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Title: pectic constituents of citrus fruits
Alternate Title: Bulletin 268 ; Florida Agricultural Experiment Station
Physical Description: Book
Language: English
Creator: Gaddum, L. W.
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville, Fla.
Publication Date: June, 1934
Copyright Date: 1934
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Bibliographic ID: UF00027096
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
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        Page 1
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    Main
        Page 3
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        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
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        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
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        Page 23
Full Text



Bulletin 268 June, 1934

UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA
Wilmon Newell, Director











THE PECTIC CONSTITUENTS

OF CITRUS FRUITS


By L. W. GADDUM









TECHNICAL BULLETIN







Bulletins will be sent free upon application to the
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


L










EXECUTIVE STAFF BOARD OF CONTROL
John J. Tigert, M.A., LL.D., President of the Geo. H. Baldwin, Chairman, Jacksonville
University A. H. Blanding, Bartow
Wilmon Newell, D.Sc., Director A. H. Wagg, West Palm Beach
H. Harold Hume, M.S., Asst. Dir., Research Oliver J. Semmes, Pensacola
Harold Mowry, B.S.A., Asst. Dir., Adm. Harry C. Duncan, Tavares
J. Francis Cooper, M.S.A., Editor J. T. Diamond, Secretary, Tallahassee
R. M. Fulghum, B.S.A., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager BRANCH STATIONS
K. H. Graham. Business Manager
Rachel McQuarrie, Accountant NORTH FLORIDA STATION, QUINCY
L. O. Gratz. Ph.D., Plant Pathologist in Charge
R. R. Kincaid, M.S., Asst. Plant Pathologist
J. D. Warner, M.S., Agronomist
MAIN STATION, GAINESVILLE M. Crown, B.S.A., Assistant Agronomist
Jesse Reeves, Farm Superintendent
AGRONOMY
W. E. Stokes, M.S., Agronomist** CITRUS STATION, LAKE ALFRED
W. A. Leukel, Ph.D., Agronomist John H. Jefferies. Superintendent
G. E. Ritchey, M.S.A., Associate* Geo. D. Ruehle, Ph.D., Associate Plant Pathol-
Fred H. Hull, M.S.. Associate ogist
W. A. Carver, Ph.D., Associate W. A. Kuntz, A.M., Associate Plant Pathologist
John P. Camp, M.S., Assistant B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Assistant Entomologist
ANIMAL HUSBANDRY EVERGLADES STATION, BELLE GLADE
A. L. Shealy, D.V.M., Animal Husbandman**
R. B. Becker, Ph.D., Dairy Husbandman A. Daane, Ph.D., Agronomist in Charge
W. M. Neal, Ph.D., Associate in Animal Nutri- R. N. Lobdell, M.S., Entomologist
tion F. D. Stevens, B.S., Sugarcane Agronomist
D. A. Sanders, D.V.M., Veterinarian G. R. Townsend, Ph.D., Asst. Plant Pathologist
M. W. Emmel, D.V.M., Assistant Veterinarian B. A. Bourne, Ph.D., Sugarcane Physiologist
W. W. Henley, B.S.A., Assistant Animal Hus- J. R. Neller, Ph.D., Biochemist
bandman R. W. Kidder, B.S., Asst. Animal Husbandman
P. T. Dix Arnold, B.S.A., Assistant in Dairy In- Ross E. Robertson, B.S., Assistant Chemist
vestigations SUB-TROPICAL STATION, HOMESTEAD

CHEMISTRY AND SOILS H. S. Wolfe, Ph.D., Horticulturist in Charge
W. M. Fifield, M.S., Assistant Horticulturist
. W. Ruprecht, Ph.D., Chemist** Stacy 0. Hawkins, M.A., Assistant Plant
R. M. Barnette, Ph.D., Chemist Pathologist
C. E. Bell, Ph.D., Associate
H. W. Winsor, B.S.A.. Assistant WEST CENTRAL FLORIDA STATION,
H. W. Jones, M.S., Assistant BROOKSVILLE
W. F. Ward, Asst. Animal Husbandman in
ECONOMICS, AGRICULTURAL Charge*
C. V. Noble, Ph.D., Agricultural Economist**
Bruce McKinley, A.B., B.S.A., Associate
Zach Savage, M.S.A., Assistant FIELD STATIONS

ECONOMICS, HOME
Ouida Davis Abbott, Ph.D., Specialist** Leesburg
L. W. Gaddum, Ph.D., Biochemist M. N. Walker, Ph.D., Plant Pathologist in
C. F. Ahmann, Ph.D., Physiologist Charge
W. B. Shippy, Ph.D., Asso. Plant Pathologist
ENTOMOLOGY K. W. Loucks. M.S., Asst. Plant Pathologist
J. R. Watson. A.M., Entomologist** J. W. Wilson, Ph.D., Associate Entomologist
A. N. Tissot, Ph.D., Associate C. C. Goff. M.S.. Assistant Entomologist
H. E. Bratley, M.S.A, Assistant Plant City
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
HORTICULTURE R. E. Nolen, M.S.A., Asst. Plant Pathologist
A. F. Camp, Ph.D., Horticulturist**
A. L. Stahl. Ph.D., Associate Cocoa
. H. Blackmon, M.S.A., Pecan Culturist A. S. Rhoads, Ph.D., Plant Pathologist
Roy J. Wilmot, M.S.A., Specialist, Fumigation
Research Hastings
R. Dickey, Assistant Horticulturist A. H. Eddins. Ph.D., Plant Pathologist
Monticello
PLANT PATHOLOGY Assistant Entomologist
W. B. Tisdale. Ph.D., Plant Pathologist**
George F. Weber. Ph.D., Plant Pathologist Bradenton
R. K. Voorhees, M.S., Assistant David G. Kelbert. Asst. Plant Pathologist
Erdman West, M.S.. Mycologist
Sanford
*In cooperation with U.S.D.A. E. R. Purvis, Ph.D., Assistant Chemist, Celery
"*Head of Department. Investigations





J








THE PECTIC CONSTITUENTS OF

CITRUS FRUITS
By L. W. GADDUM
CONTENTS Page
Plan of investigation .......................................... ................. 5
Extraction m ethods .................................................................. 5
Effect of maturity on the pectic constituents. .................. ........................
Properties of extracted pectins............ ............................................. 15
Sum m ary and discussion ............................................................. 20
Literature cited .................................................................... 21

INTRODUCTION

The pectic compounds comprise primarily the gelatinizable
substances having their origin in plant cell walls and are charac-
terized chemically by the presence of a galacturonic acid nucleus
in the molecular structure. They form the main constituent of
the middle lamellae of plant cells(1),(8),1 and are intimately in-
volved both in the normal ripening of fruits(2),(6),(8),(9),(15),
(19),(25),(33) and in some pathologic changes due to microor-
ganisms (8), (24),(27), (30),(40).
Three types of pectic compounds are recognized :2
(1) Pectic acids, which are insoluble in water and contain no
methoxyl groups.
(2) Pectins which are methyl esters of pectic acids and are
soluble in water.
(3) Protopectins, which are the water-insoluble, acid-hydro-
lyzable parent substances of the pectins and are present in the
cell-walls of plants, possibly in combination with cellulose(36).
Normal ripening processes (and sometimes pathologic processes)
are accompanied by a gradual transition from the insoluble pro-
topectins to the soluble pectins with a consequent decrease in
cell-wall rigidity. The transition terminates finally in demethy-
lated pectic acids so that over-mature fruits will sometimes con-
tain practically no pectins.
The literature arising from a century of study of pectic com-
pounds has been adequately summarized elsewhere(4),(5),(10),
(11),(28),(34), and consequently a comprehensive resume of the
literature need not be given here. It is of interest, however, to
note certain trends which the study of pectic compounds seems
to be following at the present time.

