The Lemon Fruit [Reprint 2020 ed.] 9780520346994

Citation preview

The Lemon Fruit

University of California

• College of Agriculture

University of California Press Berkeley and Los Angeles • 1951

Lemon Fruit Its Composition, Physiology, and Products

ELBERT T. BARTHOLOMEW PROFESSOR EMERITUS

O F P L A N T P H Y S I O L O G Y AND

PLANT PHYSIOLOGIST, EXPERIMENT STATION,

RIVERSIDE

WALTON B. SINCLAIR BIOCHEMIST, EXPERIMENT

STATION,

RIVERSIDE

University of California Press Berkeley and Los Angeles California Cambridge University Press London, England o Copyright, 1951, by The Regents of the University of California

P R I N T E D IN T H E U N I T E D STATES OF AMERICA B Y T H E U N I V E R S I T Y O F C A L I F O R N I A PRESS D E S I G N E D B Y A. R .

TOMMASINI

PREFACE

A

/ ALTHOUGH NOT edible in the same manner as most other citrus fruits and deciduous fruits, the lemon probably has a greater variety of culinary, beverage, industrial, and medicinal uses than any other fruit. Published investigations on the lemon fruit are widely scattered in the literatureThe major results presented in these widely scattered publications are brought together here in such a manner that they present a more or less complete and up-to-date summary of our present general and technical information concerning the lemon fruit. The data as assembled should be of value not only to the producer, shipper, and consumer but to the scientist to guide him in future research work on this important fruit. All analytical data are, of course, not included, but enough are given to show average values and trends. For further details the reader may refer to the literature cited. The results of the investigations given apply primarily to lemons grown in the United States, but some comparisons are made with foreign lemons, and in some instances the composition of the lemon is compared with that of other species of citrus fruits. 1

See "Literature Cited" for citations, referred to in the text by author and date, v •

vi

Preface

Unless otherwise indicated, the term "lemon' refers to the fruit alone and to the fruit of the acid lemon only (Citrus limonia, Linn.). In general, no attempt is made to indicate varietal differences in composition. This procedure appears to be justified because the differences in varietal composition that have been reported in the past are often no greater than the differences between various samples from a single variety grown under various conditions in different localities. The data and discussions for a few of the subjects presented here are less extensive than for the others. In such cases only a limited amount of investigational work had been done previously. The data for some of the recent work are being published here for the first time. For a more complete discussion of the origin, distribution, varieties, and similar information concerning the lemon, the reader is referred to The Citrus Industry, Vol. I (Webber and Batchelor, 1943), and for discussions concerning orchard practices, diseases, insect pests, and similar topics, see Vol. II of the same publication (Batchelor and Webber, 1948).

The authors gratefully acknowledge their indebtedness to the following persons who read the entire manuscript and made helpful suggestions and criticisms for its improvement: Dr. L. D. Batchelor, Director of the University of California Citrus Experiment Station, Riverside, California; Dr. M. A. Joslyn of the University of California, Division of Food Technology, Berkeley, California; Dr. Glenn H. Joseph, Director of the California Fruit Growers Exchange Lemon Research Laboratory, Corona, California, and Dr. E. F. Bryant of the same laboratory; Mr. J. R. MacRill, Head of the Field Service Laboratory of the California Fruit Growers Exchange, Ontario, California; also to Mr. W. E. Baier and Mr. R. H. Higby of the California Fruit Growers Exchange Research Laboratory, Ontario, California, who gave constructive criticisms on the sections on "Hesperidin" and "Vita-

Preface

vn

mins"; and to Mr. H. W. Nixon, Supervisor of Lemon Inspection, California Fruit Growers Exchange, Los Angeles, California, who made helpful suggestions for the improvement of the section on "General Information." The authors are greatly indebted to Miss Margaret Buvens, Librarian at the University of California Citrus Experiment Station, Riverside, California, for checking and editing the literature citations; to Jordan Brotman, Office of Agricultural Publications, Berkeley, California, for editing the manuscript; and to Amadeo R. Tommasini, Superintendent of the University Press, Berkeley, California, for designing and supervising production of the book. Finally, sincere appreciation is expressed to those who gave permission to reproduce herein certain of their figures and tables, and to all others, though not specifically mentioned, who helped in many ways to make this publication possible.

CONTENTS

I . G E N E R A L INFORMATION

1

Origin and History Distribution and Production Variety Fruit Set and Harvest Maturity Defined Storage Structure Relative Proportions of Peel and Pulp Age vs. Size Growth-Promoting Substances and Fruit Size Chemical Changes Interpretation of Data I I . COMPOSITION AND PHYSIOLOGY

. . .

1 2 3 3 4 5 6 8 9 10 11 12 13

Specific Gravity

13

Whole fruit

13

Juice

16

Color in Peel

17

Lipids

19

L i p i d s in peel

21

Lipids in juice

21

Lipids in seeds ix •

.

.

.

.

22

x

Contents Essential Oil

23

Oil in peel

24

Oil in juice vesicles

•

29

Hesperidin

31

Limonin and Nomilin (Bitter Principles) Moisture Moisture in whole fruit Moisture in peel

. . . .

34 35 35

.

.

.

.

41

Moisture in juice .

.

.

.

43

Storage, Effect on Juice Quantity Respiration Starch

43 46 58

Soluble Solids Sugars

58 64

Sugars in peel

64

Sugars in juice

.

.

.

.

pH Organic Acids and Buffer Properties Acids in peel

67

72 74 74

Acids in extracted juice

•

80

Polysaccharides Pentosans Pectin

89 92 94

Pectin in peel

95

Pectin in pulp

103

Pectin in juice

105

Cellulose and Hemicellulose Proteins

109 113

Proteins in whole fruit (minus seeds)

113

Proteins in peel

115

•

Proteins in edible portion

115

Proteins in juice

.

.

.

.

116

Proteins in seeds

.

.

.

.

116

Glutathione Enzymes

117 119

Contents

xi

Vitamins

122

Inorganic Constituents

128

Total ash

128

Common elements

129

Trace elements

132

Alkaline ash of lemon juice Seeds

•

I I I . PRODUCTS AND T H E I R USES

132 134 136

Whole Fruit

137

Stock feed

137

Pectate pulp Pectic acid

137 .

.

.

.

137

Vitamin C

138

Press liquors

138

Peel

139

Essential oil

139

Pectin

139

Candied peel

140

"Vitamin P "

140

Enzymes

140

Galacturonic acid

140

Juice

141

Citric acid

141

Beverages

142

Other uses

142

Seeds

;

142

Oil

142

Peroxidase

143

Stock feed

143

L I T E R A T U R E CITED

144

AUTHOR INDEX

157

S U B J E C T INDEX

161

Chapter I

GENERAL INFORMATION

Origin and

History

has existed for so long that its origin is not known. Swingle (see Webber and Batchelor, 1943, p. 399) has the following to say with reference to its origin: " . . . Probably the lemon should be considered as a satellite species [a species of doubtful validity] of the citron; possibly it may prove to be of hybrid origin, perhaps having the citron and lime for parent species. As is true with the grapefruit, it is difficult to explain the origin of the lemon as a hybrid, as it crosses readily with other species of Citrus and yet, when self-pollinated, reproduces itself from seed with only very small variations. . . . " I H E LEMON

That the first-known habitat of the lemon was Southeastern Asia, probably Southern China and Northern Burma, appears to have become fairly well established. It was introduced by the Arabs into Persia and Palestine where it was widely grown by the beginning of the twelfth century. From these countries it was apparently taken into Spain, North Africa and the Canary Islands. The lemon entered the United States, probably indirectly, from the island of Haiti where it had grown from seeds brought from the island of Gomera, one of the Canary Islands group, by Colum1 •

The Lemon Fruit bus on his second voyage, 1493. A much more detailed discussion of the interesting historical story of the spread of the lemon from its natural habitat into other parts of the world is given by Webber and Batchelor, 1943 (see especially pages 6, 7-9, 10, 20).

Distribution

and

Production

Lemons are grown in limited amounts for home use in almost every area where citrus can be grown but their commercial production is confined principally to three countries, Italy, Spain, and the United States. Since 1938 the United States has been the world's largest producer of lemons. Their production in the United States is confined almost exclusively to California. According to the California Fruit Growers Exchange (1947, 1950), the five-year-average number of boxes of lemons produced in California and Arizona between 1924 and 1944 has been as follows: Years

Boxes

1924-29

6,500,000

1929-34

1934-39

7,100,000

9,300,000

1939^4

13,400,000

Since 1944 the annual yields of California and Arizona lemons, in round numbers, have been as follows : Year

Million boxes

1944-15

1945-16

1946-47

1947-48

194S-49

1949-50

12.6

14.5

13.8

12.9

9.9

11.4

During the last three of these years, approximately two-thirds of the crop was consumed as fresh fruit. The standard shipping weight of a box of California or Arizona lemons is 79 pounds; previous to 1943 it was 76 pounds. The lemon acreage in Arizona is small but is increasing. According to a recently published survey (June 2,1949) the present plantings total 814 acres. Whole groves of lemon trees in Arizona are rather rare. Most of the trees are planted in single or double

General Information rows in or bordering groves of other varieties of citrus (for reference see "Literature Cited," under "Arizona Citrus"). The State of Texas also produces a limited supply of lemons, most of which are consumed locally.

