in color .----......-.............-----------.------- 32
Nature of juice sac plastid pigments------................................ 34
Color changes due to citrus oil and other compounds................ 34
Changes in direction and rate of movement of suspended particles 42
SUM MARY .............................................................. 52
LITERATURE CITED .....- -.- ........---....--- 54











TYPE, VARIETY, MATURITY AND PHYSIOLOGICAL
ANATOMY OF CITRUS FRUITS
AS AFFECTING QUALITY OF PREPARED
CITRUS JUICES

By A. F. CAMP, HAMILTON P. TRAUB, LEONARD W. GADDUM
and A. L. STAHL
With the adaptation of the frozen-pack method to the preser-
vation of citrus juices during the past several years, the older
methods of bottling and sterilizing the juice after sedimentation
and clarification (12, 11, 6, 4) or carbonating the product (15)
are being superseded by methods which may make it possible to
market an article which is more nearly like the original juice.
As is true with any new development in industry, there are many
problems which need to be solved from a fundamental view-
point. Such problems include not only the effect of the physio-
logical anatomy of the fruit but also the effect of citrus type,
variety, quality and maturity. The methods of preparation,
packaging and storing the product also are of importance.
In connection with the quality of the product, it is of first
importance to know the causes responsible for the development
of undesirable tastes in the prepared juices on aging. It is of
value also to investigate the possibilities of securing a product
of excellent color, and which is not subject to rapid change due
to settling of the suspended particles.
The object of the manufacturer is obviously to put out a pro-

Acknowledgments:-Part of the work reported in this publication was
carried out independently by the Florida Experiment Station prior to
September 1, 1931, and a part of the work was conducted cooperatively
between the Florida Experiment Station and the Bureau of Plant Industry,
United States Department of Agriculture, beginning September 1, 1931.
Prior to this date, the following facilities had been assembled by the Flor-
ida Experiment Station: Cold storage and freezing apparatus; three types
of presses for the preparation of juices; vacuumizing equipment and cap-
ping machinery. Since this time, work has been carried on by the cooper-
ators primarily on the basis of division of labor-A. F. Camp had charge
of the facilities enumerated above and the preparation of juices by the
various methods; H. P. Traub, A. F. Camp, L. W. Gaddum and A. L. Stahl
planned and carried out the theoretical experiments in the research labora-
tories. Thanks are due to Mr. B. A. Merrill, Pensacola, Mr. Charles O.
Reiff, Marianna Fruit Company, and the Glen St. Mary Nurseries Com-
pany, for their whole-hearted cooperation in furnishing Satsuma fruits,
and to Mr. H. P. Byrum, Homestead, for furnishing limes.





Florida Agricultural Experiment Station


duct which is as nearly like the freshly prepared juice as it is pos-
sible to secure in order to serve either of two needs: (a) unfrozen,
cool-stored juices which are to be marketed locally within 36
hours after preparation, and (b) juices which are to be stored in
the frozen condition for a period up to eight months or longer, if
necessary, before marketing.
The preliminary data herein reported are presented at this
time because of their immediate value to those engaged in the
commercial preparation of citrus juices. No attempt is made
to present an exhaustive report and in most instances com-
plete reports of work on special phases of the problem will be
published separately as soon as they are completed.

PLAN OF EXPERIMENT
The causes of any undesirable changes in prepared citrus
juices from the time of preparation until delivery to the con-
sumer may be classified under two heads: (a) Those present in
the external environment, such as gases (particularly oxygen),
containers, temperature and methods of storage; (b) those hav-
ing their origin in the prepared juice itself as a result of the
amounts and character of solutes and extractives released by
the method of manufacture. Such factors could operate inde-
pendently or in combination.
In any consideration of the second set of causes a knowledge
of the structure and composition of the citrus fruit is of primary
importance. The citrus fruits as described by Fawcett and Lee
(14) "have a rind or peel, which serves as a cover to the pulp
or juicy part of the fruit. Viewing the parts more in detail, the
rind is made up of a cuticle on the outside, thinly covering an
epidermal layer of cells containing numerous oil vesicles. Ac-
cording to Tschirch and Oesterle (1895), the epidermal cells
and sub-epidermal cells contain numerous chromatophores, green
in young fruits and yellow in mature fruits; these chromato-
phores give the color to the fruits. A white spongy portion of
parenchymatous cells (albedo) lies within the epidermis next
to the pulp. The cells of this spongy layer are loosely arranged
toward the inner portions; in this cell layer are also found many
pockets containing oxalate crystals. Radially branching vascu-
lar bundles extend through this whole tissue of the fruit wall,
especially the outer layer. The inner flesh of the fruit consists
of compartments or segments, the walls of which are of thin






Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 7

tissues of epidermal origin. From these walls small hair-like
papillae emerge, which become club-shaped and later turgid and
closely compacted together and constitute the juice-containing
vesicles of the ripe fruit. There are also yellow chromatophores
of crystalline character in these vesicles. There is in fruit
usually a central axis composed of spongy tissue. As in leaves,
there is a ramifying system of veins and veinlets through the
segment walls to all parts of the fruit, containing the elements
analogous to the cells of the cambium and conducting vessels
of the wood and bark and connected therewith through the stem
to the roots." (See Fig. 1.)


Inner peel and veins

Juice saos


Central axis

Seed


Looular wall


Outer peel



Fig. 1.-Cross sectional view of Parson Brown orange showing tissues.

In addition to the tissues mentioned by these authorities, the
seeds should be included. They are attached by means of pla-
centae to the locular walls (segment walls) where these come
in contact with the central axis of the fruit. It is also of in-
terest to indicate that, among the constituents of certain of the
tissues, various glucosides occur (17, 21, 18, 44) and it has been
shown (44) that the glucoside content decreases with maturity.
Pectic substances also are known to occur in citrus fruits.
*Figures in parentheses (Italic) refer to Literature Cited in the back
of this bulletin.






8 Flol ihdt Agricultural Experiment Station-

Throughout its development the citrus fruit is continually
changing in composition; as a consequence, the extracted juice
\aries from sample to sample. In the whole fruit the juice is
contained within the juice sacs, or vesicles, and does not come
in contact with the various tissues that go to make up the re-
mainder of the fruit structure. In processes of juice.extraction,
however, the various tissues are broken, and the juice is mixed
with them; moreover, the extracted juice contains more or less
macerated material from these tissues in the form of solid par-
ticles and can take up from these particles any undesirable pro-
ducts that they may contain.
Citrus juice extracted by the usual methods is a buffered
solution with an effective acidity, according to certain reported
experiments, ranging from pH 2.1 to pH 4.3. The more ap-
parent solutes are total acids, 0.25 to 11 per cent; total sugars,
1.5 to 16 per cent; protein, 0.40 to 1.00 per cent, and total
ash, 0.20 to 0.40 per cent (35, 34, 5, .5. 9. 30, 29). In addition
there are undoubtedly certain otheroriginal solutes whose char-
acter has not been determined, as well as" extracted solutes and
suspended particles which have their origin mainly in the tissues
of the fruit outside the juice sacs (1, 3). These extracted soluteq
may include pectin, glucosides, aldehydes and enters; and the
suspended particles may consist of plastid pigments, citrus oil
(in some methods of preparation), and macerated and torn tissue
fragments of various sizes derived from the various tissues of
the fruit. Extracted citrus juice is apparently a colloidal system
and as such shows marked individuality from sample to Fample.
Like most fluids of biological origin, prepared citrus juice is
unstable in nature and has a tendency to become a stable system.

MATERIALS AND METHODS
In this section only such methods will be described as are
general for the experiments reported herein. Special technique
for the investigation of various, phases of the work is treated
with the particular subject concerned.
Type, Variety and Source of Fruit.--The fruits used were
grown in various parts of Florida. Satsuma oranges were ob-
tained from Glen St. Mary, Green Cove Springs, Pensacola,
Marianna and Gainesville. Parson Brown oranges were obtained
from Lake Alfred and Lady Lake, Hamlin oranges from Grand
Island, Washington Navel oranges from Gainesville, and Pine-





Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 9

apple oranges from Lake Alfred. Tangerines were obtained
from Bartow, Hawthorne and the Experiment Station at Gaines-
ville. Grapefruit was secured from Lake Alfred and Gainesville;
Key limes were obtained from Islamorada; Tahiti limes from
Loughman; and a variant of the Tahiti lime from Homestead.
Maturity of Fruit.-Owing to the fact that the work herein
reported was carried out during a comparatively short period
early in the fruit season, it was impossible to obtain as much
information as was desired on the important subject of maturity.
However, every effort was made to select fruit in such a way as
to cover the subject of maturity as thoroughly as possible; the
samples of Satsuma fruits varied from under-ripe to over-ripe,
and to a lesser extent the same was true of Parson Brown
oranges. The Pineapple and Navel oranges and the tangerines
used in most of the experiments were a little below full maturity.
Since the variety factor is of extreme importance, as many vari-
eties as possible were studied and compared.
Juice Extraction Methods.-Four methods of extracting juice
from citrus fruits were used; one was a control method and the
other three approximated commercial methods. The four meth-
ods are described below:
Method No. 1. This method was used as a check in that juice
obtained by it contained a minimum of material from tissues
other than juice sac tissue and is designated in this bulletin as
"juice from juice sacs only". By this method the juice sacs
are removed from the fruit by first peeling off the outer portions
of the rind containing mainly the oil glands. The outer wall of
the locules with attached inner peel tissue is then pared off by
means of a sharp, stainless steel knife. Care is taken to cut
deeply enough at all points so as to exclude any portions of the
inner peel tissue. The pared fruit is then "sectionized" as is
done in grapefruit canneries. This is done by inserting the knife
blade at the base of the locule along the central axis, and sliding
it outward along the locular wall to separate it from the juice
sac tissue. The other wall of the segment is then separated in
the same way, thus completely freeing the mass of juice-sac
tissue from the locular walls. The collected juice-sac tissue is
wrapped in clean gauze and pressed between porcelain plates.
No metal comes in contact with the juice in this method except
the blades of the stainless steel knives used in paring and sec-
tionizing.





10 Florida Agricultural E.'pic, imlnt Station

Method No. la. A variation of the method described above
was used to some extent in studying the normal physiology of
citrus fruits. In this method the locules (segments) or the peel-
ed halved fruits are pressed between porcelain plates.
Method No. 2. The juice is pressed from the halved fruits
by means of an inverted aluminum cup which holds the halved
fruit and presses it against a metal form having the same shape
as the cup which holds the fruit. The clearance between the
form and the cup is adjusted to a little more than the thickness
of the peel. The shape of the cup and the metal form conformed
to that of the fruit. All parts of this press coming in contact
with the juice are of aluminum alloy.
Method No. 3. The juice is pressed from the whole peeled
fruit by means of a conical worm in a conical fluted housing
having a strainer slot along the bottom and a valve at the end
of the housing through which the pulp passes. This press is
made of iron heavily tinned except on the edges of the worm
and the flutings and these are kept bright.
Method No. 4. The pulp of the fruit is reamed out on a high
speed revolving cone (8). The cone in this reamer is of a stain-
less alloy and the collecting bowl is of porcelain.
Handling the Juice.-In handling the juice after extraction
and prior to storage the procedure was as follows:
The juice is run directly from the extractor through a tinned
wire strainer with 18 meshes to the inch and then into a glass
receptacle from which the juice is transferred to a glass vacuum
flask and vacuumized (39). A vacuum is kept on the flask and
as 200 to 300cc. of juice collects in the upper container it is
transferred to the vacuum flask by opening the glass stopcock.
In this way the juice is under vacuum within two to three
minutes after it has been extracted and usually in much less
time. Juice extracted by method 4 was subject to excessive
foaming during the vacuumizing process. This suggested the
possibility that a great deal of air might be dissolved by the
beating effect of this method. Although the exact importance
of the use of the vacuum is not established it has the advantage
in experimental work of giving samples of juice that contain
approximately the same amounts of air, thus eliminating marked
variations that might be due to unequal aeration. In most of
the experiments the vacuum in the flask was relieved with air
admitted to the top of the flask (not bubbled through the juice),






Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 11

but it was in some cases relieved with other gases, such as car-
bon dioxide, nitrogen, and oxygen.
Containers.-The suitability of glass containers for frozen
pack work has been discussed by Woodroof (43). After extrac-
tion and treatment the juice is placed in 8 or 10 ounce jelly
glasses and capped under vacuum with lacquered caps. A vac-
uum of 27 to 29 inches is drawn on the container for an instant
at the time of capping.' These containers were selected as the
best type for experimental work in that they eliminated the
possible effects of paraffin, paper, air, and absorbed odors. The
8-oz. container was generally used and was filled to 1/4 inch
of the top.
Method of Freezing.-The juice is frozen by immersing the
glasses up to the lids in rapidly circulating brine and then placing
on the lids a metal tank through which brine is also circulating.
The brine temperature is maintained at -200 to -250F. and the
contents of the glasses are completely frozen in about 25 minutes.
After freezing is completed the glasses are removed and the out-
sides rinsed in fresh water to remove the brine.
Storage.-After removal from the freezer the frozen juice
was stored at 0F. Some of the juice was put in similar con-
tainers and, without previous freezing, was stored at 320F.
Defrosting.-The samples of frozen juice were thawed by im-
mersing the containers in running tap water. The cap was not
removed until thawing was complete.
Sanitation.-The fruit was washed prior to extracting the
juice and all containers and extractors were kept thoroughly
clean but were not sterilized.
Analytical Methods.-When juice was first extracted detailed
records were taken on the pH, total soluble acids, total sugars,
and other physicochemical characters as required by the ex-
periments on special phases of the subject. Such records were
again made whenever samples were removed from storage for
testing. The quinhydrone electrode was used in making the pH
determinations (32). Total soluble acids were determined by
titration with sodium hydroxide, using phenolphthalein as in-
dicator, corrections being made for temperature differences.
The results are expressed as per centage by weight of anhydrous
citric acid of the expressed juice.
1Equipment for capping the containers loaned by courtesy of the Anchor
Cap and Closure Corporation of Long Island, New York.