1Figures in parentheses (Italic) refer to "Literature Cited" in the back
of this bulletin.
2Report of the committee on the nomenclature of pectin, of the Agricul-
ture-Food Division of the American Chemical Society. Sept. 6-11, 1926.







4 Florida Agricultural Experiment Station

The suggestions for a chemical structure of pectic acid, the
basic unit of the pectins, seem to have crystallized into two alter-
natives-the arabinose-galactose-galacturonic acid ring formula
of Nanji, Paton and Ling(23) and the arabinose-galactose-tetra-
galacturonic acid formula of Ehrlich(3),(12),(13),(14). On the
basis of the Nanji, Paton and Ling theory, a completely demethy-
lated pectin (i. e. pectic acid) would have the empirical formula
(C35Ho5033) x; according to Ehrlich, the completely demethylated
pectin from sugar-beets would have the formula (C41HHsO37) and
that from orange peels would have the formula (C39H56036).
According to these two theories, the pectins of varying degrees
of methylation should contain, theoretically, the methyoxyl per-
centages shown below.
Mono- Di- Tri- Tetra-
methylated methylated methylated methylated
Nanji, Paton and Ling ....... 3.06 6.04 8.94 11.76
Ehrlich (sugar beet pectins). 2.68 5.29 7.85 10.35
Ehrlich (orange peel pectins) 2.78 5.49 8.14 10.73

The percentage of calcium in calcium pectate should, according
to these theories, have the following values:
Nanji, Paton and Ling............................. . 7.45
Ehrlich (sugar beet pectins).......................... 6.57
Ehrlich (orange peel pectins) ......................... 6.78

These theoretical values will be discussed later in connection
with experimental data on citrus pectins.
A great amount of study has been devoted also to the physical
properties of the pectic compounds. The viscosity and jellying
power of various fruit pectins have received much attention in
recent years because of the bearing of these properties on the
commercial evaluation of the pectins. This work will be dis-
cussed in connection with the data to which it may be pertinent.
Of the three types of pectic compounds, the pectins alone have
been found of commercial value. The use of the pectins is based
primarily upon the three characteristics: (1) their jellying prop-
erties, (2) their colloid stabilizing properties, and (3) their
power of water imbibition. These characteristics are profoundly
affected by the maturity of the fruit used as source, and by the
method of extraction(17),(20),(21),(22). Work was therefore
planned to study the effect of maturity and fruit type on the
chemical composition and physical properties of the pectins ex-
tracted from different tissues of citrus fruits.

/

I








Bulletin 268, The Pectic Constituents of Citrus Fruits 5

PLAN OF INVESTIGATION

Since the method of extraction influences profoundly the
amount and nature of the pectic materials extracted, it is neces-
sary to employ a uniform extraction method in the study of
maturity and other factors. To this end, the effect of pH, tem-
perature, and time on the yield and quality of extracted pectins
was studied to determine the method of extraction chosen to be
used throughout the work.
To consider the distribution of pectic compounds among the
tissues of the fruit, the fruit was dissected and the various por-
tions extracted separately. The moisture, protopectic and total
pectic contents of the different tissues were then determined by
methods discussed below. Those properties of the extracted
pectins which are concerned in the commercial use of these pectins
were compared for three different fruits (grapefruit, orange,
kumquat). To obtain some indication of any fundamental chem-
ical variations among citrus pectins, some study was given to
the pectic acids obtained from the extracted pectins.

EXTRACTION METHODS

Myers and Baker(22), basing their work on the pioneer work
of Tarr(37), have shown the importance of the pH control in the
extraction of pectins as well as in the manufacture of jelly from
pectins. Accordingly, the pH of the extraction medium, the
temperature, and the duration of the extraction process were
chosen as the dominant variables.
The material to be extracted was dried in vacuo at 600C.,
ground to pass a 100 mesh sieve, and then thoroughly mixed to
provide homogeneous samples.
Since the extracted pectins are subject to hydrolysis by con-
tinued action of the solvent, it was necessary to reduce the time
of action of the solvent on the extracted pectins to a minimum.
Accordingly the following procedure was adopted: 10 grams of
sample were treated with 600 ml. of solvent(22) with rapid stir-
ring at the chosen temperature for 10 minutes; the mass was
then filtered through several layers of silk; as much of the solvent
as possible was pressed from the mass. The extracted pectins
were then removed from the filtrate as discussed below. The
sample residue remaining from the filtration was submitted to
the above extraction process a number of times in succession, the








6 Florida Agricultural Experiment Station

extracted pectic compounds being each time removed from the
filtrate.
The hot filtrate from each of the above extractions was poured
into chilled alcohol (below 15C.) and immediately cooled below
15C. The precipitated pectin was filtered off, dissolved in water,
reprecipitated twice with alcohol, filtered with suction, washed
with alcohol and then with ether, and finally dried to constant
weight in vacuo at 60C. The dried pectic material was then
ground to pass a 100 mesh sieve and analyzed for methoxyl con-
tent by the method of Zeisel, for pectic acid content by the modi-
fied method of Carre and Haynes(7),(16), and for ash content.
To determine the effectiveness of the above extraction method,
a series of experiments were run on samples of lemon, grapefruit,
and orange albedoes. The results for the extraction of lemon
albedo are shown in Table I; the results for the grapefruit and
orange albedoes were practically the same as those for the lemon
albedo.
In the extraction of pectins from the tissues, several factors
come into play: the imbibition of water and subsequent solution
of the cell-wall pectins, the hydrolysis of the dissolved pectins
and the hydrolysis of the cell-wall protopectins.
Table I shows that, for a given pH, an increase of temperature
increases the quantity of pectins extracted. However, the quality
of the extracted pectins deteriorates with increasing tempera-
ture, as shown by the decrease in the ratio of methoxyl percentage
to pectic acid percentage.
Table I shows also considerable variation in the sum of the
pectic acid percentage and the methylene equivalent of the
methoxyl percentage. Since the calculations of Table I are on
an ash-free basis, the sum would approximate 100 percent if the
pectins were chemically pure. In reality, however, the values
range from 74 percent to 93 percent. Norman(26) found that
pectin from lemon juice, after five reprecipitations, contained
over 20 percent of some impurity which he did not identify. It
is of interest in this connection to note that Myers and Baker(22)
were employing pectins containing from 10 percent to 15 percent
impurities when they found no correlation between jellying
power and degree of methylation.
To obviate, to some extent at least, the errors due to impurities
(other than ash), the ratio methoxyl percentage to pectic acid
percentage was calculated. The values shown in Table I for this
ratio indicate that the pectins extracted at pH values from 2.0 to






TABLE I.-DATA SHOWING THE EFFECT OF PH, TEMPERATURE AND TIME ON THE EXTRACTION OF PECTINS FROM LEMON
ALBEDO.