Variety The Eureka is the principal variety of lemon grown in California. Of the total acreage of lemons in California in 1946 approximately 88 per cent consisted of Eurekas, 8 per cent of Lisbons, 2 per cent of Villafrancas, and 2 per cent of all other varieties. The Eureka variety gained predominance because of its superior quality and productiveness in most areas, and because it matures a considerable quantity of its fruit during late spring and in the summer when demand and prices are at a maximum. The Lisbon variety is preferred in south central California and some new plantings of this variety have been made in Arizona. Having a relatively dense foliage its fruit is less susceptible to such factors as sunburn and freeze injury. As a result of their studies on the relative susceptibility of different species and varieties of citrus to freeze injury in California during the winters of 1947-48 and 1948-49, Hodgson and Wright (1950) found that the Eureka lemon was more susceptible to freezing temperatures than either the Lisbon or the Villafranca. Because of its other predominant favorable qualities it is not probable, however, that the Eureka's greater susceptibility to freeze injury will prevent it from being the principal choice for future plantings.

Fruit Set and Harvest The lemon tree in California blooms and sets its fruit more or less continuously the year around, but the heaviest sets

The Lemon Fruit occur in the spring and fall. In southern California pickings are usually made every six to eight weeks throughout the year, but in the south central California and Arizona areas the pickings are mostly limited to a period of only four months, October to January.

Maturity

Defined

In most species or varieties of fruits it is not difficult to distinguish by looks or taste the differences between those that are immature and those that are mature. As applied to lemon fruits, however, the terms "immature" and "mature" are rather vague. The generally accepted maturity test is based on the availability of extractible juice. According to State regulations in California and Arizona a lemon that contains a minimum of 25 per cent of juice by volume is considered to be mature, regardless of size or color. Supply and demand would not make it profitable to pick all fruits just as soon as they contain that amount of juice; they are therefore picked according to size. The rings used to determine the size of the fruit range from 2%2r/ to 2%2" in diameter, but the ones most commonly used are ', JS ® S? ¿3 ® j ï til £ > M £ i» 3 O i » 3 O ^H IN CO Hi IO CO

o

o M

The Lemon Fruit amount of moisture passes from the fruit into the surrounding air, and, of course, no moisture is absorbed from the storage room by the fruit. The increase in the amount of juice that can be reamed from the fruit at the end of any given storage period, therefore, must be caused by physical and chemical changes which release moisture in the surrounding tissues, mainly in the peel, from where it migrates into the juice sacs. (For moisture that may be lost from peel during storage, see table 9, col. 2, p. 62.) The increase in the amounts of juice on a weight- or milliliterper-fruit basis that may be reamed from lemons that have been kept in commercial storage for different lengths of time is shown in tables 6 and 7. There was considerable variation in the relative responses of the silver, light-green, green, and dark-green fruits but, with two exceptions (table 6 ) , each lot showed an appreciable increase in yield of juice per fruit. The two exceptions were the silvers in No. 3 and the dark greens in No. 5. Values in table 6 show that the average maximum increase in amount of juice per fruit was 27.8 per cent for silvers, 30.6 per cent for light greens, and 31.3 per cent for dark greens. Values in the first part of table 7 show similar but slightly lower increases.

Respiration Generally speaking, the rate of respiration in citrus fruits is lower than in most other fruits and in vegetables. The ascending order of rates of respiration for citrus fruits has been found to be grapefruit, Valencia oranges, lemons and navel oranges (Hendrickson and MacRill, 1948). Some of the factors which have been found to influence the rate of respiration of lemon fruits, and hence their keeping quality in storage, are: the type of soil on which grown, cultural practices, portion of tree on which they have grown, age when placed in storage, washing, sterilizing, waxing, degreening, and the temperature and humidity at which they are stored.

Composition and Physiology In Gore's tests ( 1 9 1 1 ) , stored lemons gave off a maximum of carbon dioxide at 29.3° C ( 2 0 m g / k i l o / h r . ) and a minimum at 1.7° C ( 2 m g ) . The average rates of respiration of lemons stored at different temperatures were found by Haller, Harding, Lutz and Rose ( 1 9 3 1 ) to be as follows: Temperature °F

32 40 50 60 70 80

Mg CO2 per kg per hr.

Sensible heat, Btu per ton per 24 hr.

2.65 3.70 10.50 13.5 18.6 28.2

580 810 2310 2970 4090 6200

The heats of respiration (Btu per ton per 2 4 hours) were calculated from the C0 2 values (mg CO2 per kg of material per hours x factor 2 2 0 ) . The calculations were made on the assumption that the heat liberated in the respiration process is produced by the oxidation of a hexose sugar according to the following equation: CeHisOo + 6 O2 = 6 CO2 + 6 H2O + 6 7 3 Cal. The heat capacity, or specific heat, of lemons is composed of approximately 90 per cent heat of respiration and 10 per cent latent heat. Using these and other data of Haller et al. ( 1 9 3 1 ) , Hendrickson and MacRill ( 1 9 4 8 ) constructed the respiration curves shown in figure 9. The figure shows that the heat of respiration is a function of temperature, and that the rate of respiration of the lemon is variable and although somewhat higher than that of the grapefruit, considerably lower than that of the navel orange. While figure 9 shows that the rate of respiration increases rapidly in navels, lemons and grapefruit as the storage temperatures are increased from 32° to 80° F, Gonzalez ( 1 9 4 8 ) has shown that freezing temperatures also increase the rate of respiration in lemons and oranges. After holding lemons at —7° C for

The Lemon Fruit

48 8000

t 7000 D

au. o ta

/

6000

m

a

i

5000

iM

a a

t" (D 4000 U CO V)

/

z zoi < a

/

/

£ 2000 (A

30

/

/ /

/

/

/

/

/

/

/

/

/

/

/

/

/

f

t

/

j

'

/

t

W 3000

Id a u. o it 1000

/I /

/

/

/

/

t

/

/

*

y

/ V

/

. / r

/ j f

/ /

/

*

y

Y

/

y

40

50 60 TEMPERATURE, F

70

80

Fig. 9. Heat of respiration of citrus fruit. The curve for "Oranges" is for navel oranges which respire much more rapidly than Valencia oranges. (From Hendrickson and MacRill, 1948.)

1, 2, 4, and 6 hours and subsequently storing them at 20° C, the rate of respiration in the four lots increased 80,136,112 and 179 per cent, respectively. Navel and Valencia oranges responded similarly.

Composition and Physiology In studying the respiration of orange tissues by the Warburg technique, Hussein (1944) has shown that the relative amounts of oxygen absorbed by the different tissues are in the following descending order: flavedo, albedo, juice sacs, and carpellary membranes. The flavedo yielded the highest activity at a pH 5.0. From the effects of inhibitors and numerous added substrates it was concluded that a system involving cytochrome oxidase was responsible for most of the oxygen uptake. Although Hussein obtained his published data from oranges, he found that the results with lemon flavedo were similar. Haller, Rose, Lutz and Harding (1945) found: (a) that the heat of respiration of one ton of lemons equalled only 633 Btu per day when stored at 32° F, but equalled 12,669 Btu when stored at 100° F ; (b) dark green lemons (mature) respired as much as 9.1 times as rapidly as light green lemons, that is, as the maturity increased the rate of respiration decreased; (c) the rate of respiration of lemons from a given grove varied from year to year; (d) the relative rates of respiration of peel and pulp were approximately in proportion to their respective fresh weights; and (e) small sizes respired more rapidly than large sizes because they had a larger total surface per unit of weight. Harvey and Rygg (1936a) also found a higher rate of respiration in immature than in mature fruit. Balls (1947) states that a conservative figure for the rate of respiration of green lemons stored at 40° F is about 7 mg of CO2 per kilo per hour, or well over 1 gm of CO2 per week. Balls also confirmed the results of previous workers who have shown that bruising or rough handling of fruits materially increases their rate of respiration. For example, he found that when mature lemons were peeled, the rate of respiration of the peel alone was 4.6 times greater than the rate of the entire fruit before peeling. The following year Rubin, et al. ( 1 9 4 8 ) , obtained similar results. Mechanical disturbance (cutting) accompanied by active aeration, caused a 600 per cent increase in the rate of respiration in the albedo of the lemon peel. In tangerine albedo, respiration

The Lemon Fruit

Fig. 10. Lemons after 4 months in storage: Above, fruit with green button and no decay; below, fruit with black ( d e a d ) button and internal alternaria decay. (From Stewart, 1948.)

activation amounted to only 2 0 - 2 5 per cent. Orange peel gave intermediate results. Under their conditions these workers found that respiration activation was more pronounced in the albedo than in the flavedo. Harvey ( 1 9 4 6 ) found that when lemon fruits were placed in a