Florida Agricultural Experiment Stf t;ti,,


Specific gravity was determined by means of an hydrometer to
0.001, corrections being made for temperature differences. The
600
results are expressed at 6 and also have been converted to
60
the corresponding approximate values for degrees Brix for pur-
poses of comparison with results appearing in the literature
(7, 10, 34, 35).
The method of separating the fruit into its component complex
tissues (33) and then determining the effect of the constituents
of the various fractions on the relatively pure juice, was used.
It was of course impracticable to separate out single tissues and
in carrying on the work groups of allied tissues were considered,
.such as locular walls, albedo, or outer peel as shown in Fig. 1.
In the discussion each of these groups of tissues is referred to
as a tissue. Eight such tissues were considered:
1. Outer peel (epidermal layer with some inner peel at-
tached).
2. Inner peel and veins (albedo).
3. Locular walls.
4. Central axis.
5. Seed coat.
6. Cotyledons and germ.
7. Empty juice sacs.
8. Juice expressed from filled juice sacs only.
Infusions were made by grinding up equal portions by weight
of the various tissues as listed above with sharp clean sand
in a mortar. These infusions were then made up to volume,
and used as indicated later in this section. Certain of the con-
stituents of the tissues were studied: particularly oil, oil-free
sap from: the outer peel and glucosides from the inner peel
and veins.
Naringin was prepared from. grapefruit according to the
method of Zoller (44); hesperidin was prepared from the sweet
orange according to the method of Wander (40). In the case of
thel characteristic glucoside of Satsuma and of lime, the pro-
cedure ofWander was followed and the purified product obtained
was assumed to be the glucoside.

PRESENTATION OF DATA
The principal changes observed in prepared citrus juices on
aging as related to methods of preparation are those in taste,
color and movement of larger particles in the more or less trans-





Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 13

lucent or transparent suspension medium. While working with
Kawano Wase Satsuma oranges on October 19, 1931, a definite
correlation was established between certain methods of prepara-
tion and the development of a bitter taste and a change in color
(Table I). This opened two fertile fields for investigation. On
the following day the study of the changes in direction and rate
of movement of suspended particles was added as a fruitful field
for research (36, 37).

TABLE I.-CORRELATION BETWEEN METHOD OF PREPARATION AND DEVELOP-
MENT OF BITTER TASTE AND CHANGE IN COLOR; KAWANO WASE SATSUMA
ORANGES; OCTOBER 19, 1931.
Method of I Change in
preparation1 Taste Color I Remarks

No. 1A (check)' Pleasantly tart; Deep chrome (or- Retained good qual-
no bitter taste ange); no change ity in refrigerator
for several days

Pleasantly t a r t Color c h a n g e d Did not develop bit-
No. 2 with added fla- from deep chrome Iter taste on stand-
vor of citrus oil; (orange) to sul- I ing at room tem-
no bitter taste fur (light yellow) perature f o r 2 4
within an hour hours

No. 3 Developed bitter Deep chrome (or- Taste became ex-
taste in 2 hours Iange); no change ceedingly bitter af-
ter 4 hours

No. 4 Developed bitter Deep chrome (or- Taste became ex-
taste in 2 hours ange); no change ceedingly bitter af-
'a I ter 4 hours
'See page 9 for descriptions of methods of preparation.
"In all later experiments Method No. 1 was used as the check treatment;
see page 9.

The effective acidity (pH) and the total soluble acids and solids
of the mixture do not give any ready clue to the cause of the
observed changes, as shown by typical data in Table II. Although
there are perceptible differences with regard to these characters,
there seems to be no definite correlation between the observed
changes in the juice and the differences mentioned. It was
therefore necessary to make an attempt to localize the causes
either in the external environment, in the tissues of the fruit,
or in a combination of the two. After their localization, the
next logical step was to determine the factors involved in bring-
ing about the changes.





TABLE II.-SOME CHARACTERISTICS OF CITRUS JUICES AND THE EFFECT OF AFTER TREATMENT.'
I Method
Type of Citrus Date of After treatment Storage pH Total Sp. gr. Degrees
fruit pre- prepa- period acids Brix
pared ration (days) _
Satsuma (Owari) 11/19/311 1 Original juice 0 3.50 1.020 1.037 9.3
Frozen 6 3.51 .996 1.036 9.0
S2 Original juice 0 3.52 1.000 1.037 9.3
"2 Stored at 32F. 6 3.63 .980 1.038 9.6
Frozen 3.46 .980 1.037 9.3
S" 3 Original juice 0 3.58 1.020 1.036 9.0
S Stored at 32F. 6 3.59 .854 1.037 9.3
Frozen 3.59 .860 1.037 9.3
"" 4 Original juice. 0 3.55 .972 1.038 9.6
S" Stored at 32F. 6 3.53 .942 1.038 9.6
SFrozen 3.54 .935 1.037 9.3

Orange (Pineapple) 11/23/31 1 Original juice 0 3.46 1.260 1.047 11.7
S" 2 0 3.47 1.250 1.047 11.7
SStored at 32'F. 2 3.41 1.490 1.048 12.0
SFrozen 3.45 1.380 1.047 11.7
3 Original juice 0 3.47 1.390 1.047 11.7
Stored at 32F. 2 3.48 1.360 1.048 12.0
"" Frozen 3.38 1.330 1.048 12.0
4 Original juice 0 3.45 1.390 1.047 11.7
Stored at 32F. 2 3.40 1.430 1.048 12.0
SFrozen 3.41 1.360 1.045 11.2
Tangerine (Dancy) 11/23/311 2 Original juice 0 2.95 2.150 1.048 12.0
I" Stored at 32F. 4 2.95 ................. 1.047 11.7
S Frozen 3.02 2.060 1.045 11.2
3 Original juice 0 2.96 2.060 1.048 12.0
Stored at 32F. 4 3.07 2.010 1.047 11.7
Frozen 3.09 2.010 1.045 11.2 S
4 Original juice 0 3.03 2.120 1.048 12.0
"" Stored at 320F. 4 3.01 2.000 1.048 12.0
S" Frozen 3.04 2.030 1.045 11.2
Lime (Key) 7/23/31 2 Frozen 120 2.26 7.080 1.037 9.3
3 2.31 6.650 1.037 9.3
4 1 2.32 6.870 1.038 9.6
1Similar data were compiled for Kawano Wase Satsuma; Valencia, Parson Brown, Washington Navel and Hamlin Sweet
Orange; and Tahiti lime.
'Two samples of shorter storage period gave same results.





Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 15

The results are presented under the three headings-(a)
changes in taste, (b) changes in color, and (c) changes in the
direction and rate of movement of suspended particles.

CHANGES IN TASTE
Undesirable tastes developed in prepared citrus juices on
aging, as reported in the literature up to 1925, are described as
stale, bitter, limey, musty and "turpentine" (25, 12). These
terms may not be strictly applicable to the product put up under
the new frozen pack method. In the case of juices put up in
glass containers by the new method, one of the chief difficulties
encountered up to the present is the development of a bitter
taste (8). As shown in Tables I and VIII this bitter taste de-
velops relatively soon after the extraction of the juice, if the
method of preparation is a predisposing factor. However, such
other factors as temperature of storage and maturity of the
fruit must be considered also in this connection. While other
undesirable flavors may develop in the frozen or cold stored juice,
this preliminary report deals primarily with the definitely bitter
taste which is apparently the same as that mentioned by Chace
and Poore (8).
Tasting Technique.-As a rule the results presented are based
upon tasting of the juices by two or more individuals. An at-
tempt was made to use constant quantities of materials for
tasting purposes in any particular experiment. The degrees of
taste difference are indicated on a relative basis only. When
any particular taste was present in a pronounced degree, the
same was indicated with a (+) sign. Decreasing degrees of any
particular taste are indicated by (+ -), (+ -), etc.; in-
creasing degrees are indicated by (+ +), (+ + +), etc.
Bitter Taste.-A clue to the localized tissues responsible for
the bitter taste which develops in citrus juice prepared by cer-
tain methods was definitely indicated in the preliminary ex-
periments (36, 37) reported in Table I. The difference in taste
was due to method of preparation and this indicated that the
cause of the trouble could possibly be traced to certain of the
tissues of the fruit. While still in the whole fruit these various
tissues are effectively separated from each other. However,
as indicated in the previous discussion, the juice extraction
process tears down these barriers more or less completely and
breaks up the tissues to a greater or lesser extent, depending on





Florida Agricultural Experiment Station


the method, and the resulting juice may be a mixture of ma-
terial from most of the tissues. Once the juice is prepared
in a manner favoring the development of the bitter taste, other
factors may enter which may delay or modify the degree of its
development under any particular conditions of after treatment.
Although it was suspected that the causal agent might be of
glucosidal nature, the plan of procedure included a comprehen-
sive study of other possible causes. The mechanism involved
could be either (a) enzymatic or (b) non-enzymatic. The fol-
lowing lines of investigation were followed in an attempt to
determine the source of the undesirable tastes: (a) Localiza-
tion of the cause in the tissues; (b) determination of the nature
of the mechanism involved (whether enzymatic, non-enzymatic,
or solution); (c) determination of. effect of variety, maturity
and quality of fruit, and (d) determination of effect of after-
treatment (such as freezing and storing).
Localization of Causal Agent or Agents.-It was necessary
to consider as many tissues of the citrus fruit as possible so that
no important source of the trouble would escape the investiga-
tion. The tissues which were obviously of no importance were
quickly eliminated, but a more detailed study of the remaining
tissues was made with the object of localizing the cause or
causes in a definite region or regions of the fruit.
To eliminate from the study the tissues which did not appear
to contain the causal agent for the bitter taste, infusions were
made by adding macerated tissues to the juice and testing for
the effect on bitter taste development when diluted with citrus
juice. The check treatments consisted of similar dilutions using
tissue infusions made with water. Since the degree of dilution
necessary to secure sufficiently marked results, if any, was
unknown, three degrees of dilution were included in the first
experiment-2, 4 and 8 parts of tissue infusion to 100 parts of
juice pressed from juice sacs only.
The data in Table III show that the tissues most likely re-
sponsible for the development of the bitter taste are the inner
peel and veins, the outer peel and the locular walls. The respec-
tive degrees of bitterness developed under the experimental
conditions (dilution 8 parts of infusion to 100 parts juice) were
for the freshly prepared infusion of outer peel (+ --) and for
the same infusion after standing (+); and for the inner peel
and locular walls (+) when freshly prepared infusion was tested






Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 17

TABLE III.-LOCALIZATION IN THE TISSUES OF THE SATSUMA ORANGE FRUIT
(KAWANO WASE) OF THE CAUSE OF THE BITTER TASTE, OCTOBER 28, 1931.
(DILUTIONS MADE WITH JUICE PRESSED FROM JUICE SACS ONLY).


Infusion
Tissue Extractive
used


Pts. infusion
per 100 pts.
liquid


Outer peel Water 2
4
8" 8

Juice 2
4


Inner peel and Water 2
veins 4
it 8

Juice 2
4
c 8

Locular walls Water 2
4
cc 8

Juice 2
4
_" 8

Central axis Water 2
4
c 8

Juice 2
4


Seed coat Water 2
4
8

Juice 2
4
8

Cotyledons Water 2
and germs 4
8 8

Juice 2
4
8


Bitter taste developments'

Immediate | Later



+- +-


+- +-
+ +


-

-


+-

-4--


++

+f


I ~--


1Relative taste differences are indicated as follows: (-) indicates ab-
sence of the bitter taste; (+-), (+), (++), etc:, indicate relatively
greater degrees of the bitter taste.