Extracted pectic compounds (% of sample) % pectin in extract
Solvent Temp. -
1* 2 3 4 5 6 7 8 1 2 3 4 5 6 6

Distilled 600C 4.75 3.26 2.91 1.61 1.43 1.06 0.77 0.43 93.10 93.27 92.84 93.1 .........

water 950C 9.76 3.31 2.46 1.53 1.27 0.38 0.11 .... 92.70 93.35 92.86 92.321 92.34 91.36 ;

pH=4.6 boiling 10.37 4.18 2.19 1.82 0.35 0.10 ........ 92.86 92:26 92.42 92.40 ...... 92.58

HCL 600C 5.11 2.75 3.17 1.83 0.96 1.05 0.36 0.12 90.21 89.97...... 90.05 ............

solution 950C 11.25 3.23 2.67 1.90 0.84 0.17 0.14 .... 87.49 87.54 87.14 87.53 87.51 87.25

pH=3.6 boiling 12.43 4.27 2.81 1.64 1.02 0.36 0.11 .... 87.56 87.54 86.64 87.17 87.17 ......

HCL 60C 8.64 3.16 1.23 1.60 0.97 0.82 0.13 0.11 88.35 89.06 ...... 88.79..........

solution 95C 14.36 4.34 1.72 1.23 0.56 0.12 .... .... 82.55 82.47 82.27 82.07 82.37 82.16 o

pH=3.0 boiling 15.21 5.63 2.34 0.97 0.21 0.10 ......... 82.20 82.36...... 82.30 ..... 82.13 .

HCL 60C 9.74 4 21 0.93 1.27 0.72 0.91 0.20 .... 85.07 ..... 86.03 ...... 81.32 n

solution 950C 20.13 4.13 1.37 0.92 0.31 0.11 ........ 75.01 74.45 74.63 74.01 ...... 74.10

pH=2.6 boiling 19.69 7.30 3.72 1.64 0.53 ........ ..... 75.62 74.96 75.1 74.25 74. .....

HCL 95C 20.47 5.13 2.25 1.30 0.21 0.10 .... .....82.45 82.50 82.15 82.01 82.18 82.18 *
solution --- ----
pH =1.9 boiling 22.39 9.77 1.36 0.10 .... ... .... .. 81.44 .... 81.57 ..................

HCL 950C 20.73 6.12 2.32 1.27 0.23 0.51 0.13 .... 85.63 ...... 85.55................
solution --------- ._S
pH=1.2 boiling 20.15 8.93 2.10 0.93 0.37 0.12 ... .... 85.59 ......... 84.91....84.52

HCL 950C 12.11 3.74 0.92 0.14 0.12 .... .... ..... 85.94 85.75 86.20 85.83 ...........
solution -
PH=0.3 boiling 10.91 4.73 0.80 1.03 0.75 0.51 ... .... 86.20 87.03 ...... 85. ..........
*The figures indicate successive extractions.





TABLE I.-DATA SHOWING THE EFFECT OF PH, TEMPERATURE AND TIME, ON THE EXTRACTION OF PECTINS FROM LEMON
ALBEDO.- (Continued.)

% pectic acid % methoxyl Ratio % methoxyl 00
Solvent Temp. in extracted pectins in extracted pectins % Pectic acid
1* 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6

Distilled 60C 87.4987.4387.2087.56 ..... .... 12.8612.4412.4712.35 ..... .... 0.1470.1480.1430.141...... ....

water 95C 87.15 87.7287.4186.9887.0386.0312.29 12.4612.0611.8311.7511.810.1410.1420.1380.1360.1350.137 5

pH=4.6 boiling 87.3086.8586.9287.05 ..... 87.16 12.3111.9812.1711.84 ..... 12.010.1410.1380.1400.136 .... 0.138

HCL 600C 84.2384.08.....84.34..... ..... 13. 08 ..... 12.65........... 0.1570.155 ...0.150..... ...

solution 950C 82.1582.2381.9282.43 82.3182.2011.8311.6811.5511.2911.5211.180.1440.1420.1410.1370.1400.136 .

pH=3.6 boiling 82.1182.1381.4682.0781.8881.5012.0711.9911.4811.3011.71....01470.1460.1410.1380.143.....

HCL 600C 82.3583.12 ..... 82.91 ......... 13.2613.13 ..... 13.02 .......... 0.1610.158.... 0.157..........

solution 950C 77.0977.1776.9276.8377.1176.9512.1011.7311.8511.6011.6411.540.1570.1520.1540.1510.1510.150

pH=3.0 bo ling 76.7976.9176.3276.9876.0376.8911.9812.07..... 11.78..... 11.610.1560.157 .... 0.155 ..... 0.150

HCL 600C 79.28 ..... 80.10 .... ... 75.9312.84 ..... 13.14 .... ...... 11.920.162 ... 0.164 .......... 0.157

solution 950C 70.0269.55 69.7269.1769.4569 2711.0610.8510.8810.72 ..... 10.670.1580.1560.1560.155 ..... 0.154

pH=2.6 boiling 70.4969.8370.1369.3669.51 .... 11.3511.3711.0110.8210.91 .... 0.1610.1600.1570.1560.157 .....

HCL 950C 77.4177.4677.23.....77.16 77.2911.1511.1510.89.... 10.7310.82 0.1440.14410.141.....0.1390.140
solution - -
pH=1.9 boiling 76.50 ... 76.72 .......... ..... 10.94 .... 10.74 .... .... ...... 0.143 .... 0.140 ..............

HCL 950C 81.02 .....81.05..........80.1610.21 .... 9.97 9.75 9.94 .... 0.126 .....0.123...............
solution- ----
pH=1.2 boiling 80.69 .......... 80.39 .... 80.0710.41 10.43..... 10.01 .... 9.850.129........... 0.124... 0.123
HCL 950C 81.9181.87 82.3081.9781.57..... 8.93 8.60 8.64 8.54.......... 0.1090.1050.1050.104.........
solution --------_- _.
pH=0.3 boiling 82.2683.12182.87 82.19 .... ..... 8.72 8.65 .... 8.14.......... 0.1060.104 0.099 ........

*The figures indicate successive extractions.








Bulletin 268, The Pectic Constituents of Citrus Fruits 9

3.0 have higher degrees of methylation than have those pectins
extracted at either higher or lower pH values. By reference to
the data in Table I, it is readily seen that this difference in quality
of the pectins is entirely masked if the methoxyl percentage of
the entire extract pectinss plus impurity) be used as a criterion.
Sucharipa(34) has emphasized the need of pure materials in
working with pectic compounds.
Since, however, the acid extracts containing pectins derived
from protopectins contain also the water-soluble pectins present
in the plant as free pectins, little information can be gained from
the above data as to the state of each of the pectins in the plant.
Accordingly in the routine extraction procedure, the acid extrac-
tions were used on material which had been practically freed from
water-soluble pectins. The uniform extraction procedure chosen
was to employ five successive 10-minute extractions, (1) with
distilled water and (2) with hydrochloric acid solution (pH of 3.6).
Immediately prior to the extraction the weighed sample was ex-
tracted with hot alcohol in a Soxhlet apparatus to remove gluco-
sides, resins and terpenes.