Composition and Physiology specially constructed sealed container with a manometer attached (see Harvey and Rygg, 1936a), he could measure the negative and positive pressure changes as the type of respiration of the fruit altered from approximately normal to anaerobic. These pressure changes were translated into terms of fruit vitality. The longer the duration and the greater the negative pressure, the greater the vitality and the longer the storage life of the fruit. Stewart (1948), with the assistance of R. D. Nedvidek and J. L. Baker of the California Fruit Growers Exchange, has found that the storage life of lemons, as well as of oranges and grapefruit, can be materially lengthened by the application of 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid). Both of these compounds were applied to the fruit while still on the tree in the form of a spray. The spray was found to be effective even when applied as long as five or six months before harvest. In the packinghouse the 2,4-D was applied to the fruit (not previously treated in the field) in a lanolin emulsion, in the waxing solution, or as a vapor. In both cases it was found that the normal vitality of the treated fruit was maintained over a much longer period of time than that of the nontreated fruit, as shown by the marked reduction in the number of black (dead) buttons (50 to 100 per cent) and in the amount of both surface and internal decay (40 to 80 per cent). The condition of the button is usually a good indication of the vitality of the fruit. Figure 10 shows a longitudinal section of a lemon fruit with a green button, and in a healthy condition. It also shows a similar section of a lemon fruit with a dead button, and internal decay (alternaria rot). Figures 11 and 12 further illustrate the marked effectiveness of 2,4-D and 2,4,5-T in controlling alternaria rot and black button on lemons while in storage. Figure 11 indicates, however, that the 1000 ppm of both 2,4-D and 2,4,5-T was too strong. It apparently injured the fruits to the extent that they became more susceptible to alternaria. Figure 12 also indicates that 1000 ppm of both substances was at least slightly beyond the proper

The Lemon Fruit strength for maximum control of black button. None of these fruits had been previously treated in the field. Biale and Young (1947) concluded from the results of their work that the rate of respiration of standard green lemon fruits

3. UJ

o

a. UJ 1

IN

Oi

00 Tp

Oi

0 00

IM

IM

IM

S

s

Oi Oi 1—1

0 IM

« • s

S O «

0 3 .ÏÏ «2 3 w

Ei Ä

IM CO to

0 io

Oi IO >0

co co IO

Oi IO IO

Oi co co

0 00 Tp

IM TP

s TP

00 00 IO

0 IO TP

0

0

0

0

0

0

0

0

0

0

0

IM

IM IM

10 TP IM

IO co IM

IO TP IM

0 co

IM Oi

f - 0 to I 1—1

co

TP TP

00

O

O

0

0

0

0

0

0

0

0

0

co IN

•cf

0 00

00

IM 00

IO co

8

IO to

0 10

IM io

§

co TP

TP TP

CO TP

co TP

co

00 co

0 Tf

Oi co

0 TP

Tp

0 TP

0

00 TP

IN CO

IO >0

02 IO

>0

IO

IO

10

•O

CD

00 TP

co co

Oi >0

00

00

00

00

T3 O t . X b V y-« o ë

02

jj

co

a o 8

Q «

5 s

0 5

H «

CO Jb O

£ H

* >,

s

TS Si

n P j

ij
s

S. s

o

o « o o

So




co

00

CD oo t— t—

t -

Totali (per cent)

o a

r00 0 0 0 0 00 OS

00

X 0 0 ) © 0 )

OS

1

'o

CO

a a .2 '3 "c3 V M ed

OS OS OS OS Ç

os

00 00 00 0 0 00

00

in a u»

ti 0 3

1 O O

Ca (per cent)

a> rt V

0 0 00 0 0 00 0 0

.S

«

CO

„ a

a ai 3 3 "o CO

0 8 " s 3

t - t - 00

t » 00 0 0 00 00

Total CO2 in A.I.S. (per ceni

Totali (per cent)

1 1

00

0 c J£ "E

§

cn

o 00 00 0 0 0 0 00

00

00 0 0 00 00 00

00

s í r- © O^ ° 8.8.1

Ss o m «


o o to r Tt< TP

co IM to Tf

02

H O < H Z H O « Ö * n 9B

e

•a S S a í d E » o ©si?

m fe * o S H^

P S


00 >o

w w

£ a a T3 S S Û. ® S «.2.2 •.2 £8

o C

«) or® * ^ ho £8=8

£ < a j 03 &

o e3 s53 o L.OJ

m

o

£

—I o -H (M dH Cfl

í 6 8.2

o

ce ÍS J 03 P á ta fc HH

á 02

S

e e s ¿-o 8.2 5 ® s l l l l i

¡z o s

8 H

¡o

fc ¡3 °""0>W ® U-O L. PL,

"tí

N

00 00 00 OO

a ®

s f e i (5-8=3

N

CO 00 00

i-i

eo

Composition and Physiology

• 107

Norris ( 1 9 2 6 ) states that the pectic substances which occur naturally in orange juice are essentially the same as those extracted artificially from the cell walls by chemical means. The pectins in the juices are derived from the cell walls by action of the acids and enzymes which naturally occur in the juice. This view is supported by the observation that the quantity of pectic substances in the juice was considerably increased when the fruit was macerated and left for 24 hours before expressing the juice, thus allowing the acids and enzymes to come in contact with the cell walls. Norman ( 1 9 2 8 ) appears to have been the only investigator in this country who has published the results of studies on the quantity and quality of pectin in the juice only of the lemon. He found that the mean yield of calcium pectate amounted to 76.3 per cent (ash-free basis) of the purified alcoholic precipitate. The mean methoxyl content of the pectin in the juice was 11.48 per cent which is very close to 11.76 per cent, the calculated value for tetramethoxyl pectic acid. He concludes that the soluble pectin as it exists in lemon juice is practically completely esterified, as it is in the cell wall. Of course, the values presented by Norman indicate only indirectly what percentage of the juice was pectin. An important physiological function of pectin in the lemon and other citrus fruits is the part which it plays in water absorption and translocation. Bartholomew ( 1 9 2 6 ) has shown that there are marked diurnal fluctuations in water content during growth and maturity of lemon fruits, especially under periods of stress in the summertime (fig. 6 ) . These fluctuations call for a rapid transfer of water. As has been mentioned previously, the structure of citrus fruits presents certain unique problems pertaining to water absorption and conductance because the fibrovascular system is mainly restricted to the albedo of the peel. Even in the albedo the majority of the cells are relatively far from the vascular bundles. For this reason the rate of water conduction would be very slow if it had to depend on its passage from cell to cell osmotically. Reed and Bartholomew ( 1 9 2 7 ) , Reed ( 1 9 3 0 ) , and

108 •

The Lemon Fruit

Bartholomew and Reed (1943) have advanced the theory that in these tissues the translocation of liquids depends largely upon their passage through the relatively thick layers of pectic sub-

between the cells. (From Bartholomew and Reed, 1943.)

stances between the cells (fig. 19), rather than through the cells. This view is supported by Tupper-Carey and Priestley (1923) who worked with very young tissues, in which the vascular system had not yet developed, and by Gaddum (1934) who worked with citrus fruits.

Composition and Physiology

• 109

Pectic substances are concerned also in the process of abnormal pathogenic and physiological formation of gum in tissues. Bartholomew ( 1 9 2 8 ) , who worked with the lemon, found that although other substances, such as starch and cellulose, contributed to gum formation, the pectic materials in the middle lamella appeared to be the first to be affected. A recent publication by Esau (1948) gives a good bibliography of articles on gum formation in the tissues of citrus and other plants.

Cellulose and Hemicellulose The literature appears to contain no references concerning the determination of the actual amounts of cellulose and hemicelluloses in the California lemon. Sucharipa ( 1 9 2 4 ) , working at the Czech University at Prague, found 15.00 per cent free cellulose and 8.94 per cent hydrolyzed cellulose in the albedo of lemon peel. Bartholomew and Robbins (1926) determined the total polysaccharides in the albedo of the peel but did not isolate and determine the amounts of cellulose and hemicellulose. Recently, Sinclair and Crandall (1949) determined by differences the total amounts of cellulosic material in the whole peel and peel albedo of mature lemons, some of which were green in color and some tree ripe (table 2 1 ) . After extracting the pectins from the alcohol-insoluble solids, the material that remained was designated as the cellulose-hemicellulose residue. The values presented in the table for cellulose and hemicellulose are, however, somewhat high. They include certain amounts of other substances such as firmly bound pectin, uronic acids and probably a very small amount of lignocellulose. This is shown by the fact that after extracting the pectin from the alcohol-insoluble residues, all samples tested yielded carbon dioxide (table 2 1 ) . The percentages of the cellulose-hemicellulose residues in the different samples of whole peel and albedo varied according to the methods used to extract the pectin (table 2 1 ) . After extracting

TABLE

21

RESIDUE AFTER EXTRACTION OF PECTIN FROM ALCOHOL-INSOLUBLE SOLIDS OF LEMON PEEL* Residue! Method of pectin extraction

H 2 0 + NH 4 citrate + NH 4 OH

H 2 0 + N H 4 citrate

Experiment no. and materialf

(1) Mature peel. . . (2) Mature peel. . . (3) Green albedo..

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

Mature peel. . . Green p e e l . . . . Green p e e l . . . . Green albedo.. Green albedo.. Mature albedo Mature albedo Mature albedo Mature albedo M a t u r e albedo Mature albedo Mature albedo M a t u r e albedo M a t u r e albedo

Mean H 2 0 + t a r t a r i c acid

(1) (2) (3) (4) (5) (6)

Mature albedo Green albedo.. Green albedo.. Green albedo.. Green albedo.. Green albedo..

Mean. .*. H 2 0 + t a r t a r i c acid + NH 4 OH

(1) Green albedo.. (2) Green albedo..