~






Florida Agricultural Experiment Station


and (+) for the same infusion after standing. The tastes given
by the seed coat and cotyledons plus germ were of a different
nature than the one sought; the central axis and juice sac in-
fusions were practically tasteless, except in certain varieties of
such citrus types as the grapefruit (see Tables V, VI, VII, and
VIII). In this fruit the vascular tissues connecting with the
juice sacs are much coarser than is the case in some other citrus
types and the juice expressed from the separated locules thus
carries more of the materials commonly associated with the
inner peel and locular wall. The juice sacs themselves are rel-
atively coarse in structure and may contain the bitter principle.
After the elimination of other tissues the work was concentrated
on the tissues of the inner peel, locular walls and outer peel.
In further experiments, infusions made with outer peel from
which the adhering portions of the inner peel had been more
carefully removed failed to give a detectable bitter taste, though
this taste may have been present in very small amount and mask-
ed by the oil taste. As a result of these experiments the outer peel
was eliminated from the study as not being important in pro-
ducing the bitter taste. Up to this point all the fruit used was
below full maturity. In later experiments with riper fruit it
appeared that the locular walls were probably less important
as a source of the bitter taste than were the inner peel and
vein tissues.
The next step was to determine the factors involved in bring-
ing about undesirable taste developments in prepared citrus
juices, from the standpoint of the presence or absence of inner
peel and veins or locular wall tissue.
The tests for the enzymatic factors proved negative. The
work of Reed (31) and McDermott (39) on the inactivation of
oxidases and peroxidases in citrus juices was verified, as shown
in Table IV. The experiment included a study of (a) the dis-
tribution of oxidase and peroxidase in the locular walls, inner
peel, veins, and outer peel (26); (b) the effectiveness of water
and juice in extracting possible enzymes; (c) the effect of Berke-
feld filtering and centrifuging tissue extracts made with water
and juice, and (d) the effect on oxidase and peroxidase ac-
tivity of mixing water extract of inner peel plus veins (giving
positive reaction for oxidase and peroxidase) with the original
juice, Berkefeld-filtered juice, and centrifuged juice.
In the above experiment, all water extracts-untreated, Berke-
feld-filtered and centrifuged-gave positive tests for oxidase




TABLE IV.-REGIONAL DISTRIBUTION OF OXIDASE AND PEROXIDASE IN.THE TISSUES OF THE SATSUMA ORANGE FRUIT
(KAWANO WASE); 11-2-31.


Infusion


Tissue
extracted

Locular walls


it
it
Inner peel and
veins (a)







Outer peel


Extractant After
used Treatment

Water Untreated
Berkefeld filtered
Centrifuged
Juice Untreated
Berkefeld filtered
Centrifuged

Water Untreated
Berkefeld filtered
Centrifuged
Juice Untreated
i" Berkefeld filtered

S Centrifuged

Water Untreated
Centrifuged
Juice Untreated
S Centrifuged


]Oxidase (Guaiacum test)(Peroxidase (Guaiacum )


Not boiled

Blue
Light blue
Faint blue
Negative
Faint blue
Negative

Blue
Faint blue
Faint blue
Negative




Faint blue
Light blue
Negative
4C


Check
(boiled)


Negative





4(

it
it


Not boiled


Intense blue
Medium blue
Medium blue
Negative
Light blue
Negative

Intense blue
V. light blue
Medium blue
Negative
it



Intense blue
Intense blue
Medium blue
Medium blue


Other mixtures tested I


Original juice (b)
Original juice (c)
(d)


- Berkefeld filtered
- Centrifuged
- Untreated


Juice poured off parings of inner peel
and veins

Juice poured off locular walls
Mixture of (a) and (b)1
"(a) and (c)'
(a) and (d)1


Negative



cc
"

"u


Negative
it
"


Negative
cc
tt





it
cc
cc
"

"C

"C


Check
(boiled)


Negative













iC
it


Negative
"


Remarks


ISame filter used
I as in water sam-
ple




Not kept in cold
storage.
Not kept in cold
storage


1Dilution: 1 part infusion to 8 parts of juice.
2Infusions made in the proportions: 1 gm. of fresh tissue to 1 cc. extractant.






20 Florida Agricultural Experiment Station

and peroxidase activity; however, the last two gave color reac-
tions to a lesser degree. Juice extracts, as a general rule, gave
either negative or contradictory results; untreated juice and
centrifuged juice extracts gave negative tests for these en-
zymes, except in the case of outer peel extract; and Berkefeld-
filtered juice extract gave contradictory results. Water extracts,
whether Berkefeld-filtered, centrifuged or untreated, when mixed
with original Satsuma juice gave negative tests, indicating that
the degree of acidity (pH 3.3 in this case) inactivates the en-
zymes present in the tissue extracts.
TABLE V.- TESTS TO DETERMINE THE NATURE (ENZYMATIC OR NON-
ENZYMATIC) OF THE BITTER TASTE DEVELOPMENT IN CITRUS JUICES.

Infusion Bitter taste,1 etc., developed'
Extractant Inner peel and Satsuma orange Sweet orange
u veins added Kawano Wase Parson Brown
use (gms.) 11/9/31 11/10/31

Juice" None -
0.01 +-
S0.10 + -
S1.00 + +
5.00 + + + +
S1.00 boiled' + +
Boiled juice2 None -(+ boiled taste) -(++ boiled taste)
S 1.00 ++(+ boiled taste) +-(++ boiled taste)
1.00 boiled3 +++(+ boiled taste) ++(++ boiled taste)
Water None -
0.01 + +--
0.10 + +
1.00 + + +
5.00 + + + + +
1.00 boiled' + + + + +

1Relative taste differences are indicated as follows: (-) indicates
absence of the bitter taste; (+-), (+), (++), etc., indicate increasing
degrees of the bitter taste.
2Juice pressed from juice sacs only.
'Heated to boiling point.
'Data taken within 15 minutes after mixing, and re-checked after 24
hours.

The presence of glucosidases was investigated from the stand-
point of possible change in optical activity of clarified juice
from juice sacs only when tissue-infusions possibly containing
glucoside splitting enzymes were added to the same (16). The
determinations were made with a polarimeter. The tests proved
negative. Any changes observed were 'well within the possible
error of the experiment.






Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 21

The possible causal relation between other enzymes and the
development of bitter taste was tested for by adding boiled
tissue to unboiled juice and vice versa, and also by boiling both
before mixing. The tests gave negative results from the stand-
point indicated, as shown in Table V. There was no decrease
but rather an increase of the bitter taste due to boiling.
The evidence apparently points to the possibility of a non-
enzymatic mechanism as causative. Experiments to test this
hypothesis were conducted along three lines; (a) testing the
possible identity of the causal, agent for bitter taste with gluco-
sides; (b) determining the effect on taste of varying amounts of
glucoside, and (c) the effect of the pressure and temperature
factors on the degree of bitter taste developed in prepared citrus
juices. The solubility of the substance causing the bitter taste
was also investigated.
Aliquots of the various tissue extracts were centrifuged and
Berkefeld filtered, and similarly, aliquots of the juice used for
dilution in the case of locular walls and inner peel and veins
infusions were centrifuged and Berkefeld filtered. The centri-
fuging and Berkefeld filtering processes did not seem to remove
the causal agents of the bitter taste, since treatments consisting
of Berkefeld-filtered infusions diluted with similarly treated
juice expressed from juice sacs only still gave mixtures which
developed a bitter taste. As a result of these experiments it
appeared that the cause of the bitter taste was a soluble sub-
stance.
When the experiments were undertaken it was suspected that
the causal agent for the bitter taste developed in citrus juices
was of glucosidal origin, as mentioned in an earlier discussion.
However, it was necessary to eliminate other possibilities to se-
cure reasonable assurance that the original hypothesis might
prove tenable.
The data presented in Tables V and VI indicate that the de-
gree of bitterness developed, when inner peel and veins tissue
or naringin is added to Satsuma juice pressed from juice sacs
only, is in a marked degree proportional, within the limits of
the experiment, to the amount of inner peel and veins tissue or
glucoside added to juice expressed from juice sacs only. In the
case of grapefruit the bitter taste is present even in juice ex-
pressed from juice sacs only, but the degree of the characteristic
bitterness may be increased as shown in Table VI by adding
naringin.










TABLE VI.-POSSIBLE IDENTITY OF THE CAUSAL AGENT FOR BITTER TASTE WITH GLUCOSIDE.


Solution
Degree saturation
Solvent used of naringin'
solution

Juice" None
0.0001
0.001
t" 0.01
0.1
Saturated

Boiled juice" 0.0001
0.001
0.01
0.1
Saturated

Wpter (check) None
0.0001
0.001
0.01
0.1
Saturated


Satsuma orange
(Kawano Wase)
11/10/312



+-
+++


boiled
it
"


(+
(+
(f
+f (~
~++ c-;t-


taste)
)
)
)
)


+-

+++


'Relative taste differences are indicated as follows: (-)
indicate relatively greater degrees of the bitter taste.
'Experiment set up 11-9-31.
'Naringin prepared according to method of Zoller (44).
'First one-third pressings used in this experiment.
'Juice pressed from juice sacs only.


Bitter taste,1 etc., developed
Grapefruit (Silver Cluster4)
11/18/31 1 11/20/31


+
+
++
+++
++++
++++

+(+ boiled taste)

-+(+ )


+-
~+


++
+++
+++
+++
++++
+++++
+(+ boile


++++ (++


-
++
++
+++
++++


indicates absence of the bitter taste; (+-), (+), (+


5






d taste)

" )
a





ti
-/2

+), etc.,










TABLE VII.-THE EFFECT OF THE CHARACTERISTIC GLUCOSIDE AND THE GLUCOSIDE-FREE TISSUE ON THE DEVELOPMENT OF
THE BITTER TASTE1 IN PREPARED CITRUS JUICES.


Taste
Variety Solvent untrue
solve

Satsuma (Owari) Juice -
12/4/31 Water -
Orange (Parson Juice' -
Brown) 11/12/31 Water -
Orange (Hamlin) Juice4 -
12/4/31 Water -
Grapefruit (Silver Juice' +
Cluster) 12/4/31 Water -
Lime (Key) Juice' -
12/4/31 Water -
Tangerine' (Dancy) Juice' -
12/4/31 Water -


STastes developed when varying Tastes developed when varying amounts
ted amounts of glucoside were added of glucoside-free tissue were added
nt 1 1/100 1/10 I


'Relative taste differences are indicated as follows: (-) indicates absence of the bitter taste; (+-), (+), (++),
etc., indicate relatively greater degrees of the bitter taste.
2Tissue before extracting (1 gm.) gave +.
8Naringin was used; characteristic tangerine taste present in all juices.
'Juice pressed from juice sacs only.







TABLE VIII.-BrTTER TASTE DEVELOPMENTS1 IN PREPARED CITRUS JUICES IN RELATION TO METHODS OF PREPARATION,
FREEZING AND STORAGE.2


Type of citrus
fruit


Satsuma (Owari)
it

cc
cis

"'
"




Orange (Parson Brown)
Lady Lake
it



Orange (Parson Brown)
Lake Alfred
cc
it


Date
pre-
pared
(1931)

11/19
it
it
cc
cc
it
It
it
tt


it

11/13
it



11/14
"u
"


"t


Method
of
prepa-
ration

1

2


3


4
it
is

2

3
S'
4
it

2
it
3

4


After
Treatment


Original juice
Frozen
Original juice
Stored at 320F.
Frozen
Original juice
Stored at 32'F.
Frozen
Original juice
Stored at 32F.
Frozen

Original juice
Stored at 32F.
Original juice
Stored at 32F.
Original juice
Stored at 32F.

Original juice
Stored at 32F.
Original juice
Stored at 32F.
Original juice
Stored at 32F.