THE EFFECT OF MATURITY ON THE PECTIC
CONSTITUENTS

In studying the effect of maturity on the pectic compounds,
the inner peel (albedo) and the juice sacs (with surrounding
locular walls) were dissected out from the fruit; the juice was
then pressed from the juice sacs. The albedo and the pressed
juice sacs after drying and extracting with hot alcohol were
extracted as separate samples by the uniform method adopted
above. The pectins of the juice were determined by pouring the
juice into chilled alcohol and proceeding according to the uniform
method adopted above. The following data were determined for
each tissue at each sampling date:
(1) Moisture content of tissue.
(2) Methylated pectin (water soluble) content of tissue.
(3) Protopectin (acid-hydrolyzable) content of tissue.
The fruit was picked from the tree on the sampling dates given
and submitted immediately to the laboratory procedure. The
sample, taken from adjacent trees at each date, was divided into
three equal aliquots; the aliquots were dissected separately and
were submitted to exactly parallel procedures. In the case of
the grapefruit, each aliquot consisted of three fruit; in the case








TABLE II.-DATA SHOWING THE EFFECT OF MATURITY ON THE PECTINS FROM ALBEDO, PULP, AND JUICE OF VALENCIA
ORANGES.
Water Extracted Pectins Acid Extracted Pectins Total Extracted Pectins_

Sampling Tissue | a .. a ,a .5 .5 01.5 ".
Date *3 a
-e I. a 0. a .s a a |/ g a s a

Albedo. 65.3 8.71 92.661 11.58| 0.125197.9 20.61 87.181 11.331 0.130192.3 29.3 88.801 11.401 0.128193.9 .
November 15. Pulp... 80.2 10.21 90.941 9.631 0.106195.3 19.61 86.511 9.941 0.115191.0 29.8 1 88.02 9.831 0.112192.5 P
Juice... .... ...... ..... .. .. ... .... .... ..... ...... ..... .... 01 ..... .....| .....I....
Albedo.166.7 14.31 91.811 11.931 0.130197.2 15.91 88.241 12.091 0.137193.7 30.2 1 89.931 12.011 0.134195.36
December21.. Pulp... 181.9 14.71 85.83| 9.441 0.110190.1 14.81 83.121 9.47! 0.114187.4 29.5 84.471 9.451 0.112188.14 .
Juice... I .. ... ..... ..... ..... .... .... ..... ... .. ... .. ... .. .... ... I .. .. ...1..
Albedo.169.4 17,21 93.181 11.551 0.124198.4 12.91 85.141 10.98 0.129191.1 29.7 1 90.941 11.461 0.126196.12
January 14... Pulp...180.1 20.61 91.681 9.991 0.109196.2 9.81 86.44 9.421 0.109190.7 30.4 1 89.991 9.771 0.109194.40
____Juice... ....... ..... ..... ..... ...... ..... .... 071 ... .....I 0.120179.0
Albedo.170.5 20.51 99.771 10.921 0.119196.7 9.61 87.991 11.521 0.131193.2 30.1 1 90.56 11.111 0.123195.58
February 21.. Pulp...183.4 20.31 89.991 9.991 0.111194.5 9.01 89.381 9.56| 0.107193.7 29.3 89.80 9.851 0.109194.25
Juice... .... .... ..... .....I .... .. ..... ..... ..... ...... .... .111 ..... ..... 0.117182.1
Albedo.171.9 21.4 92.071 11.141 0.121197.1 7.71 86.301 11.74! .136191.6 29.1 1 90.541 11.29 0.125195.67
March16..... Pulp... 184.2 18.7! 85.261 8.95[ 0.105189.3 3.31 84.801 9.50 0.112189.1 22.0 I 85.191 9.031 0.106189.27
____Juice.. .... .... ..... ..... ........ ... ..... ..... ......... .131 ..... I ..... 0.110176.3
Albedo.172.8 20.81 90.991 10.651 0.117195.8 9.01 87.241 12.301 0.141192.8 .8 8 89.831 11.151 0.124194.87
April7....... Pulp...184.0 15.31 89.501 8.861 0.099193.5 3.11 84.75 8.721 0.103188.7 18.4 88.701 8.84 0.099192.69 -
Juice... .... .... ..... ..... ..... ... .... ..... ..... ..... ........ 10 0.103177 .3
Albedo. 172.3 19.4| 92.121 10.13| 0.110196.7 6.91 86.241 11.641 0.135191.5 26.3 1 90.581 10.531 0.116195.34 -
May ....... Pulp...186.1 14.61 87.58! 8.231 0.094191.3 1.31 86.481 8.481 0.098190.3 15.9 87.491 8.251 0.094191.22
______ _7 Juice ........ ..... 1 .....1 ..... I ..... I ..... .....I ... ..... .091 .. I ..... .104|78.7
Albedo.172.1 15.31 92.291 10.43! 0.113197.0 5.2! 85.401 11.961 0.140190.8 20,5 I 90.54| 10.81| 0.120195.42
May18 ..... Pulp... 75.0 11.01 91.041 9.201 0.101195.2 5.71 82.491 8.66! 0,105186.4 16.7 88.121 9.011 0.102192.19
Juice... .... ....I ..... ..... ..... .... .... .....I I ...... ........... 7 ... .. 0.099175.3
June ...... Albedo.172.9 13.71 92.35! 10.071 0.109196.9 4.51 85.73! 11.671 0.136191.0 18.2 | 90.711 10.461 0.116195.44
Pulp...173.1 11.2) 85.56/ 8.051 0.043190.2 3.61 84.161 9.171 0.109188.3 14.8 1 85.941 8.321 0.097189.70





TABLE III.-DATA SHOWING THE EFFECT OF MATURITY ON THE PECTINS FROM ALBEDO, PULP, AND JUICE OF NAGAMI
KUMQUATS.
Water Extracted Pectins Acid Extracted Pectins Total Extracted Pectins
S a 1- in w "- w- | M
Sampling Tissue .5
Date w, -" U*