Mean

33.42 35.32 36.96

¿'33

35.23

0.33

40.93 44.16 43.06 46.91 45.98 42.82 43.64 47.98 46.20 41.82 44.54 42.70 46.08 48.04

i '25 1.25 1.10 0.90 0.95 1.00 1.34 1.01 0.74 0.84 0.85 1.09 1.37

6^58 6.45 6.35 5.73 6.32 6.42

44.63

1.05

6.31

36.66 41.36 44.00 43.40 39.40 41.20

1.12 1.41

5.22

41.00

1.27

5.22

32.26 37.82 35.04

Mean H 2 0 + HC1 + N H 4 citrate

Cellulose and hemi- Carbon Furfural cellulose dioxide fraction (per cent) (per cent) (per cent)

(1) (2) (3) (4) (5) (6) (7) (8)

Mature Mature Mature Mature Mature Mature Mature Mature

albedo albedo albedo albedo albedo albedo albedo albedo

36.60 36.20 34.32 33.24 32.10 31.60 28.46 28.72

0.77 0.77 0.78 0.69 0.65 0.60 0.65 0.69

32.65

0.70

• From Sinclair and Crandall, 1949. t The term "green" refers to color of peel; the fruits were commercially mature. | Values expressed as percentages of the alcohol-insoluble solids.

Composition and Physiology

• 111

the pectin from the peel or albedo with successive applications of hot water, ammonium citrate and dilute ammonium hydroxide, the residue remaining was much smaller (a mean of 35.23 per cent) than the amount of residue remaining when the final extraction with ammonium hydroxide was omitted (a mean of 44.63 per cent). Besides a small amount of additional pectin, the ammonium hydroxide extracted a portion of the hemicelluloses. A considerable part of the hemicelluloses was dissolved also by water and tartaric acid, leaving, after this treatment, a mean total residue of 41.00 per cent. The residue remaining after the water, ammonium citrate and ammonium hydroxide extractions (35.23 per cent) was about the same as after the water, tartaric acid, and ammonium hydroxide extractions (35.04). The mean of the residues remaining after extraction with water, hydrochloric acid and ammonium citrate was 32.65 per cent. When the results of any one method of extraction are compared, it is seen that there was relatively little difference between the values for whole peel and albedo only and between the values for green and tree-ripe peel. Further study of the combined cellulose and hemicellulose fraction was made by hydrolyzing it with 2 per cent hydrochloric acid under a reflux condenser. The results of these experiments are shown in table 22. To compare these data with those of other tables (9, 10, 14, 15), the values are reported as percentages of the alcohol-insoluble solids. The fraction of the alcohol-insoluble solids accounted for is the sum of the total pectin extracted as calcium pectate (34.85 and 40.58 per cent) and the residue after pectin extraction (30.79 and 31.20 per cent). This means that the determined fraction of the alcohol-insoluble solids was correspondingly lower for the green-colored peel (65.64 per cent) than for the tree-ripe peel (71.78 per cent). The values reported for the undetermined fractions (34.36 and 28.22 per cent) represent the nonpectinous materials (some of the hemicelluloses) that were extracted by the chemical reagents along with the pectin. After the extraction of the pectin,

tê

.5 « « u sï § scj So •O 8 oS &

M ^H IO CO co

¡S H ü « H Ph N

X H

»o

o J H H

PH

z O S «

J3 e l l f l «•Í3 S >i a

1-4

K

Í5 O

« a m < H

^

PH V fn < o J & J J H t> S

H w o S!

S IH oO S© I-« I I

Ë « .2 a

a" ö

Bí

.s a SS

Ss ® 8

Si

o o,

O"

á l f

O •J (3 •J hJ H O

a

3

fe*«

S

•s - s a ••fia O 2 *JH«-

•J o

a

o ¡x M

H PÍ

•J O Tí « G a l a i "Stì.23 H äü

>o on uo •a Tfl o co

M» O O -O *a g

4? o o | i p' 9 "o 8 £"2'Y »? B — J3 •P« Ï¡ 9o 5 « 0-3 2 •3 3 S-2 g OT i s . "» C a &-S S, 5 1 Ï S 'S

a fa

o> 5 £ « o S

G ®

«i ^ -g ®

Composition and Physiology

• 113

the amounts of residue (the cellulose-hemicellulose fraction) were approximately the same for both samples, 30.79 and 31.20 per cent, respectively. When the cellulose-hemicellulose fractions were hydrolyzed with 2 per cent hydrochloric acid, insoluble residues remained that amounted to approximately 20 per cent of the alcoholinsoluble solids. The fraction which was insoluble in 2 per cent hydrochloric acid was almost completely dissolved at room temperature in a solution of zinc chloride-hydrochloric acid, a solvent for cellulose. There remained, however, a small quantity of brown sediment (less than 0.5 per cent by weight) which was insoluble, probably lignocellulose. The total amounts of material hydrolyzed by the 2 per cent hydrochloric acid were 10.19 and 10.57 per cent, respectively, for the two samples. Approximately 68 per cent of the hydrolyzed material, or an average of 7.03 per cent of the alcohol-insoluble solids was determined as glucose. The nonreducing substances extracted with 2 per cent hydrochloric acid amounted, on the average, to 3.35 per cent, or approximately 32 per cent of the alcohol-insoluble solids. The results reported (table 22) do not reveal all the information that is desired concerning the cellulose-hemicellulose fraction. The results do show, however, that the nonpectinous fraction of the alcohol-insoluble solids of the lemon albedo is composed chiefly of a hemicellulose fraction which can be hydrolyzed with dilute hydrochloric acid, and a more resistant fraction which is almost completely soluble in cellulose solvent.

Proteins The protein content of the different parts of the mature lemon fruit is relatively low, except in the seeds. Proteins in whole fruit (minus seeds).—Colby and Dyer (18916) found the whole lemon fruit to contain from 0.128 to

The Lemon Fruit

114 •

0.172 per cent total nitrogen, and Colby (1894) found an average of 0.152 per cent total nitrogen for the years 1891, 1892, and 1893, inclusive. TABLE

23

NITROGEN IN WHOLE LEMON PEEL AND ALBEDO ONLY Nitrogen Sample no., f r u i t color, a n d material*

Per cent P e r cent A.I.S. dry weight

Soluble in 80 per cent alcohol t P e r cent P e r cent d r y weight of total

1. S i l v e r f r u i t : W h o l e peel

0.98 0.90

0.51

1.07

0.64

0.89

0.58

0.71

0.37

0.47

47.96

0.44

40.74

0.34

36.96

0.42

53.16

0.34

42.50

0.44

52.38

2. M a t u r e s t o r e d f r u i t : 1.08

Whole peel

3. T r e e - r i p e fruit: 0.92

Albedo only

4. G r e e n fruit: 0.79

Albedo only

5. G r e e n fruit: 0.80

Albedo only 0.84

0.46

0.73

0.40

6. G r e e n f r u i t : 0.84

Albedo only

* All f r u i t s were commercially m a t u r e a n d all were freshly picked except those of Bample no. 2 t Includes n i t r a t e nitrogen.

Mead and Guilbert (1927) found 6.39 per cent of crude protein in dried lemon press cake composed of peel, pulp, and seeds. Cameron, Appleman and Bialoglowski (1935) found the total nitrogen content per whole lemon fruit to gradually increase from about 0.02 gms in July to 0.20 gms in February, when the

Composition and Physiology

• 115

fruit had reached commercial maturity. Until early autumn the peel contained more than half of the total nitrogen of the whole fruit, but after that period the pulp contained more than the peel. Proteins in peel.—Recently, Sinclair and Crandall (unpublished) determined the total nitrogen content of both alcoholinsoluble and alcohol-soluble fractions of the whole peel and of the albedo only (table 23). The data in table 23 show that there was very little nitrogenous material in the lemon peel, a total nitrogen content of only 0.80 to 1.08 per cent, on a dry-weight basis. Since the alcohol-soluble substances had been removed, the amounts of nitrogen obtained from the alcohol-insoluble fractions are measures of the protein nitrogen of the whole peel (0.51 to 0.64 per cent) and of the albedo (0.37 to 0.58 per cent). Protein material was extracted from the alcohol-insoluble solids of lemon peel with either dilute (N/10)HC1 or KOH in alcohol. The protein can be precipitated from acid or aqueous solution with trichloroacetic acid or by regulating the extracts to pH 5.7. The crude protein had 13.85 per cent total nitrogen and an isoelectric point of pH 5.7. Approximately 50 per cent of the protein nitrogen of the alcohol-insoluble solids could be extracted with 5 per cent K2SO4. In general, a little less than half of the total nitrogenous material of the whole peel and albedo only (36.96 to 53.16 per cent of the total nitrogen) was soluble in 80 per cent alcohol. The soluble nitrogen came from the amid, basic and nitrate nitrogen and from the a-amino acids and peptids. The nitrate nitrogen amounted to only 0.08 per cent of the dry weights of the whole peel and of the albedo. Proteins in edible portion.—Chatfield and McLaughlin (1928) report 0.6 to 1.1 per cent, or an average of 0.9 per cent, total protein (N x 6.25) in the edible portion (tissues plus juice) of the lemon. The present authors (unpublished data) have recently found the total nitrogen content of the edible portion of the lemon fruit to range from 0.10 to 0.15 per cent of its fresh weight.