Bitter taste developments at different samplings
Figs. in () refer to hours after experiment was set up


Stor-
age
per'd
Days

0
6
0
6

0
6

0
6


0
2
0
2
0
2

0
2
0
2
0
2


1st 2nd

- (%)-


(Y2)-
(%)-
*


(1/2)+-
(%)+-
+- ('2)+-


+- (%)+


- (2)-

- (2)-
(2)-
*


(2) -
(3)-
(2) +-
(3)+
(2) +-
(3)+-


4th

(3)-
(3)-

(3)-
(3)-

(3)++
(3)+--
(3)+
(3)++
(3)+-


5th 6th

(16)-
(5)-

(4)-
(4)+---

(5)+++
(5)+-
(5)+
(5)++
(5)+-


*No records taken.
'Relative taste differences are indicated as follows: (-) indicates absence of a bitter taste; (+-), (+), (++), etc.,
indicate relatively greater degrees of the bitter taste.
"Similar data for Owari and Wase Satsuma (11/19/31 and 11/13/31); Hamlin sweet orange (11/20/31); Pineapple
sweet orange (11/23/31); Washington Navel orange (11/14/31); and Tahiti lime (7/22/31) were secured but are omitted
from this table since the results are similar.
aTwo samples of shorter storage period (1 and 2 days) gave same results.


3rd

*
*
(2) -
(1%))-

(2)+
(1Y4)+


(14)+
(1i4)+-


(3)

(3)-

(3)-




TABLE VIII.-BITTER TASTE DEVELOPMENTS' IN PREPARED CITRUS JUICES IN RELATION TO METHODS OF PREPARATION, FREEZING
AND STORAGE'.-Continued.


Type of citrus
fruit


Orange (Washington Navel)

"4


Lime (Tahiti)'


Lime (Key)"


Date
pre-
pared
(1931)

11/19
it






11/23








11/18
it

"t
t"


Method
of
prepa-
ration

2
it
3


4
i"

1
2
it
3
4


4
4
it
tt

2
3
4
2
3
4


After
Treatment


Original juice
Stored at 32'F.
Frozen
Original juice
Stored at 32'F.
Frozen
Original juice
Stored at 32F.
Frozen
Original juice

Stored at 32*F.
Frozen
Original juice
Stored at 32*F.
Frozen
Original juice
Stored at 32F.
Frozen
Original juice
"1


Stor
age
per'
Day


- Bitter taste
d Figs. in () ref4


s 1st


++
+-
++
+




+--
+
+
+



+-


I 2nd

*
*

(%)+-

(%)+
(%)+-
*
(%)+
(4)-
(2)-
(%)--


(%)++
(%;)+
(%)+
(%)+


developments at different samplings.
er to hours after experiment was set up
S 3rd I 4th I 5th I 6th


(1)-

(1)+---
*
(2)++


(2)+++


(5)-
(1)-
(1)+---
(6)++++
(1)+

(1)++
(1)+
(1)+


(5)-
(5)-
(5)+-
(5)+

(5)+++
(5)+

(5)+++

(7)-
1(3)-
(3)+-
(8)+-

(3)+
(3).+++
(7)+++
(3)+
(3)++


(6)-


*No records taken.
'Relative taste differences are indicated as follows: (-) indicates absence of a bitter taste; (+-), (+), (++), etc.,
indicate relatively greater degrees of the bitter taste.
'Similar data for Owari and Wase Satsuma (11/19/31 and 11/13/31); Hamlin sweet orange (11/20/31); Pineapple
sweet orange (11/23/31); Washington Navel orange (11/14/31); and Tahiti lime (7/22/31) were secured but are omitted
from this table since the results are similar.
'One sample of shorter storage period gave same results.
"Juice diluted 1 part juice to 10 parts water before tasting.


Tangerine
"


"4

(Dancy)


I I


I I






Florida Agricultural Experiment Station


A more comprehensive experiment which verifies these con-
clusions was carried out with Satsuma orange, sweet orange,
grapefruit, lime and Dancy tangerine (Table VII). In the ex-
periment the juice from juice sacs only was treated in two ways
-(a) by the addition of the glucoside extracted from the inner
peel and veins; (b) by the addition of the glucoside-free inner
peel and veins tissues. The data show that the juice which
received the glucoside-free tissues gave negative results except
in the case of grapefruit juice, which result is in harmony with
previous experiments. The addition of the extracted glucoside
gave positive results, the degree of bitterness increasing with
the amount of glucoside added.
The data presented in Tables V, VI and VII indicate that the
major cause of the bitter taste developed in prepared citrus juices
on aging is apparently of glucosidal origin. Since the chemical
structure of the glucosides contained in various types of citrus
is not the same, it would be expected that the bitter tastes asso-
ciated with them would not be identical. This is actually the
case, and each glucoside or closely related group in so far as
tested can be recognized by its characteristic taste qualities.
The data presented in Tables V and VI indicate also that the
storage temperature factor may be of importance with reference
to the rate of bitter taste development and the final value at-
tained. The figures in Table V show that the degree of bitter
taste developed is markedly greater in cases where either the
juice, the tissue, or both are heated before or after mixing. The
figures presented in Table VI although not as conclusive as those
presented in Table V, show that apparently more naringin goes
into solution as the temperature is raised, as indicated by in-
creased bitterness of taste after boiling. This is in harmony
with the work of Zoller (44) who has shown that naringin is
more water-soluble at higher temperatures.
The data presented in Table IX indicate that the degree of
bitterness developed when juice is expressed by means of por-
celain plates from inner peel and veins tissue with attached
juice vesicles, is in a marked degree proportional to the pressure
exerted. The first 100 cc. develops the least bitter taste and
usually the degree of bitterness rises markedly in the case of
the third 100 cc. It should be pointed out that when juices are
expressed from juice sacs only, except in the case of the grape-
fruit, a bitter taste does not normally develop, even with eight
or nine days cool storage. This would indicate that the data in






TABLE IX. EFFECT OF VARIOUS DEGREES OF PRESSURE AND STAGE OF MATURITY ON DEVELOPMENT OF BITTER TASTE IN
PREPARED CITRUS JUICES.


-I ITaste developments'
Type of citrus fruit Date Stage of maturity Nature of Press- After After After a
I II tissue ings Initial 4 hrs. 8 hrs. 12 hrs. 20
Si


Satsuma (Owari)


Orange (Hamlin)

c c


Tangerine (Dancy)





Grapefruit (Walters)


1/ Inner peel
12/ 3/31 Relatively mature and locular
walls

S Locular
walls

Inner peel
and veins
Locular
walls and
inner peel
and veins


Relatively immature Locular
walls

S Inner pee 1
and veins
Relatively immature
11/18/31 (from Station Juice sacs
grounds)


.1ISI


1St
2nd
3rd


1st
2nd
3rd
1st
2nd
3rd

1st
2nd
3rd


1st
2nd
3rd


+-----
+-- +--+--
+-- +-- +-


+
+
++


++
++
+++


++
++
+++


1st +- +
2nd + ++
3rd + +++
1st + *
2nd +++ *
3rd ++++++ *


*


*
* 4


++ *
+++ *
+++ *
*
*
*


-I


r--
+--
+-


*No observation recorded.
'Relative taste differences are indicated as follows: (-) indicates absence of a bitter taste; (+-), (+), (++), etc.
indicate relatively greater degrees of the bitter taste.
'Tissues consisted of outside parings from peeled fruit (inner peel and veins, plus top of locular walls), central axis
plus radial locular walls with remaining attached juice sacs; or juice sacs as indicated. -
'Ilst" indicates first 100 cc. of one pressing; "2nd" indicates the second 100 cc. of the same pressing; "3rd" indicates
juice sample obtaini.i by repressing. Pressings made between porcelain plates.
'Juice stored at 40" to 500 F.


to
I3


After to
hrs.'
+-
.+
+

4-
+-
+--
-- ++
+---- (


+--?

+++
+++


-+++

-++++ g


.


I


|
1
|


I


I


.





Florida Agricultural E., p .ii, r tt Station


Table IX possibly should be interpreted on the basis that the
bitter taste is due to glucosidal material in solution pressed
primarily from the cells of the inner peel and veins and locular
wall tissue.
Type, Variety, Quality and Maturity Factors.-The data pre-
sented in Tables I to IX inclusive, are in harmony with the com-
monly accepted ideas regarding the wide differences in kind of
juice secured from various types of citrus fruits, such as Sat-
suma orange, sweet orange, tangerine, grapefruit and lime. The
chief variations such as effective acidity (pH), total soluble acids
and solids, as well as the more subtle taste qualities associated
with each type, are due to the type of citrus fruit utilized.
Within a citrus type the effect of variety on the quality of the
juice is of great importance.
In the case of the Satsuma orange two varieties have been
studied. Juice of Kawano Wase Satsuma oranges was prepared
on October 19 (Table I). A marked bitter taste developed in
this juice within two hours. With reference to Owari Satsumas,
the results are somewhat different. Juices were prepared from
fruits of average maturity from Marianna on November 19
(Table VIII). Fruits of advanced maturity from the Station
orchard at Gainesville were used to prepare juices on December
3 (Table IX). In the case of the two samples of average matur-
ity prepared by Methods 3 and 4 a bitter taste was developed to
the degree of (+) at the end of 4 hours; the sample of advanced
maturity from the Station grounds gave a bitter taste only to
the degree (+ -), even when the juice was pressed from
inner peel and veins parings, as indicated in Table IX.
As shown in Table VIII, the juice of the Washington Navel
orange has a greater tendency to develop a bitter taste than juice
of Parson Brown, Pineapple and Hamlin oranges. In the case of
grapefruit the glucoside taste is expected and there is even a
prejudice against such a variety as Triumph which does not have
the characteristic glucoside bitterness of this type of citrus. The
subl.ect, of the effect of quality of fruit within a variety in this
particular has not been explored from the experimental view-
point.
In most ca-es the bitter taste developed in sweet orange juice
\\wn found to Ibe relatively little and this was found to decline
with advancing maturity. In Table VIII it will be noted that on
November 13 and 14 samples of juice were prepared from Parson
Brown oranges. .'The first sample was prepared with fruit from





Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 29

Lady Lake, Florida, and the second with much less mature fruit
from Lake Alfred. The first sample developed no noticeable
bitter taste but the second sample a degree of bitterness for
Methods 3 and 4 of (+ -) after two hours of standing, thus
indicating the effect of maturity. Pineapple and Hamlin orange
juice prepared by Methods 3 and 4 gave results very similar to
these. In the case of Washington Navels, however, an increased
bitter taste was found. Juice prepared from this variety on
November 14 and 19 developed a degree of bitterness for
Methods 3 and 4 of (+ +) and (+) after two hours for the first
date and a degree of bitterness amounting to (+) for both
methods after standing for five hours for the second date (Table
VIII).
The tangerine juices prepared on November 23 gave results
closely paralleling those for Satsumas, developing a very bitter
taste after standing for several hours (Tables I, VIII and IX).
Tahiti and Key lime juices prepared on November 18 by Methods
3 and 4 developed a distinctly disagreeable bitter taste (Table
VIII).
The results discussed are, of course, a mere beginning toward
the thorough description of citrus varieties suitable for juice
production on the basis of glucoside content and other con-
stituents and the relative proportions of these remaining at
various stages of maturity. The subject is of major importance
and will require numerous comprehensive experiments to de-
termine the best varieties for juice purposes and the optimum
stage of maturity.
The preliminary results are in harmony with those often
quoted in the literature to the effect that a bitter taste does not
always develop or that properly matured fruit does not give a
poor quality juice (25, 8, 11)." The experiments here reported
2After the first draft of this bulletin was completed one of the authors
happened to come across the following interesting observation in Bonavia's
Oranges and Lemons of India, 1888 (3): "I have tasted the pulp of many
Sevilles in various parts, and rarely have I found the pulp bitter. It is
simply sour. Sometimes I thought the pulp had a "soupgon" of bitterness
in it, but very rarely. I think the mistake, if it be a mistake, has arisen
from the way of tasting the pulp. If you cut a Seville orange in two trans-
versely, and then give the pulp a bite, you will probably say it is bitter.
But in biting the pulp with the upper teeth, your lower teeth and lips
graze against the rind, which is intensely bitter, aromatic and pungent.
The bitterness of the rind mixing with the juice in the mouth makes you
think the pulp is bitter-sour. While if you use a spoon and scoop out a
bit of the pulp without touching the rind and taste it, you will probably
say it is only sour." As a footnote to the above Bonavia explains that
"possibly the envelopes of the quarters, or carpels, in which the juice ves-
icles are contained, may sometimes be bitter."