Albedo. 60.1 8.1) 92.94j 12.081 0.130|99.4 25.31 85.481 11.53| 0.135190.7 23.4 | 87.301 11.661 0.133195.57
September6. Pulp... 78.3 7.41 89.701 9.96| 0.111 94.2 20.8/ 86.43! 10.54! 0.122191.2 28.2 1 87.301 10.381 0.119191.99
Juice... .... .... ..... ... ...... ..... ....I ... ... ..... 1...... 0 .01| ..... ..... ..... .....
Albedo.168.3 12.21 91.80 11.291 0.123196.9 19.71 87.101 11.50 0.132192.3 31.9 88.90! 11.411 0.128194.06
October 12.... Pulp...180.2 12.31 89.94! 10.971 0.122194.9 16.8| 85.091 10.21 0.120189.7 29.1 1 87.111 10.521 0.121191.86
Juice... .... .... ..... ..... .... ..... .. ...... .. 0.061 . ..
Albedo.|64.7 20.61 92.53! 11.661 0.126197.8 12.21 85.831 11.671 0.136191.1 32.8 I 90.031 11.66| 0.129195.30
November2. Pulp...179.4 18.71 87.381 9.35| 0.107191.6 9.91 87.31 10.39 0.119192.0 28.6 I 87.341 9.70| 0.111191.72
Juice... ... .... ..... .. ... ..... .... ... ..... .... ..... .... 0.121 ..... I ..... 0.129179.3
Albedo.169.1 27.71 91.951 11.401 0.124197.1 5.3( 86.25| 12.07! 0.140191.7 33.0 1 91.031 11.50! 0.126196.23 Q
December18.. Pulp...181.3 17.31 88.47! 10.701 0.121193.3 8.01 82.71! 10.17 0.123187.3 25.3 I 86.641 10.53! 0.121191.40
Juice... .... .... ...... ..... .... .... ...... ..... .. ... 0 32 ..... 0.134 71.2
Albedo. 68.7 25.31 91.43 10.79| 0.118196.3 7.21 87.76, 12.02| 0.137193.2 32.5 1 90.611 11.061 0.122195.61
January 12... Pulp... 83.0 17.71 89.52! 11.121 0.123194.5 3.01 84.39! 10.63 0.126189.2 20.7 I 88.741 5.671 0.064191.30
Juice... .... .... I ..... ..... [ ..... ... ... I ..... | ..... I ..... .... 0 .28 | ..... .....| 0 .121 77 .5
Albedo. 71.2 23.9 92.20 11.061 0.120197.2 7.2| 85.97 10.92, 0.127190.9 31.1 | 90.77! 11.02| 0.121195.75
February 4... Pulp... J82.4 15.8 87.27 7.591 0.987190.7 2.41 85.541 10.091 0.118190.1 18.2 87.031 7.91 0.091190.60 -
Juice... .... .... .. .... I ..... .... ....I ..... ..... ..... .... 0 .19 ..... ..... 0 .116 180 .7
Albedo.M73.1 20.41 93.58| 10.671 0.114198.4 5.91 85.341 9.641 0.113189.7 26.3 91.711 10.43| 0.114196.42
March 10.... Pulp... 82.7 13.91 88.06| 8.891 0.101192.1 1.71 80.39 8.601 0.107184.3 15.6 87.171 8.85| 0.101191.17
Juice....... .... I .... ... ..... ... ..... .... 0.21 ..... ..... 0.112 79.2
Albedo*|84.6 14.31 93.611 9.921 0.106198.1 0.8 ..... 91.0 15.1 ..... ..... ..... .
April7....... Pulp...185.1 11.21 83.631 8.111 0.097187.3 1.8| 82.971 9.13| 0.110187.1 13.0 83.46, 8.241 0.099187.18 .
Juice........ ..... . .... ..... ..... ..... .... 0.141 ..... .... 0.083174.4
Albedo! .... . .. I..... . .. .. .. ... ... ..... ..... ..... .... ..... ..... .. . .
May10......Pulp...84.3 11.8| 88.08| 8.021 0.091191.7 0.91 82.391 8.571 0.104186.2 12.7 j 87.631 8.051 0.092191.27
Juice... .... .... .... ..... ..... ... ... ..... ..... I ... .. .. .. 0.07 ..... .... 0.067 75.1
*The Albedo at this stage is gelatinous in texture.
tThe Albedo at this stage has practically vanished.







12 Florida Agricultural Experiment Station

of the orange, each aliquot consisted of five fruit, and in the case
of the kumquat, of one hundred fruit.
Some typical results for Valencia oranges and Nagami kum-
quats are shown in Tables II and III.
Tables II and III show that the percentage of total pectic com-
pounds in the albedo and in the pulp remains practically constant
throughout a long portion of the growth period and then gradually
declines; the period of decline begins in the pulp during the early-
ripe stage and in the albedo a little after the full-ripe stage. The
tables show also that the percentage of water-soluble pectins in
the albedo and in the pulp rises to a maximum value and then
declines; in each case the maximum value is reached shortly
before the decline in percentage of total pectic compounds. The
increase in water-soluble pectic content indicates a concomitant
increase in hydrophilic colloids in the outer layers of the cell-
walls(1),(6); according to Reed(32), the translocation of water
takes place by means of these hydrophilic colloids.
In the orange and grapefruit, this conversion of albedo proto-
pectins into pectins occurs more slowly than in the kumquat so
that in the full-ripe orange and grapefruit the albedo retains
considerable rigidity if the normal course of maturing has been
followed. In the full-ripe kumquat, on the other hand, most of
the albedo protopectin has been hydrolyzed, giving the albedo a
gelatinous texture; with the advance of senescence the albedo
practically disappears.
Tables II and III show also that the sum of the pectic acid con-
tent and the methylene equivalent of methoxyl content is close to
97 percent for the albedo extracts, whereas for the juice pectins
(and to some extent for the pulp pectins) the data show the pres-
ence of 15 percent to 22 percent of impurities other than ash.
Moreover the ratio of methoxyl percentage to pectic acid percen-
tage did not remain constant during a series of reprecipitations as
shown by the following representative data for some albedo
pectins (Table IV).
Wendelmuth(39) has demonstrated a decrease in viscosity
accompanying repeated precipitations; Sucharipa(34) and
Myers(22) have shown that two pectins with practically the same
methoxyl content may have widely different viscosities and jelly-
ing-power. These facts have been interpreted by various authors
as being caused by decomposition of the pectins during the puri-
fication process or by differential solubility of the differently
methylated pectins. The fact, however, that in many cases cited
in the literature the sum of the pectic acid content and the methy-







Bulletin 268, The Pectic Constituents of Citrus Fruits 13

lene equivalent of methoxyl content shows evidence of 10 percent
to 20 percent impurity would seem to point to the possibility of a
methoxyl-bearing impurity. Some support might be adduced for
this suggestion by recalling that there have been frequent refer-
ences in the literature to pectins with methoxyl percentages con-
siderably above 11.76 percent (the methoxyl percentage corre-
sponding to Nanji, Paton and Ling's tetra-methylated pectic
acid).
The degree of methylation of the extracted pectins as indicated
by the ratio of methoxyl percentage to pectic acid percentage is,
according to Tables II and III, at all times lower in the water-
soluble pectins than in the acid-extracted pectins. This difference
is least just prior to the decline in total pectic content. No such
pronounced difference is evident in the methoxyl percentages of
the water-soluble and acid-extracted pectins.
The degree of methylation of the water-extracted pectins de-
clines markedly with the progress of maturity in the case of both
the albedo and the pulp. In the case of the acid-extracted pectins,
the ratio shows no definite trend but ranges about an average
value. The water-extracted pectins, reflecting as they do the
gradual conversion of protopectin into methylated pectins, should
show, according to Fellenberg, Carre and others(17),(8), a pro-
gressive demethylation with advancing maturity. On the other
hand, the acid-extracted pectins, being derived directly from the
source material, should reflect the constant composition of the
protopectin. In the case of the kumquat, where the albedo degen-
erates rapidly, even the acid-extracted pectins show evidence of
demethylation.
It is interesting to note that the pectins of lower degree of
methylation are usually of greater purity if the sum of the pectic
acid content and methylene equivalent of methoxyl content be
taken as the criterion. This relation appears to a great extent
also in the data of Myers and Baker(22). These facts seem to
lend some support to the suggestion advanced above that a methy-
lated impurity may be present: (1) precisely in the cases of less
purity is the degree of methylation greatly in excess of the theo-
retical value calculated on the basis either of Nanji, Paton and
Ling's or of Ehrlich's formula and, (2) when one finds the degree
of methylation greatest in the most impure preparations one
naturally suspects either the impurity of contributing methoxyl,
or the pectic acid of having a molecular weight less than that of
the more pure pectins. As shown in Table I, however, the use of













TABLE IV.-DATA SHOWING THE EFFECT OF REPRECIPITATION ON DEGREE OF METHYLATION.