116 •

The Lemon Fruit

The protein of lemon pulp is similar to that of the orange in many of its chemical properties. It is insoluble in weak acids, neutral salt solutions and alcohol, but soluble in aqueous or alcoholic (95 per cent) solutions of dilute alkalies. The fact that lemon protein has these properties and that it remains in the alcohol-insoluble residue of the pulp is evidence that it is a component of the plastids, nuclei and other protoplasmic constituents of the segment membranes and juice vesicles and not of the juice itself. The isoelectric point (point of minimum solubility) of the crude protein of lemon pulp is approximately pH 5.5, and, as in the orange (Smith, 1925; Sinclair, Bartholomew, and Nedvidek, 1935), it exists in the solid state. This is demonstrated by the fact that the protein is soluble in alkali and is precipitated at pH 5.5 while the pH of the juice is approximately 2.2. The protein of lemon pulp contained 14.56 per cent nitrogen on an ash and moisture free basis. The amount of basic nitrogen was 24.00 ± 0.50 per cent of the total nitrogen. These values may vary. They depend on the amounts and kinds of impurities in the crude protein. As the total nitrogen of lemon pulp is very low (0.10 to 0.15 per cent of fresh weight), the protein content is correspondingly low. In addition to the protein nitrogen, the total nitrogen of the pulp includes the amino acids and other nitrogenous substances in solution in the juice. Even three precipitations with a 0.3 per cent solution of NaOH did not entirely free the protein of all carbohydrates. Owing to the carbohydrate contamination, the protein must be considered to be a crude product until physical measurements are made to establish criteria of purity. Proteins in juice.—The California Fruit Growers Exchange (1946) found an average of 0.6 gms of protein per 100 gms of fresh juice. Proteins in seeds.—In South Africa, de Villiers (1931) found 17 per cent of the dry weight of pressed lemon seed cake to consist of protein. Cook et al. (1946) report 21.6 per cent crude pro-

Composition and Physiology

• 117

tein in pressed citrus seed cake but do not specify the variety of citrus from which the seeds were taken. It is probable that the protein in citrus seeds is composed chiefly of globulins (Saunders, 1931).

Glutathione An important contribution to our knowledge of the mechanism of oxidation in plant and animal cells was furnished by Hopkins (1921) when he discovered and isolated a substance to which he gave the name "glutathione." He considered it to be a dipeptid composed of glutamic acid and cysteine. Later work, however, has shown it to be a tripeptid consisting of glutamic acid, glycine and cysteine. It can act as a hydrogen acceptor or a hydrogen donator, depending on whether it is in the oxidized or reduced form. Since Hopkins' work, glutathione has been found to be so widely distributed that at present it is considered to be present in at least most living plant and animal cells. Turrell (1950) appears to have been the first to detect the presence of glutathione in citrus fruit tissues, chiefly in the peel tissues of the lemon fruit. The glutathione content of the peel of healthy lemons was determined during his study of the injurious effects of elemental sulphur when applied to the surface of the fruit as an insecticide or fungicide (tables 24 and 25). All values are expressed on a fresh weight basis. The glutathione content of the peels of freshly picked untreated lemons, determined on the basis of the H2S produced, ranged from 8.9 to 56.8 mg per 100 gms of peel (table 2 4 ) ; when determined on its reaction with cadmium lactate, the amounts ranged from 16.02 to 43.60 mg per 100 gms (table 25). In the peel of similar untreated lemons that had been incubated in tightly sealed jars at 140° F for three to five hours the values ranged from 66.84 to 72.11 mg per 100 gms (table 25).

The Lemon Fruit

118 • TABLE GLUTATHIONE

(GSH)

24

CONTENT AND p H

OF P E E L OP

F R E S H L Y PICKED R I P E E U B E K A L E M O N S * Average G S H in peelf (fresh-weight basis)

Acidity of extract (pH)

2

mg/100 gm 56.8

6.84

4

40.9

6.62

4

35.5

7.17

4

24.1

6.80

4

8.9

6.94

4

16.1

6.82

4

24.4

6.81

Average

29.5

6.83

Number of samples assayed

* Adapted from Turrell, I960, t Determined by the Guthrie (1938) method. TABLE

25

GLUTATHIONE ( G S H ) CONTENT OF P E E L OF NONDUSTED AND S U L F U R - D U S T E D E U R E K A LEMONS INCUBATED IN TIGHTLY SEALED J A R S AT 140° F * F

(Fresh-weight basis)

Sampling date

Oct. 4 to 12, 1945 Oct. 16 to Nov. 19, 1945 Nov. 20 to Dec. 7, 1 9 4 5 Dec. 10, 1945, to Jan. 9, 1 9 4 6 . . . . Jan. 11 to 18, 1946

Number of samples

7 62

GSH in peel of nonincubated, nondusted fruit mg/100 gm 24.05 16.02

G S H in peel of incubated fruit Incubation period hours 0

Nondusted

S-dusted

mg/100 gm mg/100 gm

0 3

66.84

82.04

9

43.60 40.22

4

72.11

84.93

4

36.68

5

68.12

85.56

7

• From Turrell, 1950. t Determined by the cadmium lactate method of Binet and Weller, 1934.

It is of interest also to note in table 25 that the application of elemental sulphur to the surface of the fruits before incubation in tightly sealed jars, caused an increase in the total glutathione content in the peel. The range in these fruits was 82.04 to 85.56 mg per 100 gms of peel. The increase was thought to be due to the conversion of oxidized glutathione to the reduced form by the H 2 S formed by the applied sulphur.

• 119

Composition a n d Physiology

Enzymes Biological reactions are not caused by a single enzyme but by a multitude of enzymes which produce a progressive series of reactions until a substance, for example starch, is formed from CO2 and H2O or is changed back to CO2 and H2O. Internal or external conditions may cause the reactions to stop at any point and intermediate products may accumulate. The lemon fruit, in common with the tissues of many other plants, contains many enzymes such as amylase, invertase, zymase, lipase, and protease. The comments in the following paragraphs in this section are confined, however, to some of the more recently discussed enzymes which have been found in citrus fruits. Reed (1914) detected peroxidase in the walls of the juice vesicles; Onslow (1920) and Willimott and Wokes (1926) found peroxidase in the peel; and Ajon (1926) reports the finding of not only peroxidase but also oxidase and catalase rather generally distributed throughout most of the fruit tissues. All of these determinations appear to have been qualitative. Davis (1942) appears to have been the first to determine quantitatively the amounts of peroxidase in the different tissues of the flesh and seeds of citrus fruits. The following tabulated data show the distribution and quantities of peroxidase found in the different tissues of the flesh and seeds of citrus fruits. Peroxidase (Expressed

units per kilo of fresh tissuet in Balls and Hale units, 1933)

Navel orange Fruit tissues: Albedo 5.5 Flavedo, inner . . . . 14.0 Flavedo, outer . . . . 31.3 Endocarp 1.7 Sediment from juice 1.8 * Peel

Marsh grapefruit

13.8 *

350-414 14.6 0.7 *

Lemon

2.8 *

195.5 4.6

Tangerine *

*

* *

*

*

*

58.8

(Continued

on next

page)

120 • ( Continued

The Lemon Fruit from preceding

page)

Seed tissue: Whole seed . . . . Seed coat, inner Seed coat, outer Cotyledons . . . .

52.2

t From Davis, 1942. * No analysis made.

Miller and Schomer (1939) and Miller (1946) report the presence of reductase in lemon peel as measured by the time, in minutes, that it took an aqueous extract to reduce potassium permanganate. Although reducing sugars and acetaldehydes might have caused part of the reduction, that the reaction was probably enzymatic was shown by the fact that the ability to reduce potassium permanganate at different rates was destroyed by boiling the peel. These workers found that reductase activity in the peel of mature lemons stored at 32°, 3 6 ° , and 4 0 ° F was consistently lower than in the peel of those stored at 50° and 6 0 ° F. Joslyn and Sedky ( 1 9 4 0 ) studied the activity of the pectic enzymes in citrus fruits by observing the rate of decomposition of pectin in macerated tissues under various conditions. The rate of hydrolysis of the natural pectins was more rapid in oranges than in grapefruit, and slowest in the lemon. In the three fruits, the amount hydrolyzed approached the maximum at the end of 24 hours, diminished rapidly during the next two days and finally hydrolysis ceased. The maximum decomposition of the pectins occurred at pH 3.5 for oranges, and at pH 4.5 for both grapefruit and lemons. According to Kertesz ( 1 9 3 6 ) , pectinase is composed of a group of enzymes capable of hydrolyzing pectin and pectic acid to reducing sugars and other substances. The enzyme responsible for the hydrolysis of polygalacturonic acid was designated as polygalacturonase. According to Jansen and MacDonnell ( 1 9 4 5 ) , this enzyme is distinctive in that it has only slight action on the completely esterified pectins.