Florida Agricultural Experiment Station


support these empirical statements and will make it possible
after the subject is thoroughly investigated from this viewpoint
to select citrus fruits intelligently so as to reduce to a minimum
the bitter taste in the product. In determining the exact range
in the maturity of citrus fruits within which material should be
selected for juice extraction, two opposing tendencies must be
considered. While the glucoside content decreases with age
(44), as a general rule the processes of senescence become in-
creasingly important, predisposing the prepared product to un-
desirable qualities other than the bitter taste. The exact range
of maturity within which the fruit should be selected will depend
not only on the variety but also on local environmental dif-
ferences which would tend to shift the period in one direction
or the other. The rule that should be followed in each case is
to harvest the fruit when the glucoside content has decreased
sufficiently to reduce the tendency of the product to the develop-
ment of a bitter taste to the minimum and before the processes
of senescence have proceeded far enough to bring other undesir-
able qualities into the product.
Effect of After Treatment of Juice on Development of Bitter
Taste.-With the exception of the cases in which the original
gases were removed from the juice and replaced with others or
where the juices were homogenized by treatment in a colloid mill,
the after-treatment was uniform. The vacuumized juice was
poured into 8-oz. jelly glasses and again vacuumized during the
sealing process. The product was then stored in two ways-
(a) at 320F. (0C.) without preliminary freezing, and (b) at
0F. (-180C.) with preliminary freezing. Samples were then
removed at convenient intervals for investigation. The object
of the first treatment, storage at 320F. (0C.) was to test out
the possibility of devising a method of preserving the juices for
short periods up to 36 hours in order to meet the demand of
the producer who wishes to market unfrozen citrus juices shortly
after extraction. The second treatment, preliminary freezing
with storage at 0F. (-180C.) is intended to meet the demand
for a feasible method of storing the product over a period up to
eight months or longer.
In the case of unfrozen juice stored at 320F. (0C.) for short
periods, up to the present, satisfactory results have been ob-
tained with Methods 1 and 2 insofar as controlling the bitter
taste is concerned (Table VIII). However, in some instances






Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 31

other undesirable tastes have given some trouble; therefore
Method 2 is feasible with these exceptions. In the case of
Methods 3 and 4, as a general rule, the development of the bitter
taste could not be effectively controlled even by immediate stor-
age excepting in cases where the glucoside was present in min-
imal quantity. As shown in Table VIII the rate and degree of
the development of the bitter taste was not consistently affected
by the treatment. In this connection it should be pointed out
that some of the undesirable tastes, especially when present in
minor quantities, are not readily distinguished when the product
is consumed in the cold condition. This would indicate that the
taste would likely be less pronounced in actual commercial prac-
tice if the product were produced and marketed under low tem-
perature conditions. However, it would be necessary to indicate
to the consumer that the product might deteriorate rapidly at
ordinary room temperatures.
When citrus juices are frozen and stored at o0F. (-180C.)
partially satisfactory results have been obtained in all cases by
the use of Methods 1 and 2. Valencia orange and Tahiti lime
juice put up by Method 2 had developed no bitter taste even
after four months of storage at 100F. (-120C.) in the frozen
condition. However, lime juice prepared according to Method
4, after four months' storage developed a perceptible bitter taste
within an hour after defrosting. The results secured by storing
juices in the frozen condition at o0F. (-180C.) for shorter
periods in the case of various types of citrus including Satsuma
orange, sweet orange, Dancy tangerine, and lime were similar to
those reported above for Valencia orange and Tahiti lime over
a longer period.
Other Tastes.-Of the various other tastes, desirable and other-
wise, only that imparted by the addition of citrus oil is taken up
in this report. A minimum addition of citrus peel oil to the
freshly extracted juice is not objectionable and in fact is usually
preferred. While the presence of a small amount of oil has not
had any bad effect on juice frozen by certain methods it might
result in undesirable tastes under some other methods of freez-
ing and storage. After four months storage Valencia orange
and Tahiti lime juice extracted by Method 2, frozen and stored
under vacuum had only the very slightest off-taste, though
there was a considerable oil content. In connection with the
bitter taste, as pointed out in the preceding discussion, a mini-





Florida Agricultural Experiment Station


mum amount of citrus oil may entirely mask the small amount
of bitter taste developed in juices prepared by some methods
of manufacture.
CHANGES IN COLOR
Next in importance after taste comes the color of prepared
citrus juices. The orange or yellow coloring matter of the flesh
of various citrus types is localized in small bodies called plastids
found in the cells which compose the juice sacs of the fruit
(23). The plastids are apparently of various shapes, depending
on the particular type of citrus fruit under consideration.
The red, orange and yellow pigments occurring in plants ap-
parently fall into several chemical classes: carotinoids, flavones
(anthoxanthones) and anthocyanins. The presence of the carot-
inoids has been demonstrated in certain citrus juices by Matlack
(24). Under the head of carotinoids are included all red, orange
or yellow pigments extracted by fat solvents from plant or
animal tissues. As a class, the free flavone pigments are almost
insoluble in water, slightly soluble in ether, and easily soluble in
hot alcohols and alkalies (42, 41, 28). With alkalies they give
a brilliant yellow color, a property that may be used for their
detection in tissues of plants in the absence of such glucosides as
hesperidin and naringin. The anthocyanins of plants are red,
blue and purple pigments soluble in water and dilute alcohol;
insoluble in ether; are turned red by acids and blue or green by
alkalies (27).
The subject of changes in color of prepared citrus juices is
presented under the following heads: (a) possible nature of
plastid pigments in juice sacs of citrus fruits; (b) effect of citrus
oil and other compounds on the color of prepared citrus juices,
and (c) effect of method of preparation, freezing and storage on
color of prepared citrus juices.
The color changes in citrus juices were studied on two types
of material-empty juice sacs and the juice containing the ex-
tracted plastid pigments.
Color descriptions are based on the Maerz and Paul color
dictionary (22). Two types of material were described as to
color. In one case the pigments were in solution and in the
other the colored particles were suspended in the juice mixture.
An 8 oz. tumbler was filled to a depth of 3/4 inch, and the mask
was placed over the top of the tumbler which was set on a 600 cc.
beaker inverted over a white background. This allowed light to






TABLE X.-SOLUBILITY TESTS ON THE PIGMENTS OF EMPTY JUICE SACS OF VARIOUS CITRUS TYPES.

Satsuma (Owari) I Sweet orange (Hamlin) Tangerine (Dancy)
Solvent Solu- Original Color Solubility Original Color of Solu- Original Color of
Group' Solvent ability color of of sacs Color in color of sacs Color ability color of sacs Color
in 50 ce. sacs (10 after of 50 cc. sacs after of in 50 cc. sacs after of
solvent gms.) treatment filtrate solvent (10 gms.) treatment filtrate solvent (10 gins.) treatment filtrate
+ 9-9-L2 I I 9-4-L I 9-4-K
Ethyl + + (Deep 9-5-K [ 9-2-K (L. orange 9-2-K 9-1-I 9-9-1 9-6-L (Orange
Alcohol 95%orange) (Yellow) (Yellow) yellow) (Yellow) (Yellow) (Orange) (Orange) yellow) 1o
9-9-L 9-4-L I 9-5-K
cetone + (Deep 9-3-K 9-2-K (L. orange 9-1- I 9-1-L + + 9-9-I (Orange 9-2-K
o___ _range) (Yellow) (Yellow) yellow () (Yellow) (Yellow) Yelw (Orange) yellow) (Yellow)
9-9-L 9-4-L | 9-4-L 10-1-C | 9-5-K
I. Acetaldehyde + (Deep (L. orange 9-2-J +- |(L. orange 9-1-L (Pale + + 9-9-I (Orange 9-2-K
______o__ __ range) yellow) I (Yellow) I yellow) I (Yellow) yellow) I (Orange) yellow) (Yellow)
S 09-9-L 9-5-K 9 -4-L 10-1-C 9-2-K
Ethyl Ether -- (Deep (Orange 9-2- + (L. orange 9-2-K (Pale + 9-9-I (Orange 9-2-K
orange) yellow) Yellowyellow) (Yellow) yellow) (Orange) yellow) (Yellow)
9-9-L 9-4-L I 9-4-L 10-1-C 9-4-L
Chloroform + (Deep (L. orange1 9-2-J +- (L. orange 9-2-K (Pale + + 9-9-I (L. orange 9-2-K ;
orange) yellow) (Yellow) yellow) (Yellow) yellow) (Orange) yellow) (Yellow)
I 9-9-L 9-4-L 9-4-L |
II. Petrol Ether (Deep (L. orange 9-1-J (L. orange 9-2-K Colorless 9-9-I 9-3-K 10-1
orange) yellow) (Yellow) yellow) (Yellow) (Orange) (Yellow) (Yellow)
9-9-L 9-4-L I9-4-L 10-1-C 9-4-L
Benzene + (Deep (L. orange 9 K (L.orange 9-2-K (Pale + 9-9-I (L. orange 9-2-
orange) yellow) | (Yellow) yellow) (Yellow) yellow) I (Orange) yellow) (Yellow)
9-9-L 9-4-L I 9-4-L 10-1-B 9-4-L
Xylene (Deep (L. orange 9-3-K - (L. orange 9-2-K (Very dim + 9-9-I I(L. orange 9-3-K
o______range) yellow) (Yellow) yellow) (Yellow) yellow) (Orange) yellow) (Yellow)
9-9-L 9-4-L 9-4-L 10-1-B 9-4-L
Toluene ( (Deep (L. orange 9-3-K +-- (L. orange 9-2-L (Very dim + 9-9-1 j(L. orange 9-2-J e
+ orange) yellow) (Ylo yellow) yel ) (Yellow) I yellow) __ (Orange)I yellow (Yellow)
S9-9-L ~9-6-I 9-4-L 9-4-K 9-2-B 9-5-E
Carbon + (Deep 9-8-I (Light +- (L. range (Lorarange (Very dim + 9-9-I 9-8- (Pale
Disulfide orange) (Orange) orange) yellow) yellow) orange) (Orange) (Orange) I orange)
'Group I dissolves out all pigments equally.
II dissolves out carotin and traces of others.
III acts intermediately between first and second groups.
2Maerz and Paul Number.
CO
CO





Florida Agricultural Experiment Station


penetrate from all sides, making the conditions comparable to
liquid in a bottle. When the color was in solution it was not
practicable to use this method, and color comparisons were made
by examination of the liquid in the tumbler from the side without
a mask. In reporting the color reactions the general range of
color change is indicated in parentheses below the common
names.
Nature of Juice Sac Plastid Pigments.-The solubility tests
carried out gave results in harmony with the earlier work of
Matlack (24) on the nature of the plastid pigments in citrus
fruits (26). The data covering the solubility tests with the
usual carotinoid solvents are presented in Table X. The results
concerning the solubility tests for anthocyanins are indicated in
Table XI.
The data contained in Table X, based on juice sac material
from Owari Satsuma orange, Hamlin sweet orange and Dancy
Tangerine with the usual carotinoid solvents, show that the
pigments contained in this material are markedly soluble
in ethyl alcohol, acetone, acetaldehyde and chloroform, the
solvents which, according to Tswett (38), dissolve out all the
carotinoids equally. The solubility with petrol ether is as a
rule slightly less or nil. According to Tswett, petrol ether
dissolves out mainly carotin. The third group of solvents tried
consisted of those acting in an intermediate manner between the
foregoing (38)-benzene, xylene, toluene, and carbon disulfide.
These tests as a rule showed marked solubility except in the case
of sweet orange. In the case of the sweet orange the juice was
very light in color, owing to the comparative immaturity of the
fruit; with riper fruit a more definite reaction probably would be
obtained with these solvents.
The solubility tests with the usual technique used for antho-
cyanins (27) show that the juice sac pigments of Owari Sat-
suma orange, Hamlin sweet orange, Dancy tangerine, and Key
lime were insoluble in hot water, indicating that anthocyanins
are apparently absent.
Color Changes Due to Citrus Oil and Other Compounds.-As
indicated in Table I earlier in this report, the possible effect of
citrus oil brought in when juices are prepared by Method No. 2
was to change the original Satsuma orange color of the juice to
yellow. This opened up the field of color changes in prepared
juices. Since no very marked color changes were observed in






Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 35

TABLE XI.-SOLUBILITY OF FRESH PLASTID PIGMENTS OF VARIOUS CITRUS
TYPES IN HOT WATER.