Percent Methoxyl
Ratio
Percent Pectic Acid
Source of Stage of Extractant Precipitation No.
Pectin Maturity ____________

1 2 3 4 5 6 7 8 9
Orange Albedo..... Very Immature Hydrochloric.. .
Acid pH=3.6 0.139 0.135 0.131 0.130 0.127 0.125 0.123 0.124 0.123
rr
Orange Albedo..... Early Ripe..... Water........ 0.120 0.124 ..... 0.131 0.123 .... ..... 0.130

Orange Albedo..... Early Ripe .... Hydrochloric...
AcidpH=3.6 0.140 0.133 ..... 0.130 ..... 0.127 .... ..... 0.125
Orange Albedo..... Over Mature... Water......... 0.107 0.110 ..... 0.112 .... 0.115 0.114 ....

Kumquat Albedo... Very Immature Hydrochloric...
Acid pH =3.6.. 0.119 ..... 0.129 ..... ..... 0.130 ..... ..... 0.130
Kumquat Albedo... Over Mature... Water......... 0.118 ..... 0.123 ..... 0.127 ..... 0.130 ..... 0.130

Grapefruit Albedo. Very Immature Hydrochloric.. .
AcidpH=3.6.. 0.142 0.138 0.135 0.134 0.134 ..... 0.133 0.134 .....
Grapefruit Albedo.. Full Ripe...... W ater ........ 0.121 ..... 0.119 ..... ..... .. 0.117 ... ..







Bulletin 268, The Pectic Constituents of Citrus Fruits 15

more concentrated acids results in greater pectic acid percentage,
smaller methoxyl percentage, and greater purity (according to
the criterion adopted above). This would seem to indicate the
presence in the extract of a methoxyl-bearing impurity which
appears also in the calcium pectate precipitate from which the
pectic acid percentage is obtained.
The pectins in the juice are, in general, of low quality and
present in small percentages. An exception occurs in the case
of the kumquat, where at full maturity the pectin content
of the juice sometimes reaches 0.32 percent while the ratio
percent methyoxl r
percent pectic acid
Table II shows that the ratio of methoxyl content to pectic acid
content reaches in the juice of the orange a maximum value of
0.120 in the pre-ripe stage, falling to a value of 0.097 in the full-
ripe stage. Norris(29) states that the pectins of orange juice
have an average methoxyl content of 8.92 percent. Norris, how-
ever, as pointed out by Norman(26), did not calculate his meth-
oxyl content on the basis of the actual pectic acid content; as indi-
cated in a prior discussion, calculations based upon the total
sample weight (which includes impurities) frequently give mis-
leading results. Moreover, Norris did not consider the effect of
maturity. As shown in Table II, the juice pectins of the orange
are at one stage of maturity probably tri-methylated; the table
shows also that at an earlier stage they were almost tetra-methy-
lated and at a later stage practically di-methylated.
Tables II and III show that at any stage of maturity, the degree
of methylation of the pectins is greatest in the albedo and least
in the juice. Fellenberg(17) deduced from the methoxyl per-
centage that albedo pectins were more highly methylated than
pulp pectins. No criterion of purity (Ca pectate determination)
was available to Fellenberg, however, and calculations based upon
methoxyl percentage of total sample are untrustworthy as shown
above.
PROPERTIES OF EXTRACTED PECTINS
As the above data show, the amounts of free methylated pectins
and of pectins derivable from protopectins present in the tissue
vary with maturity; the properties also of these extracted pectins
vary with maturity. The following properties of the extracted
pectins were studied: 1, viscosity; 2, jelly strength; 3, the ratio
Ca
Ca pectate








16 Florida Agricultural Experiment Station

The viscosity measurements were made on 0.5 percent solutions
at 250C. by means of an Ostwald viscosity pipette. The jelly
strength measurements were made by means of the device de-
scribed by Tarr(38); the jellies were prepared according to the
standard method of Myers and Baker(22). The values of the
ratio Ca were determined by analysis for calcium of the
Ca pectate
calcium pectate precipitate of the Carre and Haynes procedure
for the determination of pectic acid.
Table V shows, for the water-soluble pectins, a close correla-
tion between viscosity, jelly-strength and degree of methyla-
tion. The data for the acid-extracted pectins indicate a fair
correlation among these properties, but by no means so close as
in the case of the water-soluble pectins. In Fig. 1 are plotted the
data: jelly strength versus the degree of methylation.
As shown in Table I, the acid-extracted pectins contain much
more non-pectic material than do the water-extracted pectins. It
is not strange, therefore, that these more impure pectins should
show greater variation than the comparatively pure water-soluble
pectins.
JELLY
0 STRENGTH
CMS. OF WATER

170 e
e e



130



90





0 WATER EXT. ORANGE
s KUM UAT
ACID ORANGE
KUMQUAT %METHOXYL
30 PECTICC ACID
.130 .o .A .1o .15 .135 .1o .l4s
Fig. 1.-Graph showing jelly strength and methoxyl content of pectin of
oranges and kumquats.












TABLE V.-DATA SHOWING THE EFFECT OF MATURITY ON ORANGE AND KUMQUAT PECTINS.

% methoxyl
Ratio ------ Viscosity* Jelly Strengtht
Fruit Date % pectic acid
Water extracted Acid extracted Water extracted Acid extracted Water extracted Acid extracted
pectins pectins pectins pectins pectins pectins

November 15. 0.125 0.130 14.83 18.82 106 160
December 21.. 0.130 0.137 20.10 21.13 140 150
January 14... 0.124 0.129 13.42 19.50 94 146
Orange... February 21.. 0.119 0.131 11.21 20.44 64 138
March 16..... 0.121 0.136 19.93 20.27 85 174
April 7....... 0.117 0.141 9.85 21.01 68 162
May1....... 0.110 0.135 6.04 20.73 42 154
June 5....... 0.109 0.136 5.12 19.41 38 152

September 6.. 0.130 0.135 19.43 18.43 145 134
October 2 .... 0.123 0.132 13.05 19.51 97 155
November 2.. 0.126 0.136 15.97 20.62 109 143
Kumquat.... December 18.. 0.124 0.140 14.02 22.29 99 173
January 12... 0.118 0.137 10.11 19.12 70 158
February 4... 0.120 0.127 11.74 19.71 94 149
March 10..... 0.114 0.113 7.06 16.85 56 115
_April 7....... 0.106 ..... 4.27 18.91 37 128
*Relative viscosity.
tIn centimeters of water height.

t"