Composition and Physiology

• 121

The enzyme that hydrolyzes the methyl esters of pectin has been called pectin methoxylase by Kertesz (1936) and pectin esterase by Lineweaver and Ballou (1945). With respect to citrus fruits, MacDonnell, Jansen and Lineweaver (1945) state that pectin esterase occurs in relative abundance in the navel orange, grapefruit and lemon, but that there is less in the lemon than in the two other fruits. Its activity per gram of wet weight was higher in the flavedo than in either the albedo or juice sac tissues. Both albedo and juice sac tissues, minus juice, had an activity equivalent to about half that of the flavedo. The activity was confined primarily to the tissues themselves rather than to their juices, as shown by the fact that the sap from the flavedo and filtered pulp juice manifested little or no activity. The pectin esterase activity of citrus peel flavedo can produce the de-esterification of pectin at 50 per cent of the maximum activity throughout the pH range of 4.0 to 9.0, with the proper control of the cation concentration. In their discussion of "The newer knowledge of pectic enzymes," PhafiE and Joslyn (1947) divide pectic enzymes into two groups: "pectin esterase" which catalyzes the hydrolytic removal of methyl alcohol from the pectin molecule (synonyms: pectase, pectin-methyloxylase, pectin methylesterase), and "polygalacturonase" which catalyzes the glycosidic hydrolysis of polygalacturonic acid into monogalacturonic acid (synonyms: polygalacturonidase, pectinase, pectolase, pectin polygalacturonase). They state that pectin esterase occurs in various plant tissues more or less free of polygalacturonase, but that polygalacturonase (from fungi or bacteria) appears always to be accompanied by pectin esterase. Pectin esterase was first discovered by Fremy (1840) and polygalacturonase by Bourquelot and Herissey (1898). Recently Axelrod (1947) discovered the enzyme phosphatase in both tissues and juice of citrus fruits (oranges, lemons and grapefruit). This was not only the first time that phosphatase had been found in citrus fruit, but is said to be the first time that an

The Lemon Fruit

122 •

enzyme had been reported as being present in citrus juices. The phosphatase was found to be capable of hydrolyzing a variety of phosphate compounds, including phosphomonoesters, but not phosphodiesters. The enzyme was concentrated and partially purified. Such information will help to reveal the nature of the carbohydrate metabolism that occurs in citrus fruit during maturation and while in storage. Another previously uncharacterized enzyme occurring in oranges, grapefruit, and lemons has been isolated recently by Jansen, Jang, and MacDonnell ( 1 9 4 7 ) . Since it was most active in hydrolyzing esters of acetic acid, it was named acetylesterase. All aliphatic esters of acetic acid are hydrolyzed by the enzyme, whereas N-acetyl compounds and acetylphosphate are not hydrolyzed. The enzyme was found in greatest abundance in the flavedo and decreased progressively toward the center of the fruit. More was found in the orange and grapefruit than in the lemon. The pH optima for its action on acetins ranged from 5.5 to 6.5. Some evidence has been advanced which appears to indicate that ascorbinase (or vitamin C oxidase), at least to some extent, may be responsible for the destruction of ascorbic acid in lemon and other citrus juices (Huszak, 1937, Somogyi, 1 9 4 4 ) . These results, however, have been questioned by Hussein ( 1 9 4 4 ) . The so-called coagulating enzymes which are responsible for the curdling of stored lemon and grapefruit juices are probably the pectic enzymes. Glycosidase breaks the bond between the sugar and the other components of glycosides.

Vitamins Although it was suspected as early as the middle of the 18th century, the vital part that accessory food factors (vitamins) play in the life processes of plants and animals was not definitely recognized until after the beginning of the present cen-

Composition and Physiology

• 123

tury. Hopkins ( 1 9 0 6 ) appears to have been the first to prove that an "accessory food factor," in addition to the four main classes of food (carbohydrates, fats, proteins, and mineral salts), was essential for normal growth and health of the body. It is of interest to note, however, that although the existence of vitamins is now almost universally known, yet of those known today none had been isolated, crystallized and synthesized until 2 5 or 30 years ago. Citrus juices were the first observed accessory food factors or vitamins. In general, it may be said that plants synthesize their own vitamins while animals have to obtain them directly or indirectly from plants. Vitamins need to be present in only very small quantities to be able to perform their vital functions as energy transformers and metabolic regulators in the human body. Up to the present time, 23 vitamins have been identified and some 15 unidentified vitamins or factors are known. Lemons and other citrus fruits serve as an important source of some of the vitamins. In some instances the ascorbic acid content of lemons has been reported to be as high as 68 mg per 100 ml of juice or even higher, but this is above the general average. Data supplied by the Research Department of the California Fruit Growers Exchange (correspondence, 1949) lists as follows the kinds and typical amounts of vitamins that so far have been found in the juice of mature California lemons. Vitamin

Folic acid Thiamin ( B J . Riboflavin (B 2 ) Niacin

Typical values, Micrograms/100

expressed grams of

as: juice

1 60 60 135

Ascorbic acid (C) Inositol Flavonoids ( " P " )

The vitamin values cited above are the general averages of the results of many investigators. Tressler, Joslyn and Marsh (1939)

The Lemon Fruit

124 •

list vitamin A (probably in the form of its precursor, carotene) and vitamin G also as being present in " f a i r " amounts in lemons. As may be seen from the group of values presented, the amounts of different vitamins in the lemon vary greatly. Baier and Manchester (1949) have recently shown that although i-inositol is present in relatively large amounts in lemon juice (85 mg/100 gms juice) it is present in much greater quantities in the peel. For example, they found 3200 mg of inositol in 100 gms of dried lemon peel infusion (L.P.I.), a pharmaceutical preparation now being sold through drug channels. These authors also report that although lemon juice contains an appreciable amount of folic acid the pulp and especially the whole fruit are better sources for this vitamin. The amount of any given vitamin in a plant is usually governed by species, age and kind of tissue, and by seasonal and environmental factors. The vitamin content of individual fruits also may show considerable variation. For example, one lemon in a lot may contain at least 60 per cent more ascorbic acid than another lemon in the same lot. As an illustration of one of the influencing factors, the immediately following values, taken from Braverman (1949), show the seasonal variations in vitamin C content that were found to occur in the juice of Palestine lemons. The values were obtained by Dr. F. Stern of Jaf-Ora Ltd., Rehovot, and they represent the averages of the results obtained during three consecutive seasons. In the last column the "averages" represent the mean value of daily tests during the month. Mg/100 Month

December January.. February. March . . , April May

Vitamin C ml lemon

Min.

Max.

52.8

66.9

52.8 52.8

59.8 55.3

juice Average

60.54 70.05 61.95 58.08 54.03 57.70

Composition and Physiology

• 125

The data in table 26 show the effects of the following factors on the ascorbic acid content of lemon juice: (a) area in which fruit was grown, (b) color of fruit when picked, and (c) length of time fruit was kept in storage before tests were made. In every lot of fruit the ascorbic acid content of the juice was higher at the end of the storage period than at the beginning and, with one exception (No. 9 ) the longer the storage period for any one lot of fruit, the greater the increase in ascorbic acid. With three exceptions (Nos. 1, 5 and 6 ) the increase was greater in the juice from the « light-green and dark-green fruits than in that from the silver fruits. Attention is also called to the fact that at the end of the first storage period (10 or 11 weeks) the ascorbic acid content of the silvers in Nos. 1, 4 and 6, the dark greens in No. 3, and the light greens in No. 5 was the same or a little lower than had been found in the controls. Since all of the tests reported in table 26 but one were made within a period of less than two months, they do not show the possible effect of time of year in which the fruits were picked on the ascorbic acid content in their juice. The influence of this factor is indicated in the immediately preceding values quoted from Braverman (1949). Lemons are an especially good single source for ascorbic acid and "vitamin P " and much of the research interest has centered around these two vitamins. Giroud et al. (1936) state that with only a few exceptions, the highest ascorbic acid content is found in those tissues which contain the most chlorophyll and carotenoids. This probably explains why Bacharach, Cook and Smith (1934) found much more ascorbic acid in the flavedo than in the albedo of the lemon peel (210 mg and 46 mg, respectively, per 100 gms of flavedo and 100 gms of albedo). For a chronology of the discovery, isolation, crystallization, and synthesis of ascorbic acid and other known vitamins, see Rosenberg (1942). Isbell (1944) has worked out a method for synthesizing vitamin C from galacturonic acid. The source of his galacturonic

TABLE

26

ASCORBIC A C I D C O N T E N T OF J U I C E FROM L E M O N S STORED FOR DIFFERENT PERIODS* No., area, and pickirig date, 1949-50

Maximum increase, per cent

Ascorbic acid (mg/100 ml juice)

Color of fruit mg

mg

mg

mg

(ID 36 54 56

(16) 42

(27)

1. Fallbrook Dec. 15

Silver Light green... Dark green. . .

(0)t 36 50 52

2. Fallbrook Feb. 5

Silver Light green.. . Dark green. . .

(0) 50 53 50

(20) 59 62 61

3. Porterville Dec. 15

Silver Light green... Dark green. . .

(0) 64 60 56

(11) 67 62 56

(27) 70 66 64

4. Kaweah Dec. 15

Silver Light green.. . Dark green. . .

(0) 62 56 59

(11) 59 58 61

(19) 63 64

(27) 66 66 68

5. Arizona Dec. 20

Silver Light green... Dark green. . .

(0) 53 56 49

(11) 55 54 57

(16)

(26) 60 63

6. Upland Jan. 1

Silver Light green.. . Dark green. . .