Solubility in 50 cc.
solvent


SSolubility of
Lighter colored
Solubility of pigment resulting
original pigment in juice sac
in 100 gms. empty tissue to which
juice sacs peel oil has been
added


Original color of sacs 9-9-L 9-4-L (L.
olor of sa e (Deep orange) orange yellow)
Color of sacs after 9-9-L 9-4-L (L.
treatment (Deep orange) orange yellow)

Color of filtrate Colorless Colorless
Solubility in 50 cc.
solvent -
Original color of sacs 9-4-L (L. I 9-1-L
Orange yellow) (Yellow)
Color of sacs after 9-4-L (L. 9-1-L
treatment orange yellow) (Yellow)

SColor of filtrate Colorless Colorless
Solubility in 50 cc.
solvent_ -


Original color of sacs 9-9-I
I (Orange)
Color of sacs after 9-9-I
treatment (Orange)

Color of filtrate Colorless
Solubility in 50 cc.
solvent
Original color in sacs 17-2-G
(Green)
Color of sacs after 17-2-G
treatment (Green)

Color of filtrate Colorless


9-5-L
(Orange yellow)
9-5-L
(Orange yellow)

Colorless

i -
S17-1-J
(L. Yellow)
17-1-J
(Yellow)

S Colorless


(-) indicates the absence of any particular pigment.


the case of Methods 1, 3 and 4, it seemed logical to look for the
cause of the color change in the outer peel which introduced the
chief variation in Method 2. It was noticed also that the original
Satsuma orange color was changed to yellow as a result of
neutralization and pasteurization of the juice mixture. The
results of a typical experiment covering the effect of citrus oil,
neutralization and pasteurization on color changes in Owari
Satsuma orange, Hamlin sweet orange, Dancy tangerine, Key
lime and McCarty grapefruit are presented in Table XII. It


Type of
citrus fruit


Satsuma
(Owari)


Orange
(Hamlin)





Tangerine
(Dancy)


Lime
(Key)












TABLE XII.--COLOR CHANGES IN CITRUS FRUIT JUICES PRODUCED BY CITRUS OIL, ALKALI AND PASTUERIZATION.


Origina


Type of
citrus
fruit


Satsuma
Orange
(Owari)

Sweet
Orange
(Hamlin)

Tangerine
(Dancy)


Key Lime



Grapefruit
(McCarty)


laerz &
Paul
Number


9-7-L



9-2-I



9-6-K


17-2-G



10-1-D


1 color


Common
Name


Deep
chrome
(orange)

Pinard
(L. orange
yellow)

Golden
glow
(orange)


Sea foam
(yellow
green)

Marguerite
(pale
yellow)


After addition
distilled citru
to 25 cc.
Maerz &
Paul
Number

9-1-L



9-1-L



9-11/-L


17-1-J



10-1-F


L


n of 2 cc.
is peel oil
juice

Common
Name


Sulfur
(yellow)


Sulfur
(yellow)


Sulfur
(yellow)


Martius
(light
yellow)

ight straw
(light
yellow)


After neutralization
with .1 N NaOH

Maerz & Common
Paul Name
Number


After pasteurization
180 F. for 30 minutes

Maerz & Common
Paul name
Number


9-2-K Chrome 9-4-L
lemon
(yellow)

11-1-K Acacia 9-1-J
(Dull green
yellow)

9-3-K Empire 9-4-K
(yellow)


Light 17-1-J
17-1%-K Citronelle
I(yellow green)l I
Acacia
11-1-K (dull green 10-1-F
yellow)


Sunflower
(yellow)


Deep
Martius
(yellow)

Jasmine
(yellow)


Martius
(Light
yellow)

Light straw
(light
yellow)


M
N


I


I


i


I


v o





Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 37

will be noted that the original color of prepared juices, orange
or yellow as the case may be, can be readily changed from orange
to a lighter shade of orange, or to yellow; or from yellow to a
lighter shade of yellow, by the three methods indicated. In the
case of neutralization the color change is reversible within cer-
tain limits.
Apparently the source of the citrus peel oil, as shown in Table
XIII, does not affect the results, since the change takes place
in all citrus groups studied, whether sweet orange, Satsuma
orange, tangerine, grapefruit or lime oil is used. It should be
noted also that hand-pressed oil gives the same results as dis-
tilled oil. In the case of the sap expressed from sweet orange
peel from which the oil has been extracted as shown in Table
XIII, no characteristic change of color was observed in Satsuma,
tangerine and sweet orange juices. This would indicate that
the causal agent is present in the citrus oil and not in the rest
of the outer peel tissue.
The data in Table XIII show also that the degree of observed
color change is, within the limits shown (1, 2, and 10 parts per
1,000 parts of juice), in a marked degree proportional to the
amount of citrus oil added. The figures show also that, within
these limits, the rate of color change is in a marked degree pro-
portional to the amount of oil added.
The experiment was carried a step further in a preliminary
attempt to determine the factors involved. The following groups
of oils and resins, and glycerine were added to citrus juice
pressed from juice sacs only (Satsuma, tangerine and sweet
orange): (a) essential oils-orange oil (check treatment), clove
oil, cedar oil, citronella oil, turpentine; (b) resin-Canada balsam;
(c) fruit and vegetable oil-avocado oil, pecan oil, castor oil
and linseed oil; (d) cod-liver oil, and (e) alcholoic constituent
of non-volatile fats and oils-glycerol. The results were quite
consistent in showing that the essential oils and resins have a
similar effect in changing the color of citrus juice mixtures, as
has the check treatment with orange oil which is also of the
same group. The fruit and vegetable oils, cod-liver oil, and
glycerol, had no effect in changing color except very slightly in
the.case of Satsuma orange juice mixture.
In Table XIV preliminary data are presented showing some
changes in color of prepared citrus juices due to method of
extraction and after-treatment as represented by freezing and
cool storage. The characteristic color changes due to small





TABLE XIII.-THE EFFECT OF VARYING AMOUNTS OF CITRUS PEEL OIL ON COLOR CHANGES IN CITRUS JUICES.


Satsuma (Owari) juice Tangerine (Dancy) juice
(a d to 2 Original color Observed color Original color- Obs
juice from Maerz & I Time I Maerz & I Time Maerz &
juice acs oly) Paul CommonName Inerval Maer & Paul Commonname Paul Common Interval Paul
Number lI hrs. I Number Number name hrs. Number
1/4 I 9-7-L 1/4 9-6-K
No treatment 9-7-L Deep chrome 1/2 9-7 L Deep chrome 9-6-K Forsythia 1/2 9-6-K
(check) (orange) 3 9-7-L --- (orange) (orange) 3 9-6-K --
Distilled I 1/4 9-6-L 1/4 9-5-K
orange oil 9-7-L Deep chrome 1/2 9-4-L Chrome lemon 9-6-K Forsythia 1/2 9-4-K
0.025 cc. (orange) 3 9-2-L - (yellow) (orange) 3 9-2-L--
Distilled 1/4 9-4-L 1/4 9-4-K
orange oil 9-7-L Deep chrome 1/2 9-3-L Chrome lemon 9-6-K Forsythia 1/2 9-3-KL%
0.05 cc. (orange) 3 9-1%-L-- I (yellow) (orange) 3 9-2-L -
Distilled 1/4 9-2-L 1/4 9-2-L
orange oil 9-7-L Deep chrome 1/2 9-1-L Deep sulphur 9-6-K Forsythia 1/2 9-2-L
0.25 cc. (orange) 3 9-1-L---- (yellow) (orange) 3 9-1-I--
Distilled 1/4 9-6-L 1/4 9-5-K
tangerine oil 9-7-L Deep chrome 1/2 9-4-L Chrome lemon 9-6-K Forsythia 1/2 9-4-K
0.025 cc. (orange) 3 9-2-L----- (yellow) (orange) 3 9-2-L--
Distilled 1/4 9-4-L 1/4 9-4-K3
tangerine oil 9-7-L Deep chrome 1/2 9-2%-L Chrome lemon 9-6-K Forsythia 1/2 9-3-K%2
0.05 cc. (orange) 3 9-1%-L--- (yellow) (orange) 3 9-2-L --
Distilled 1/4 9-2-L 1/4 9-3-L
tangerine oil 9-7-L Deep chrome 1/2 9-1-L Deep sulphur 9-6-K Forsythia 1/2 9-2-L
0.25 cc. (orange) 3 9-1-L---- (yellow) (orange) 3 9-1-L--
Distilled 1/4 9-6-L F 1/4 9-5-K
grapefruit oil 9-7-L Deep chrome 1/2 9-4-L Chrome lemon 9-6-K Forsythia 1/2 9-3-K
0.025 cc. (orange) 3 9-2-L -- (yellow) (orange) 3 9-2-L--
Distilled i 14 9-3-L I 1/4 9-4-K
grapefruit oil 9-7-L Deep chrome 1/2 9-2-L j Chrome lemon 9-6-K Forsythia 1/2 9--L
0.05 cc. (orange) 3 9-1 -L --- (yellow) (orange) 3 9-2-L --
Distilled F 1/4 9-2-L 1/4 9-3-L
grapefruit oil 9-7-L I Deep chrome 1/2 9-1-L Deep sulphur 9-6-K Forsythia 1/2 9-2-L
0.25 cc. F (orange) 3 9-1-L- - (yellow) (orange) 3 9-1-L-
Hand pressed 1/4 9-2-L 1/4 9-3-K
sweet orange 9-7-L Deep chrome 1/2 9-1-L Deep sulphur 9-6-K Forsythia 1/2 9-3-K
oil 0.25 cc. (orange) 3 9-1-L------- (yellow) (orange) 3 9-2-J --
Hand pressed F 1/4 9-2-L 1/4 9-3/-L
Satsuma oil 9-7-L I Deep chrome 1/2 9-1-L Deep sulphur 9-6-K Forsythia 1/2 9-L
0.25 cc. (orange) 3 9-1-L --- (yellow) (orange) 3 9-2-L -


Hand pressed 1/4 9-3-L I1/4 9-3-L
tangerine oil 9-7-L I Deep chrome 1/2 9-2-L Deep sulphur 9-6-K Forsythia 1/2 9-3-L Chrome lemon
0.25 cc. I (orange) 3 9-1-L- ---- (yellow) F (orange) 3 9-2-L -- (yellow)
Hand pressed I 1/4 9-3-L 1/4 9-3-L
lime oil 9-7-L 1 Deep chrome 1/2 9-2-L Deep sulphur 9-6-K Forsythia 1/2 9-3-L Chrome lemon
0.25 cc. I (orange) 9-1-L (yellow) (orange) 3 9-2-L-- (yellow)
Orange peel F 1/4 y-'--Li I 1/4 9-6-K
sap less oil 9-7-L Deep chrome 1/2 9-7-L Deep chrome 9-6-K Forsythia 1/2 9-6-K Forsythia
1 cc. I (orange) 3 9-7-L -- (orange) 1 (orange) 3 9-6-K-- (orange)


served color

Common name


Forsythia
(orange)

Chrome lemon
(yellow)

Chrome lemon
(yellow)

Deep sulphur
(yellow)

Chrome lemon
S (yellow)

Chrome lemon
(yellow)

Deep sulphur
(yellow)

Chrome lemon
(yellow)

Chrome lemon
(yellow)

Deep sulphur
(yellow)

Chrome lemon
(yellow)

SChrome lemon
S 'yellow)






Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 39

TABLE XIII. THE EFFECT OF VARYING AMOUNTS OF CITRUS PEEL OIL
ON COLOR CHANGES IN CITRUS JUICEs.-Continued.