18 Florida Agricultural Experiment Station

Myers and Baker(22), working with the mixture of water-sol-
uble and acid-extracted pectins, obtained no clear correlation
between jelly-strength and degree of methylation of pectins ex-
tracted at different pH values. The data in Table V are not
necessarily in conflict with Myers and Baker's results, since all
the acid-soluble pectins referred to in Table V were extracted at
the same pH but from different fruit and at different stages of
maturity. Moreover, acid-extraction in the pH range 2.0 to 3.0
results in considerable impurity of the extracted pectin as shown
in Table I, and as shown also in Myers and Baker's data; this
would introduce some irregularities in subsequent measurements.
In fact, as shown in Table I, any correlation existing between jelly
strength and the methoxyl content of the pectins would be com-
pletely masked if the calculations of methoxyl content were based
on the total sample pecticc acid plus impurity).
The data reported in Table V are in agreement with the results
of Sucharipa(35) and Wendelmuth(39) except that these authors
employ methoxyl percentage rather than the ratio used above.
For water-extracted pectins, because of the greater purity attain-
able, this difference is probably of no significance. Because of
the close agreement between Sucharipa's results and the data of
Poore(31) obtained with obviously excellent pectins, we must
assume that Sucharipa's pectins were of high purity.
Table VI shows the calcium content of calcium pectate obtained
from pectins which had been reprecipitated with alcohol (con-
taining no acid). The calcium pectate was in each case prepared
precisely according to the procedure of Carre and Haynes(7).
The data show, in the case of the water-soluble albedo pectins,
that the calcium content of calcium pectate decreases on repeated
purification to approximately the value calculated from the Nanji,
Paton and Ling formula for pectic acid and obtained by Carre
and Haynes for apple pectin. The initial high results are due
probably to the presence of ash; the fall in calcium content seems
to be paralleled by a fall in ash content.
In the case of the acid-extracted pectins, considerable impurity
other than ash was present; the fall in ash content accompanying
repeated purification was not paralleled by a corresponding change
in the calcium content of calcium pectate. Moreover, repeated
purification caused the pectins to yield lower values for the cal-
cium content of calcium pectate; boiling the purified pectin with
hydrochloric acid at a pH of 2.6 caused the pectins to yield higher
values. Whether the impurity present originally in the acid-









TABLE VI.-DATA SHOWING EFFECT OF REPRECIPITATION ON CALCIUM CONTENT OF VARIOUS CALCIUM PECTATES.

Percent Calcium in Calcium Pectate
Source of Stage of Extractant Precipitation No.
Pectin Maturity 1 _9
1 2 3 4 5 6 7 8 9

Orange Albedo..... Immature..... Water......... 7.93 7.71 .... 7.62 ... 7.50 .... 7.49 ....

Orange Albedo..... Immature..... Acid.......... 8.76 .... 8.06 .... 7.91 7.72 7.52 .... 7.54 3

Orange Albedo..... Early Ripe... Water......... 8.03 .... 7.67 .... 7.52 .... 7.42 7.41

Orange Albedo..... Early Ripe.... Acid.......... 8.92 8.31 .... 7.73 7.64 7.52 ... 7.53 ...

Orange Albedo..... Overripe....... Water......... 9.01 8.47 .... 8.09 7.88 7.76 7.65 7.63 7.60
0
Kumquat Albedo... Immature..... Water......... 7.76 .... 7.66 .... 7.54 7.48 7.46 ....

Kumquat Albedo... Immature.... Acid.......... .... 8.31 .... 7.68 7.60 .... 7.58 7.61 ....

Grapefruit Albedo.. Immature... Water......... 7.81 7.70 .... 7.63 .... 7.51 7.49 7.47 ...

Grapefruit Albedo.. Immature... Acid.......... 8.17 7.95 .. 7.72 .... 7.54 ... 7.57 .

Grapefruit Albedo. Early Ripe.... Water......... 8.15 ... 7.82 7.59 7.52 ... 7.50

Lemon Albedo..... ? Water........ 7.91 7.73 .... 7.60 7.54 .... 7.50 7.52

Lemon Albedo..... ? Acid.......... 8.21 .... 7.95 7.83 .... 7.73 ... 7.61 7.59 w

OrangePulp....... Immature..... Water......... 9.32 .... 8.41 8.02 .... 7.81 7.65 7.60 7.57

Orange Pulp...... Immature..... Acid.......... 9.14 .... 7.87 .... 7.73 7.62 .... 7.59 7.62 S
I-
(0







20 Florida Agricultural Experiment Station

extracted pectin is a decomposition product of pectic acid is
uncertain; the data shown in Tables I and IV would seem to
suggest that the contrary is true, since demethoxylation would
be presumed to precede other decomposition of pectic acid.

SUMMARY AND DISCUSSION

The foregoing data indicate (1) that in the fruits studied,
(orange, grapefruit and kumquat) the percentage of total pectic
compounds in the albedo and in the pulp remains constant through
a considerable portion of the growth period; (2) that the per-
centage of water-soluble pectins in these tissues rises to a max-
imum value just prior to the decline in total pectic content, and
then gradually declines; and (3) that the rate of conversion of
protopectin into water-soluble pectins is greater in the pulp than
in the albedo. Carre(8), Conrad(9), and others have demon-
strated the above facts concerning the percentages of pectic
materials in whole fruits; the above data seem to indicate that
the relations established by the above workers are valid for each
tissue separately (at least, for the albedo and the pulp).
Qualitatively it was observed also that the dried pulp tissues
were more hygroscopic than the dried albedo tissues. If, as
indicated by Reed3(32), the hydrophilic colloids of the cell-walls
and middle-lamellae serve as avenues for the translocation of
water, then the difference in water-absorbing capacity existing
at two points would seem to condition the direction and rate of
water-translocation between those two points. On this basis, the
difference in rates of protopectin conversion referred to above
would have a direct bearing on the direction and rate of translo-
cation. The action of gases such as nitrogen and carbon dioxide,
which according to Carre and Horne(8) accelerate decomposition
of pectic compounds, would thus be significant in the disturbance
of water-distribution throughout the fruit.
The data presented herewith show also (1) that the degree of
methylation is less in the water-extracted pectins than in the
corresponding acid-extracted pectins; (2) that the degree of
methylation of the water-extracted pectins declines as maturity
of the fruit progresses while that of the acid-extracted pectins
remains fairly constant; and (3) that the degree of methylation
(and also purity) of the pectins extracted from the pulp is less

3Reed states "the locule walls are cellulose." He probably means, how-
ever, "cellulose and pectic compounds."







Bulletin 268, The Pectic Constituents of Citrus Fruits 21

than that of pectins from the albedo and greater than that of
pectins from the juice. Moreover, it has been shown that repre-
cipitation does not produce always a lower degree of methylation
as suggested by Wendelmuth(39) nor always a higher degree as
suggested by Myers and Baker(22). In fact, there were used in
this work many pectins (and many also have been reported in
the literature) with a degree of methylation considerably above
that required by the molecular structure assumed by either Nanji,
Paton and Ling, or Ehrlich. This would seem to militate either
against the validity of the postulated structures or against the
practice of assuming that high methoxyl content indicates ab-
sence of pectin decomposition. Some support might be adduced
for the latter hypothesis by noting that in most cases those pec-
tins with methoxyl percentages higher than Nanji, Paton and
Ling's theoretical value decreased in methoxyl content upon re-
precipitation.
For the water-extracted pectins, a very close correlation was
found between viscosity and degree of methylation and between
jelly strength and degree of methylation. For the acid-extracted
pectins, only fair correlations were found. There is some dis-
agreement in the literature as to the existence of the above corre-
lations; these differences might disappear if the degree of methy-
lation were considered on the basis of actual pectic acid present.
The percentage of calcium present in the calcium pectates de-
rived from the various reprecipitated pectins approached a value
between 7.40 and 7.60. These values are in fair agreement with
the value given by Carre for apple pectin; they accord reasonably
also with the Nanji, Paton and Ling theoretical value of 7.45.