(0) 48 52 52

(10) 48 53 58

(25) 61 60 65

7. Upland Feb.10

Silver Light green.. . Dark green. . .

(0) 55 50 65

(20) 69 70 85

8. San Fernando Jan.10

Silver Light green... Dark green. . .

(0) 48 42 43

(14)

9. Limoneira Feb. 1

Silver Light green.. . Dark green. . .

10. Limoneira April 15

Silver Light green... Dark green. . .

66 63

16.7 32.0 21.2 18.0 17.0 22.0

¿3

9.4 10.0 14.3 6.5 17.9 15.3 13.2 12.5 28.6

27.1 15.4 25.0 25.5 40.0 30.8

5Ì 51

(26) 60 58 58

25.0 38.1 34.9

(0) 58 54 59

(12) 62 62 65

(23) 63 59 66

8.6 14.8 11.9

(0) 53 58 62

(15) 62 67 78

17.0 15.5 25.8

* From Harlan E . Barber and E . M. Harvey, U . S . D . A . Bureau Plant Industry, Soils and Agricultural Engineering. Horticultural Field Laboratory, Pomona, California. (Unpublished data.) t Figures in ( ) at the head of each group of values show the number of weeks the different samples were kept in storage before juice determinations were made; (0) = controls, tests made as soon as fruits were picked.

Composition and Physiology

• 127

acid in this case was beet pulp, but if the same results can be obtained with citrus peel which is so rich in pectin, then vitamin C can be artificially synthesized in quantities about six times greater than the amount normally found in the peel. Lorenz and Arnold (1941) found 1.75 mg of crude citrin ("vitamin P " ) in each 100 gms of whole lemon fruit. The "vitamin P " complex, unlike vitamin C, is distributed more or less evenly through the juice and peel. According to Scarborough (1945), hesperidin and hesperitin cannot be called vitamins, but he suggests that they may be precursors of a more active substance, possibly the chalcone. As such, they, like carotene, could be considered to be provitamins. Higby (1943) arrived at the conclusion that hesperidin converted to a soluble derivative can function as "vitamin P . " He gives an historical review of the discovery, chemistry and medicinal use of "vitamin P . " More recently Clark (1947) has given a comprehensive discussion of the present status of "vitamin P . " By way of explanation, the term "vitamin P " is placed in quotation because no one has proved conclusively that the flavonoids are vitamin in nature. These compounds are, however, very useful therapeutic agents or "drugs." The Research Department of the California Fruit Growers Exchange (1945) has compiled a list of 387 references on the subject of "vitamin P." 1 Just how the six vitamins tabulated in the first part of this section function physiologically in plant tissues is only partially known at the present time. Because of their role as coenzymes or fragments of coenzymes, these and at least some of the other vitamins may be considered to be typical catalyzers of assimilation. The following are some of the more or less specific functions that have been ascribed to several of these vitamins: Folic acid, said to be essential in fat metabolism; thiamin (Bi), concerned with root growth and metabolism of carbohydrates; riboflavin (B2), 1 Since this manuscript was sent to the editors the Joint Committee on Biochemical Nomenclature of the American Society of Biological Chemists and the American Institute of Nutrition has recommended that the term "vitamin P " should no longer be used (Vickery, et al., 1950).

The Lemon Fruit

128 •

functioning as a hydrogen carrier in biological oxidation of glucose; ascorbic acid (C), important in oxidation-reduction and is so abundant in some tissues that it may act also as a nutrient and carbon reserve; inositol, which may serve as a growth-promoting substance and may be an intermediate product in the transformation of glucose into such sugars as ¿-ribose; and "vitamin P," which may act as a detoxifying agent, stored in the form of a glucoside (hesperidin). Recently Galston and Baker (1949) have shown that riboflavin (B2) is a photoreceptor in the destruction of auxin by visible light. Rosenberg (1942) and Schopfer (1943) give very good reviews of past work on vitamins and they need not be discussed in further detail here. Carroll (1943) gives a detailed discussion of possible functions of ascorbic acid in plants.

Inorganic Constituents Total ash.—The following values for the total ash content of different parts of the lemon fruit show considerable variation. This is not surprising when one considers that not only the rootstock and seasonal factors but the area in which grown may each or all exert an influence on the absorption and accumulation of salts. For example, it may be seen that the ash content of the peel from one area (4.94 per cent) was 65 per cent greater than that of the peel from another area (3.00 per cent). Portion of fruit, and investigator Whole fruit Colby ( 1 8 9 4 ) , 3-year average Haas and Klotz ( 1 9 3 5 ) Haas and Quayle ( 1 9 3 5 ) av. 3 determs

Total ash content % 0.54* 5.31 4.76

Peel Haas and Klotz ( 1 9 3 5 ) Stem half

3.75

Composition and Physiology

• 129 3.69 4.94 3.00

Stylar half Whole peel from different areas Sinclair and Crandall (unpublished) Pulp (minus seeds) Haas and Klotz (1935)

4.61

Juice Chatfield and McLaughlin (1928) Sinclair and Crandall (unpublished)

0.33* 3.10

* Percentage of fresh weight. All other values are on a dry-weight basis.

The California Fruit Growers Exchange ( 1 9 4 6 ) found 0 . 4 2 gram of total ash per 1 0 0 grams of fresh juice. Common elements.—The

early investigators who determined

the mineral content of California lemons reported values for the elements in the oxide form. These will not be reported here. Recent determinations have been limited but the following values will indicate, in general, the quantities of the more common inorganic constituents that may be found in the peel, pulp, and juice of the California lemon. Portion of fruit, and

Inorganic

investigator

Mg

Whole fruit Ca Haas and Quayle (1935) Areal 15.27 3.01 Area 2 13.90 2.59 Area 3, soil fairly saline 13.08 2.66 Peel Haas and Klotz (1935) Stem half Stylar half Whole peel (other samples) Sinclair and Crandall (unpublished) Whole peel

Na

constituents

K

CI

PO4

0.31 0.78 7.01

11.50 12.43 13.81

As per cent of ash

7.15 9.38 7.79

30.19 30.32 29.95

As per cent of dry matter

1.15 1.02

0.14 0.10

0.09 0.05

0.39 0.58

.. ..

0.15 0.19

1.26

0.13

0.18

0.92

..

0.28

0.78

0.06

0.06

..

0.18

0.68 (Continued

on next

page)

The Lemon Fruit

130 • (Continued from preceding Portion of fruit, and

page)

investigator

Pulp Haas and Klotz (1935) Seeds removed Juice (centrifuged) Sinclair and Crandall (unpublished)

Ca

Mg

Inorganic

Na

constituents

K

CI

PO

As per cent of dry matter

0.38

0.12

0.45

1.92

0.06

0.10

0.05

1.28

..

0.54

0.42

Anyone wishing to translate these dry-weight values into freshweight values can do so with reasonable accuracy by referring to the proper tables. Tables 9 and 12 (p. 62, 78) give the moisture content of lemon peel. Tables 3 and 8 (p. 14, 6 1 ) give solublesolids values for lemon juice. Therefore, the moisture content can be determined by subtracting these values from 100. The California Fruit Growers Exchange ( 1 9 4 6 ) found the following average amounts, in milligrams, of mineral elements in each 100 grams of fresh lemon juice: calcium 26.0, phosphorus 13.0, iron 0.35, potassium 164.0, sodium 21.0, magnesium 10.0, sulphur 7.0, chlorine 3.0. These figures represent the averages of carefully selected values as found in the literature, and are for freshly extracted beverage juice and not for juice that had been finely screened or centrifuged. Values obtained by individuals in different localities vary, as influenced by such factors as environmental conditions under which the fruit was grown, and the amounts of pulp tissues and plastids in the juice when the determinations were made. Calcium is especially abundant in the lemon peel because the peel contains more pectin than any other portion of the fruit. The calcium combines with the pectin to form calcium pectate. Because of this combination, not only in the peel but in the tissues of the pulp, the major portion of the calcium is in a water-insoluble form. Sinclair and Eny (1945) found that calcium as calcium oxalate is present also in relatively great abundance, especially in the mature peel. As the calcium oxalate accumulates, it forms beautiful monoclinic crystals, usually one crystal in a cell.

Composition and Physiology

• 131

Potassium was higher than any of the other inorganic constituents in both juice and pulp but sometimes not so high as calcium in the peel. Nearly all of the potassium in the fruit is present in a soluble form. The amounts of sodium and magnesium were usually the lowest in all parts of the fruit. The exceptionally high chlorine value obtained by Haas and Quayle in area 3, where the soil was fairly alkaline, is of interest. Since none of the cations reported was present in similarly high amounts the chlorine must have combined with hydrogen to form HC1 which would have made the tissues unusually high in acid. The stem half of the peel appears to have a slightly greater concentration of total ash and of calcium, magnesium, and sodium than the stylar half. The reverse is true for potassium and phosphate. These differences are probably not highly significant since they are expressed on a dry-weight basis. Haas (1948) has recently determined the effect of eleven different rootstocks on the accumulation of some of the inorganic constituents in the peel of the lemon. Only the averages of the high and low accumulations are given here. Figures in parentheses are the values expressed as percentages of dry matter. Calcium, high on sour orange and rough lemon ( 1 . 3 3 ) , low on sweet lemon and Bessie sweet orange ( 0 . 9 7 ) . Magnesium, high on rough lemon, sweet lemon and Sampson tangelo (0.14), low on C.E.S. 343 grapefruit and Duncan grapefruit ( 0 . 1 0 ) . Potassium, high on C.E.S. 343 grapefruit, Duncan grapefruit and Sampson tangelo (0.96), low on rough lemon and sweet lemon ( 0 . 5 0 ) . Phosphorus (total), high on Cleopatra mandarin, Duncan grapefruit and C.E.S. 343 grapefruit, 733 ppm.; low on Brazilian sour orange, Rubidoux sour orange, Bessie sweet orange, and sweet lemon, 583 ppm. There were some exceptions. For example, the fruit from a tree on a given rootstock might have a higher calcium content in one plot than in a nearby plot in the same grove, but the trends were as given.