Treatment O Sweet orange (Hamlin) juice
(added to 25 cc. Original color | Observed color
juice from lMaerz & Time Maerz &
juice sacs only) Paul Common interv'l Paul Common
Number name hrs. Number name
Pinard 1/4 9-2-I Pinard
No treatment 9-2-I (light orange 1/2 9-2-I (light orange
(check) yellow) 3 9-2-1- yellow)
Distilled Pinard 1/4 9-1-J
orange oil 9-2-I (light orange 1/2 9-1-K Sulphur
0.025 cc. yellow) 3 9-1-K (yellow)
Distilled Pinard 1/4 9-1-J%/
orange oil 9-2-I (light orange 1/2 9-1-K Sulphur
0.05 cc. yellow) 3 9-1-K% (yellow)
Distilled Pinard 1/4 9-1-K
orange oil 9-2-I (light orange 1/2 9-1-K% Deep sulphur
0.25 cc. yellow) 3 9-1-L (yellow)
Distilled Pinard 1/4 9-1-J
tangerine oil 9-2-I (light orange 1/2 9-1-J% Sulphur
0.025 cc. yellow) 3 9-1-K (yellow)
Distilled Pinard 1/4 9-1-J
tangerine oil 9-2-I (light orange 1/2 9-1-K Sulphur
0.05 cc. yellow) 3 9-1-K (yellow)
,Distilled Pinard 1/4 9-1-K
tangerine oil 9-2-I (light orange 1/2 9-1-K% Deep sulphur
0.25 cc. yellow) 3 9-1-L (yellow)
Distilled Pinard 1/4 9-1-J
grapefruit oil 9-2-I (light orange 1/2 9-1-J% Sulphur
0.025 ce. yellow) 3 9-1-K (yellow)
Distilled Pinard 1/4 9-1-J%
grapefruit oil 9-2-I (light orange 1/2 9-1-K Sulphur
0.05 cc. yellow) 3 9-1-K/2 (yellow)
Distilled Pinard 1/4 9-1-K
grapefruit oil 9-2-I (light orange 1/2 9-1-L Deep sulphur
0.25 cc. __yellow) 3 9-1-L (yellow)
Hand pressed Pinard 1/4 9-1-K%
sweet orange 9-2-I (light orange 1/2 9-1-L Deep sulphur
oil 0.25 cc. yellow) 3 9-1-L (yellow)
Hand pressed Pinard 1/4 9-1-K%/
Satsuma oil 9-2-I (light orange 1/2 9-1-L Deep sulphur
0.25 cc. yellow) 3 9-1-L (yellow)
Hand pressed Pinard 1/4 9-1-KY
tangerine oil 9-2-I (light orange 1/2 9-1-L Deep sulphur
0.25 cc. yellow) 3 9-1-L (yellow)
Hand pressed Pinard 1/4 9-1-K
lime oil 9-2-I (light orange 1/2 9-1-L Deep sulphur
0.25 cc. yellow) 3 9-1-L---- (yellow)
Orange peel Pinard 1/4 9-2-I Pinard
sap less oil 9-2-I (light orange 1/2 9-2-I (light orange
1 cc. yellow) 3 9-2-I- yellow)


amounts of citrus oil present in the citrus juice mixture have
been discussed. The data presented in Table XIV are concerned
primarily with the effect of freezing and cold storage on the
color of the prepared product. In general it should be noted
that there is a slight change in color tone due to these treat-
ments. The data recorded show that the change is from orange
with a medium yellow tone to the same color with a lighter
yellow tone. In only a few exceptional cases is there a change
in the opposite direction, or changes from darker or lighter
shades of the same color or vice versa, simultaneous with a
change in tone value (see discussion in Maerz and Paul (22)).



















TABLE XIV.-EFFECT OF METHOD OF EXTRACTION AND TREATMENT ON COLOR CHANGES IN CITRUS JUICES.


Variety



Sweet orange (Hamlin)










Sweet orange (Pineapple)


Date


11/20/31










11/23/31


Method of After treatment
preparation


1 Original juice
1 Frozen
2 Original juice
2 Cold stored
2 Frozen
3 Original juice
3 Cold stored
3 Frozen
4 Original juice
4 Cold stored
4 Frozen

1 Original juice
2 Original juice
2 Cold stored
2 Frozen
3 Original juice
3 Cold stored
3 Frozen
4 Orioinal juice
4 Cold stored
4 Frozen


Storage
period
(days)


2
2

2
2

2
2


Color
Maerz and
Paul Common name
number

9-1-J Bright Martius (yellow)
9-1-I Martius (yellow)
9-2-L Chrome lemon (yellow)
9-1-K Light sulphur (yellow)
9-1-L Sulphur (yellow)
9-3-L Bright Empire (yellow)
9-1-K Light sulphur (yellow)
9-11/2-L Sulphur (yellow)
9-4-L Sunflower (yellow)
9-1/2-L Sulphur (yellow)
9-1'A-L Sulphur (yellow)


9-1Y2-J
9-12-L
9-112-L
9-2-L
9-1%-L
9-12-L
9-2-L
9-11/-L
9-11/2-L


Pinard (yellow)
Chrome lemon (yellow)
Sulphur (yellow)
Sulphur (yellow)
Chrome lemon (yellow)
Sulphur (yellow)
Sulphur (yellow)
Chrome lemon (yellow)
Sulphur (yellow)
Sulphur (yellow)





I


,











TABLE XIV.-EFFECT OF METHOD OF EXTRACTION AND TREATMENT ON COLOR CHANGES IN CITRUS JUICES.-Continued.


Storage _Color
Variety Date Method of After treatment period Maerz and
preparation (days) Paul Common name
Number
Satsuma (Owari) 11/19/31 1 Original juice 9-8-L Cadmium (deep orange)
S1 Frozen 6 9-6%-L Golden Glow (orange)
"2 Original juice 9-9-L Sunkiss (deep orange)
"2 Cold stored 1 9-8/%-L Cadmium (deep orange)
S2 Cold stored 4 9-8%-L Cadmium (deep orange)
2 Cold stored 6 9-8-L Cadmium (deep orange)
2 Frozen 6 9-8-L Cadmium (deep orange)
Original juice 9-10-K Marigold (deep orange)
"3 Cold stored 1 9-9-L Sunkiss (deep orange)
3 Cold stored 4 9-82-L Cadmium (deep orange)
Cold stored 6 9-8-L Cadmium (deep orange)
3 Frozen 6 9-8-L Cadmium (deep orange)
4 Original juice 9-10-L Marigold (deep orange)
4 Cold stored 1 9-9-L Sunkiss (deep orange)
4 Cold stored 4 9-8-L Cadmium (deep orange)
S 4 Cold stored 6 9-8-L Cadmium (deep orange)
4 Frozen 6 9-8-L Cadmium (deep orange)

Tangerine (Dancy) 11/23/31 1 Original juice 11-3-E Light Maple (dull orange yellow)
S" 2 Original juice 9-7-L Deep chrome (orange)
2 Cold stored 4 9-6/-K Forsythia (orange)
"2 Frozen 4 9-71%-L Deep chrome (orange)
"3 Original juice 9-8-L Cadmium (deep orange)
Cold stored 4 9-8-K Capucine (deep orange)
Frozen 4 9-7%-L Deep chrome (orange)
"4 Original juice 9-8-L Cadmium (deep orange)
4 Cold stored 4 9-8-K Capucine (deep orange)
4 Frozen I 4 9-7-L Deep chrome (oronee)





Florida Agricultural Experiment Station


In considering the application of these results it should be
realized that in the case of citrus juices which are naturally of
a deep Satsuma, tangerine or orange color, any changes to lighter
shades of the same color, or to a yellow color, would be a distinct
drawback. However, in the case of dull shades of yellow, a
change to a brighter yellow may constitute an improvement.
The subject of the relative amounts of citrus oil required to
obtain a given color effect is of importance not only to those
choosing a method of preparation already available but also to
those interested in the design of improved machinery for juice
preparation.
As indicated at the beginning of this section, the color factor
is secondary to that of taste, and the amount of citrus oil used
must in every case be considered from the standpoint of agree-
ableness in taste of the product.

CHANGES IN DIRECTION AND RATE OF MOVEMENT
OF SUSPENDED PARTICLES
Extracted citrus juices are made up of two distinct phases:
one is a liquid phase which is almost transparent and contains
mainly dissolved substances such as sugars and acids and some
colloidal material, and the other is a solid phase consisting of
small particles of juice sac, locular wall, inner peel or other
tissues, in suspension in the liquid phase. The particles in sus-
pension carry the pigment which gives the juice its color and
are closely associated with the characteristic taste of orange
juice. Clarified juices do not have this characteristic taste and
cannot be substituted for the freshly extracted juice. The larger
solid particles begin separating from the liquid phase immedi-
ately after extraction. If the juice is allowed to stand long
enough undisturbed, there will result an almost purely liquid
zone, which is water clear, and a second zone, or zones, consisting
of a minimum of liquid and most of the solid particles. In juices
prepared by the usual methods the separation as above indicated
will finally take place, but the methods of preparation and other
factors have a pronounced effect upon the rate at which it takes
place. Other things being equal, the juice that shows the slowest
rate of separation is most desirable.
In determining the direction and rate of movement of particles
in the juice mixture the samples were shaken up and poured into
100 cc. graduates, and records of amount and direction of move-





Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 43

ment as well as regional differences in turbidity were taken at
15-minute intervals during the first hour and at greater intervals
for the next 20 hours, and recorded as volume of a region or
zone.
Only relative differences in turbidity are indicated in the
present report. A more accurate method on the basis of nephel-
ometer readings (19, 20) is at present under consideration. Ac-
cording to the method used, the turbidity of the sample was ob-
served in the 100 cc. graduated cylinder. The readings were
taken primarily on the less turbid upper portion or on the cen-
tral portion when some of the suspended particles had risen.
The symbols used and their relative values are more or less
arbitrary: thus (+ ++ +) represented a condition where
the liquid was practically opaque. Increasing degrees of trans-
lucency are represented by (+ + +), (+ +), (+), and
(+ -). When the liquid becomes almost transparent, so that
outlines may be seen through the cylinder, the condition is
represented by (+ -). Increasing degrees of transparency
are indicated by (+ - -), etc.
The prepared citrus juice mixture as indicated in the previous
discussion, is a buffered biological solution containing in ad-
dition extracted solutes and suspended particles derived from
the tissues of the fruit during the process of preparation. Ap-
parently the method of preparation should have a profound
effect upon the total amount of mass in suspension, the direction
and rate of its movement, and also the relative turbidity of the
liquid mixture. Such factors as the stage of maturity of the
fruit and the effect of various subsequent treatments of the
juice, such as the effect of containers, gases in contact with
juice, freezing, storage temperature, and length of storage per-
iod, are also of importance in this connection.
The exact role of the various component parts as they affect
the stability of the citrus juice mixture has not been definitely
determined. The constituents possibly affecting the character of
the juice mixture may be divided into two classes: (a) sub-
stances in true solution, such as sugars, citric acid, proteins and
pectins; (b) substances present in the colloidal state, such as
proteins and pectins; (c) matter in mass, composed of larger
suspended particles.
The first step in the attempt to understand the stability of
the suspension was to study the behavior of infusions of the
tissues of the fruit in the concentrated condition and also diluted





Florida Agricultural Experiment Station


with juice extracted from juice sacs only and with water. The
following tissues were considered: outer peel, inner peel and
veins, locular walls, central axis, seed coat, and cotyledon and
germ. Of the tissues tested, apparently the locular wall and
inner peel and veins infusions gave the most turbid and stable
mixtures. The germ and cotyledon infusions also gave turbid and
stable infusions. When tissue infusions were diluted in the pro-
portions, 2, 4 and 8 parts of infusion to 100 parts of juice from
juice sacs only or with water, the results were identical with
those indicated above, showing that even small amounts of these
tissue infusions will have a marked effect on the stability of the
suspension as measured by the relative turbidity.
As previously indicated, the turbidity and color of the juice
mixture is due to particles of tissue introduced by the method
of extraction, and these tend to separate out from the liquid
phase. The direction and rate of movement may be affected by
the size and specific gravity of the particles, by the possible
presence or absence of stabilizing substances such as oils, pec-
tins and proteins or precipitants (electrolytic or colloidal), and
by indirect effects such as might be produced by enzymes. A
preliminary report will be given here on the effect of the size
of the particles, of citrus oil, and of cool storage and freezing.
Other phases of the subject are being studied and the entire
field will be reported upon more in detail in a future publication.
The effect of decreasing the size of particles on the stability
of the suspension was studied by using a ball mill and a colloid
mill to reduce the size of the particles. In general, the stability
of the suspension increases with decrease in size of particles,
as indicated by the number of hours the material was ground
in a ball mill (Table XV), while the color intensity decreases
with decrease in size of particles. It will be noted also that the
turbidity of the translucent portion is directly correlated with
the increase of stability as indicated by (+ -) turbidity at
the end of three hours for Dancy tangerines in untreated ma-
terial and (+ +) for a similar sample ground in the ball mill for
two hours. A second experiment was carried out with juices
run through a colloid mill. The results to some extent parallel
those secured by the use of the ball mill, though the colloid mill
was not as effective in this regard as the ball mill. As was to
be expected, the color of the juice mixture changed to a lighter
shade with decrease in size of the particles. The results obtained
by the use of a high speed soda fountain stirrer were very





TABLE XV.-THE EFFECT ON THE STABILITY OF THE CITRUS JUICE SUSPENSION OF DECREASING SIZE OF PARTICLES
BY BALL MILL GRINDING.


*No reading.
'Volumes read in 100 cc. cylinders.
2In grinding a liquid in a ball mill some sandy or powdery rock material is produced. When juice ground in this way
is set up in cylinders a heavy precipitate, chiefly composed of ground-up rock, comes down quickly and is followed later by
settling that are derived from material in the juice; these zones are separately reported here. The sand zone contained a
small proportion of citrus tissue.