LITERATURE CITED
"T 1. ALLEN, CHARLES E. On the origin and nature of the middle lamella.
Botannical Gazette 32: 1-34. 1901.
2. APPLEMAN, C. 0., and C. M. CONRAD. The pectic constituents of toma-
toes and their relation to the canned product. Univ. of Maryland, Agr.
Exp. Sta., Bul. 291. 1927.
3. BOWMAN, J. R., and R. B. McKINNIS. A study of the pentose and acid
content of orange albedo and an arabino-galacturonic acid derived from
orange pectin. Jour. Am. Chem. Soc. 52: 1209-15. 1930.
4. BRANFOOT, M. H. (M. H. CARRE.) A critical and historical study of the
pectic substances of plants. Food Investigation Board, Special Report
33, Department of Scientific and Industrial Research. His Majesty's
Stationery Office, London, 1929.
5. BRIDEL, MARC. Les recent travaux sur la constitution des pectines.
Journ. de Pharm. et de Chim. (8) 13: 99-129. 1931.
" 6. CARRE, M. H. An investigation of the changes which occur in the pectic
constituents of stored fruit. Biochem. Jour. 16: 704-712. 1922.








22 Florida Agricultural Experiment Station

7. CARRE, M. H., and DOROTHY HAYNES. The estimation of pectin as cal-
cium pectate and the application of this method to the determination
of the soluble pectin in apples. Biochem. Jour. 16: 60-69. 1922.
4 8. CARRE, M. H., and A. S. HORNE. An investigation of the behavior of
pectic materials in apples and other plant tissues. Ann. Botany 41:
193-237. 1927.
9. CONRAD, C. M. A furfural-yielding substance as a splitting product of
protopectin during the ripening of fruits. Plant Physiology 5: 93-103.
1930.
10. DORE, W. H. Recent progress in the chemistry of pectin and its indus-
trial applications. Jour. Ind. and Eng. Chem. 16: 1042. 1924.
11. DORE, W. H. The pectic substances. Jour. Chem. Education 3:505-
513. 1926.
12. EHRLICH, F., and R. VON SOMMERFELD. Composition of the pectic
substances from the sugar beet. Biochem. Zts. 168: 263-323. 1926.
13. EHRLICH, F., and F. SCHUBERT. Uber Tetra-Araban und seine Bezie-
hung zur Tetra-galacturonsaure, dem Hauptkomplex der Pektinstoffe.
Biochem. Zts. 203: 343-350. 1928.
14. EHRLICH, F., and A. KOSMALHY. Uber die Chemie des Pektins der
Obstfruchte. Biochem. Zts. 212: 162-239. 1929.
15. EMMET, A. M. An investigation of the changes which take place in
the chemical composition of pears stored at different temperatures, with
special reference to the pectic changes. Ann. Botany 43: 269-308. 1929.
16. EMMET, A. M., and M. H. CARRE. A modification of the calcium pectate
method for the estimation of pectin. Biochem. Jour. 20: 6-12. 1926.
17. FELLENBERG, TH. VON. Uber die Konstitution der Pektink6rper. Bio-
chem. Zts. 85: 117-161. 1918.
18. GRIEBEL, C., and F. WEISS. The pectin question. Z. Untersuch.
Lebensm. 58: 189-201. 1929.
S19. HALLER, M. H. Changes in the pectic constituents of apples in relation
to softening. Jour. Agr. Res. 39: 739-46. 1929.
20. JOHNSTIN, RUTH, and M. C. DENTON. The relation of alcohol precipi-
tate to jellying power of citrus pectin extracts. Jour. Ind. Eng. Chem.
15: 778-80. 1923.
21. MEHLITZ, A. Pectins. Kolloid Zts. 41: 130-46. 1927.
22. MYERS, P. B., and G. L. BAKER. Fruit Jellies. VI. Role of pectin. 2.
Extraction of pectin from pectic materials. Delaware Agr. Exp. Sta.,
Bul. 160. 1929.
23. NANJI, D. R., F. J. PATON and A. R. LING. Decarboxylation of poly-
saccharide acids; its application to the establishment of the constitution
of pectins and to their determination. Jour. Soc. Chem. Ind. 44: 253-8 T.
1925.
24. NEUBERG, CARL, and B. OTTENSTEIN. Formation of methanol in the
autolysis of fresh tobacco leaves. Biochem. Zts. 197: 490-501. 1928.
25. NIGHTINGALE, G. T., R. M. ADDOMS and M. A. BLAKE. Development and
ripening of peaches as correlated with physical characteristics, chemical
composition, and histological structure of the fruit flesh. III. Macro-
chemistry. New Jersey Agr. Exp. Sta., Bul. 494. 1930.
26. NORMAN, A. G. Studies on pectin. III. The degree of esterification
of pectin in the juice of the lemon. Biochem. Jour. 22: 749-52. 1928.
27. NORMAN, A. G. The biological decomposition of pectin. Ann. Botany
43: 233-43. 1929.
28. NORMAN, A. G. Biochemistry of pectin. Science Progress 24: 263-79.
1929.
S29. NORRIS, F. W. The pectic substances of plants. IV. The pectic
substances in the juice of oranges. Biochem. Jour. 20: 993-997. 1926.
4 30. PITMAN, G. A., and W. V. CRUESS. Hydrolysis of pectin by various
microorganisms. Jour. Ind. Eng. Chem. 21: 1292. 1929.








Bulletin 268, The Pectic Constituents of Citrus Fruits 23

S31. POORE, H. D. Citrus pectin. U. S. D. A., Bul. 1323. 1925.
f 32. REED, H. S. The swelling of citrus fruits. Amer. Jour. of Botany
17: 971-82. 1930.
33. ROSA, J. T. Changes in composition during ripening and storage of
melons. Hilgardia 3: 421-43. 1928.
34. SUCHARIPA, R. Die Pektinstoffe. (Braunschweig, 1925.)
35. SUCHARIPA, R. Experimental data on pectin-sugar-acid gels. Jour.
Assoc. Off. Agr. Chem. 7: 57. 1923.
%-36. SUCHARIPA, R. Protopectin and some other constituents of lemon peel.
Jour. Am. Chem. Soc. 46: 145-56. 1924.
37. TARR, L. W. A study of the factors affecting the jellying of fruits.
Delaware Agr. Exp. Sta., Bul. 133. 1923.
38. TARR, L. W. Fruit jellies III. Jelly strength measurements. Dela-
ware Agr. Exp. Sta., Bul. 142. 1926.
39. WENDELMUTH, GERTA. fber die Gelierfihigkeit von ObstsRften und
pektinlbsungen. Kolloidchemische Beihefte 19: 115-137. 1924.
t 40. WILLIMAN, J. J. Enzymic relations of pectin. Univ. of Minnesota.
Studies Biol. Sci. 6: 333-41. 1927.





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