Florida Agricultural Experiment Station


good, giving a more stable suspension than was obtained by use
of the colloid mill.
As has been pointed out earlier in this publication, the juices
studied in these experiments were all subjected to vacuum treat-
ment to remove the variable factor (amount of dissolved gases)
that would have been brought in if the material had not been
treated in this manner. In general when expressed untreated
citrus juices are allowed to stand at room temperature after
thorough shaking, three zones are formed. A small portion of
the particles moves upward and a larger portion settles at the
bottom, leaving a more or less translucent region between them
(Table XVI). When juices are vacuumized, however, the ten-
dency is for the particles to move downward leaving a more or
less translucent upper region (Table XVI).
The rates of settling during the first few hours, for juices
prepared by Methods Nos. 1 and 2 as a rule were similar to the
rate for juice prepared by Method 4, this being the slowest. In
the case of Method 1, a few larger particles settle out quickly
but the turbidity of the remainder of the juice is so great as
to mask this. When the turbidity is greatly reduced for some
reason, this layer of coarse particles becomes apparent and the
rate of settling would be indicated as very rapid if this were
taken as the indication of settling. The rate of settling for
juices prepared by Method No. 3 is much more rapid than for
Methods Nos. 1, 2 and 4. For Method No. 2 there is little or
no settling during the first hour or so after standing. For
Method No. 3, there is rapid settling during the same period and
in the case of Method No. 4 the tendency is again similar to that
for Method No. 2. After standing for more than two or three
hours the rate of settling for Methods No. 2 and 4 apparently
proceeds at a rate similar to that of Method No. 3 and after 20
hours the amount of settling is approximately the same for
Methods Nos. 2 and 3, but for Method No. 4 the absolute value
is higher within the period indicated.
After the juices prepared by the four methods were put in
glass containers and vacuumized, further treatments were em-
ployed-cool storage at 320F. (0C.) and freezing at -20 to
-25 degrees F. (-28 to -31 degrees C.) with storage in the
frozen condition at 0F. Some of the experimental results con-
cerning the possible effect of the two methods of storage on the
stability of the juice mixture are summarized in Tables XVII
and XVIII.











TABLE XVI.-EFFECT OF VACUUMIZATION ON STABILITY OF THE CITRUS JUICE SUSPENSION.

1Method IVolume in cc.' of zone or zones containing separated solids
Variety and Date of Ater I after varying periods of time (in hours)
source prepared prepa- treatment Zone
ration_ I % 1 I 2 3 1 4 ( 5 | 6 ( 8 24
Dancy Top 20 18 16 14 18 8
Tangerine 11/24/31 2 Untreated Bottom 7 6 20 20 20 17
(Bartow) Turbidity' + ---
Dancy Top 57 46 39 5 29
Tangerine 11/24/31 2 Bottom 0 0 8 11
(Hawthorne) Turbidity -- -- ---
STop 0
2 Juice Bottom 97 80 58 5 52 38
vacuumizedl Turbidity +- +- +- *
-Top 0
," 2 Bottom 95 92 26 54
I Turbidity +* *
*No observations made.
'Volumes read in 100 cc. cylinders.





TABLE XVII.-EFFECT OF METHOD OF EXTRACTION AND AFTER TREATMENT ON THE STABILITY OF THE
CITRUS JUICE SUSPENSION.


Type o frui


Type of fruit
and variety


Orange (Hamlin)
it


Satsuma (Owari)
14


Date
prepared


11/20




it

"


After
treatment


Method
of
prepa-
ration

1


.2
It


3



it
it


"
"


*No readings made.
1Volumes read in 100 cc. cylinder.


Storage
period
(days)


5


3
5


3
5


3
5


Volume in cc.1 of more turbid region and turbidities of less
turbid region after varying periods of time (hrs.)


Original juice
Frozen

Original juice
Cold stored
Frozen

Original juice
Cold stored
Frozen

Original juice
Cold stored
Frozen

Original juice
Frozen

Original juice
Cold stored




Frozen

Original juice
Cold stored
it
"


*
6
++

78
94
+
*
90
55
+
97
97
95

*
6
++
*

90

91
++
88
+
*
*
73
71
++


8
5
+

56
72
+--
53
67
40
+--
*
94
85
+
*
6
++
*
60
70
++
70
+
63
+
*
52
55
54
+


4

*
5
+
48
52
63
+2-
63
39
+-
*
92
81
+
8
6
++
*
*
65
+++
65
+-
60
+
*
*
51
52
+-


98
*

12
*

97
*
95

93



85
*
86
80


11/19
t'

it
"




TABLE XVII.-EFFECT OF METHOD OF EXTRACTION AND AFTER TREATMENT ON THE STABILITY OF THE
CITRUS JUICE SUSPENSION.-Continued.


Type of fruit
and variety


Satsuma (Owari)
(continued)



it

it

Tangerine (Dancy)










it



Lime (Tahiti)
it


Date
prepared


11/19


"t


11/23
44
it

it

it
it
"

f
"t
It





7/22
"


Methcd
of
prepa-
ration

3

4
it
"t


After
treatment


Frozen

Original juice
Cold stored

Frozen

Frozen


Storage
period
(days)

6


1
4

6

6


Original juice

Cold stored 4

Frozen 4

Original juice
Cold stored 4

Frozen 4

Original juice
Cold stored 4

Frozen 4

Frozen | 4 months
"


Volume in cc.1 of more turbid region and turbidities of less
turbid region after varying periods of time (hrs.)


Y4 V2

63
+"2
* 93
98 *
98 96

90


72
+


100
94
*


100

94
+


100
100
94
+
*
100

100

37
++
40
+++


*

95

98
+
84
+--

98
+
84
+-
*
99
+
97
+-
30
++
34
++


% I 1 2

46 39
+ +
75 63
83
94 91 88
++
86 83 80
++ ++ ++
59 '* 46
+ +


97
99
+-
*

21
2--

++
25
++


3 4

32 30
+ +
*
62 *
83 78
+++ +++
70 66
++ ++
42 39
+ +


*
*
*

46
+--
92
*

46
+--
94
95
+--
*

20 ]
++
23
++


27
63
89 51
+- +--
29
+--
61
72 45
+ +--
29
+--
80
70
+---
59
+-
19 ] 15
++ ++
23 15
++ ++


"No readings made.
'Volumes read in 100 cc. cylinder.
'Turbidity of less turbid region are shown immediately under volume of more turbid region.
















TABLE XVIII.-EFFECT OF RATE OF FREEZING ON THE STABILITY OF THE CITRUS JUICE SUSPENSION
(VALENCIA SWEET ORANGE).


Variety


Sweet orange
(Valencia)
44


Method
Date of
prepared prepa-
ration


7/24/31
"


After
treat-
ment

Frozen

"


Time Volume in cc.' of zone or zones containing separated solids
Storage required after varying periods of time (hrs.) and turbidity of
period for supernatant liquid
freezing 1 j 2 3 4 6 8 24

4 mos. 25 min. 100 33 27 21 20 19 17 15 15
I++ +++ + + + + + + +
30 min. 62 48 38 30 27 25 24 22 20
++++ + + + + + + +
90 min. 100 44 32 25 23 21 20 20 18
++ ++ + + + + + + +
110 min. 80 68 53 39. 34 31 28 25 23
++ +++ + + + + +
10 hrs. 60 44 35 27 25 24 21 21 20
++ ++ + + + + + + +
12 hrs. 65 49 38 29 27 25 22 22 20
++ ++ + + + + + + +


'Volumes read in 100 cc. cylinder.







TABLE XIX.-THE EFFECT OF PRESENCE OF CITRUS OIL ON THE STABILITY OF THE CITRUS JUICE SUSPENSION.

Date Method of After Volume of separated zone in cc. and turbidity after
Variety prepared preparation treatment Zone varying periods of time (in hours)
4 1/ 21 ______ 3 2 | 6 9 11 24
Orange 12/16/31 2 Untreated Bottom 095 84 60 50 45 43 35
(Hamlin) (Vacuumized) Top +--- +-- +--- +--- +- ---
SBottom +++ +++ +++ +++ +++ +++
1% citrus Top' 90 Breaking 17 15 15 15 10
Ioil added Center' Curdy 45 40 40 35 34'
Bottom' 10 10 10 10 10
Translucent2 ,--- +-- +-- - 5__+--_-_- +---
Separated2 . 5. 5 ++ +++ +++ +++ +++
Tangerine Untreated Bottom 0 85 43 32 29 25 22
(Dancy) Top +- +- +- +- +-
Bottom +++ +++ +++ +++ +++
S1% citrus Top' 0 Curds 35 30 30 30 20
oil added Bottom' 10 12 12 12 10
Top ++++ ++++++++++ ++ ++++
Center ++ + + + +--
Bottom .+++ +++ +++ +++ +++5 +

*No readings taken.
'When oil was added to orange juice all of the solids started to rise and then became curdy and separated out to form
an upper, a central and a bottom layer with two zones of translucent liquid separating them; the volume rather than the
exact position of the central zone is shown.
2Since the two translucent zones appeared identical and the turbidity of the zones containing separated solids also
appeared identical, the turbidities are given under these two headings.






Florida Agricultural Experiment Station


In Table XVIII data are presented showing that after four
months of storage (juice prepared by Method No. 2 and the rate
of freezing varying from 25 minutes to 12 hours) the treatment
gave the following results: In the case of the slower rates of
freezing, 10 and 12 hours, the settling was, in general, more
rapid than in quicker rates, 25 to 110 minutes.
The data presented in Table XVII concerning the effect on
the rate of settling when juices prepared by the four methods
are stored at 320F. or in the frozen condition at 0F. show that
the rate of settling is not markedly affected by these after-
treatments.
In certain methods of manufacture, citrus oil is introduced
into the juice. An experiment was carried out to determine the
effect of citrus oil on the relative stability of the suspension.
When a small amount of citrus oil was added to the citrus juice
mixture, a portion of the particles rose to the top, as shown in
Table XIX. Other experiments show that when excessive
amounts of citrus oil were added, all of the larger suspended
particles in the juice mixture rose to the top.

SUMMARY
METHODS
The method of localizing in the tissues of the citrus fruit,
whenever possible, the cause or causes of undesirable qualities
in the prepared citrus juice mixture has yielded important
results.
CHANGES IN TASTE QUALITIES
The cause of the bitter taste developed in prepared citrus
juice on aging has been identified as of glucosidal origin and
has been localized primarily in the inner peel and veins and locu-
lar wall tissues, the degree of its development being a function
of fruit maturity, citrus type and variety, method of preparation,
and after-treatment.
The kind of bitter taste developed for the samples tested was
found to depend on the nature of the glucoside contained in the
particular type of citrus fruit.
The mechanism involved in the development of a bitter taste
in the prepared citrus juice mixture was found to be non-
enzymatic in nature.
The tendency of prepared citrus juices to develop a bitter
taste on aging was found to decrease with maturity of the fruit





Bul. 243, Factors Affecting Quality of Prepared Citrus Juices 53

used. This is in harmony with the known fact that the gluco-
side content of citrus fruits decreases with maturity.
Minimum amounts of citrus peel oil for the time periods cov-
ered by the experiments did not prove objectionable from the
standpoint of taste quality.
Undesirable taste qualities other than the distinctly bitter
taste were encountered under certain conditions. Certain ones of
these must be effectively controlled before a completely satisfac-
tory frozen or cold stored product can be secured.
CHANGES IN COLOR QUALITIES
The causal agent for the observed color changes in prepared
citrus juices has been traced to the outer peel and identified as
citrus oil. When citrus oil was added to the juice mixture the
orange or yellow color was changed from the original color to
brighter shades of the same color or to yellow, or from yellow
to lighter shades of yellow. Somewhat similar results were ob-
tained by neutralizing and by pasteurizing the juice mixture,
as well as by the addition of certain other essential oils and
resins.
Within the limits of the experiments the degree and the rate
of change in color were in a marked degree proportional to the
amount of citrus oil added.
STABILITY OF THE SUSPENSION
The stability of the suspension is being investigated on the
basis of the constituents brought into the juice mixture by the
method of manufacture.
Reducing the size of the suspended particles by grinding or
other treatments improved the stability of the suspension and
lightened the color of the product.
In prepared citrus juices a portion of the suspended particles
rose and another portion settled; following vacuumizatiofi all of
the suspended particles settled.
The method of preparation had a material effect upon th1
rate of movement of the suspended particles immediately after
thoroughly mixing the juice mixture but after two to four hours
standing the rates of movement of the particles were similar
for all methods of preparation used.
Preliminary experiments seemed to indicate that rates of
freezing had a greater effect upon the stability of the suspen-
sion than the type of storage. Quick freezing and cool storage






54 Florida Agricultural Experiment Sfttif ;o

of juice did not materially affect the rate of movement of the
suspended particles, as compared with freshly prepared juice.
The presence of small amounts of citrus oil caused a portion
of the particles to rise instead of settle and very large amounts
of oil caused all particles to rise.

LITERATURE CITED

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56 Flohril, Agricultural Experiment Station

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