The Lemon Fruit

132 •

Trace elements.—The following mineral nutrients have been isolated from lemon fruits in minute quantities. Iron.—Peterson and Elvehjem ( 1 9 2 8 ) , 7.5 mg in peel and 1.5 mg in juice, per kilo, fresh weight. Manganese.—McHargue ( 1 9 2 4 ) , 4.12 mg in peel and 3.38 mg in juice, per kilo, dry weight; Quartaroli ( 1 9 2 8 ) , 6.75 mg in peel, per kilo, dry weight trace in pulp and in seeds; Peterson and Skinner ( 1 9 3 1 ) , 3.6 mg per kilo in whole fruit, dry weight. Copper.—Quartaroli ( 1 9 2 8 ) , 3.12 mg in peel, 2.04 mg in pulp, and 12.20 mg per kilo in seeds, dry weight; Lindow, Elvehjem and Peterson ( 1 9 2 9 ) , 0.4 mg per kilo in pulp, fresh weight; Haas and Quayle ( 1 9 3 5 ) , 2.8 to 4.9 ppm in whole fruit, dry weight. Zinc.—Bertrand and Benzon ( 1 9 2 8 ) , 3.3 mg in pressed peel and residue, and 1.7 mg in juice, per kilo, fresh weight. Boron.—Haas ( 1 9 4 5 a ) , from five localities and at different times of year: peel, 22.5 to 34.5, and pulp, 11.7 to 27.6 ppm of dry matter. Haas ( 1 9 4 5 6 ) , in outer and inner peel as affected by rootstock: Rootstock

Bessie sweet orange Rough lemon

....

African sour

Alkaline ash of lemon juice.—Recently Sinclair and Crandall (unpublished) determined the alkalinity of the ash of the juice of freshly picked, mature yellow and green lemons and of lemons that had been in storage for about six weeks (table 2 7 ) . The 3.0 milliequivalents per 100 ml of juice from the freshly picked lemons, and 3.2 m.e./lOO ml of juice from the stored lemons (average values) are lower than the 4 milliequivalents per 100 ml reported by Sherman ( 1 9 4 6 ) . These values, however, are for centrifuged juice and not for the whole pulp or fresh beverage juice.

• 133

Composition and Physiology

The organic acids are present in citrus juices in two forms, namely, as free acids, which can be titrated with sodium hydroxide, and as combined acids, that is, acids in combination with the cations in the juice. T A B L E 27 ALKALINE ASH AND THE EQUIVALENT COMBINED ACID OF LEMON JUICE Sampling no. and variety

Sampling date

Color of fruit

Alkalinity of ash

Combined acid as citric

m.e./lOOml*

mg/100 ml

Freshly picked mature fruit from experimental 1. 2. 3. 4. 5. 6. 7. 8.

Lisbon Lisbon Lisbon Eureka Eureka Lisbon Eureka Lisbon

April April April April June June June June

3 9 10 20 8 12 18 25

Yellow Yellow Green Yellow Green Green Green Green

Mean Mature fruit from •packinghouse 9. 10. 11. 12. 13. 14. 15.

Eureka Eureka Eureka Eureka Eureka Eureka Eureka

Mean

April April April May May May May

23 25 30 2 7 10 14

Yellow Yellow Yellow Yellow Yellow Yellow Yellow

plots

2.8 3.4 2.9 3.0 2.9 2.9 2.8 2.9

179.2 217.6 185.6 192.0 185.6 185.6 179.2 185.6

3.0

188.8

storage 3.3 3.3 3.3 3.0 3.4 3.0 3.3

211.2 211.2 211.2 192.0 217.6 192.0 211.2

3 2

206.6

* As these determinations were made on centrifuged juice, the values are slightly lower than the approximate alkalizing capacity reported for lemon juice (4 m.e. per 100 gms) in the standard testa on human nutrition.

During the ashing process of citrus juices, the organic materials are burned off leaving the equivalent mineral elements (cations) as carbonates, oxides and some sulfates and phosphates (Sinclair and Eny, 1946a). The amount of standard acid required to neutralize this ash represents the alkalinity m.e. per

The Lemon Fruit

134 •

100 ml juice), and it is a fair measure of the cation content combined with the organic acids in the juice (table 2 7 ) . The specific cations combined with the organic acids have not been determined. It is highly probable, however, that the citrates (salts) are present in the juice as the potassium acid citrates, since the potassium concentration accounts for 60 to 70 per cent of the total cations of the ash. It is apparent that the amount of organic acids which combines with the cations to form salts depends upon the concentration of available cations. The amount of free organic acids available for salt formation in the juice is never a limiting factor, for the acid concentration at all times is many times greater than the total mineral content. Although the total mineral content of a given sample is obtained from the ash, the concentration in the juice is correlated with the mineral elements absorbed by the roots during fruit development. Environmental conditions favorable for increased absorption of minerals by the plant could produce an increase in the total ash of the fruit, thereby increasing the alkalinity of the ash in the juice.

Seeds The number of seeds in lemon fruits varies greatly. Bartholomew (1937) determined the number of seeds in several lots each of mature Eureka lemons from three different areas in southern California. Of the 465 fruits examined, 70.7 per cent contained an average of 2.4 fully developed seeds (range per fruit, 1 to 18) and an average of 2.0 undeveloped seeds. Of the remainder, 10.6 per cent contained undeveloped seeds only, and 18.7 per cent were entirely free of seeds. This study was undertaken for physiological reasons and the results showed that there was no relation between the presence or absence of seeds in the lemon and its susceptibility to "endoxerosis," a gumming and desiccation of the tissues in the peel and pulp.

Composition and Physiology

• 135

Other investigators have expressed the seed content of lemons as a percentage of the fresh weight of the fruit. This method is satisfactory for commercial purposes but has little physiological significance. Investigator

Colby and Dyer (1891a) Colby (1894), 3-year av., 1891-1893 Chatfield and McLaughlin (1928) . .

Seed content, per cent fruit wt.

0.1-0.2 0.6 0.2-0.7

Very little work has been done to determine the possible relation between the number of seeds in the fruit and the physiology of the fruit or tree. Fudge (1938) found that in seedy varieties of grapefruit the seeds accumulated such a large portion of the magnesium present in the tree system that the leaves were robbed and, as a result, they assumed a bronzed appearance. It is not impossible that a similar condition may exist in seedy lemon fruits with reference to magnesium or some of the other mineral food elements. De Villiers (1931) suggests that after most of the oil (30 to 35 per cent of dry wt. of seeds) has been expressed, the seed cake should be used as animal food because of its relatively high content of carbohydrates (43 per cent), proteins (17 per cent), fats (9 per cent) and mineral matter (4 per cent). Cook et al. (1946) report 21.6 per cent protein and 13.95 per cent crude fat from dressed seed cake but do not specify the citrus variety from which the seeds came.

Chapter III

PRODUCTS AND THEIR USES

^ ^ ^ ^ N L Y a very condensed resume of the data concerning lemon products ("by-products") is given. The majority of the products come from the tissues rather than from the juice of the fruit. In general, only those substances which apply or may apply to the lemon are mentioned. Because of trade secrets it is not always possible to state the amount of a product that is being produced currently. Most of the following information has been taken from the reports of Cook et al. (1946) and Joseph (1947). For the most recent discussion of citrus products see Braverman (1949). Figure 20 from Joseph shows at a glance the many products that are, or may be obtained from lemons, oranges and grapefruit. The chart gives a good general picture of the many products that are obtained from commercial citrus fruits, but as can be seen a few of the products listed are not obtained from the lemon. The same holds true for oranges and grapefruit. Two of the products that are obviously not obtained from the lemon are "orange molasses" and "naringin." While the lemon does not contain the flavonone naringin, it contains other flavonoid substances of commercial interest, such as "Calcium Flavonate, Lemon." In the chart these would come under "Vitamin P," and should replace the product called "Lemon Peel Extract." Under "Juice, Concentrate," the term "Bottler's Base" means a base for carbonated 136 •

Products and Their Uses

'137

beverages, and "Dairy Base" a base for noncarbonated or "still" beverages. About 75 lemon fruit products and product uses are listed on the following pages of this section.

Whole Fruit Disposal of 1,000 tons of waste pulp (orange, lemon and grapefruit) per day is a major problem for citrus products factories. As used here, the term "pulp" refers to both the peel after the oil has been removed, and to the edible portion of the fruit after the juice has been extracted. Stock feed.—The pulp is dried and fed as whole pulp, or is first ground into a meal. In both forms it is usually mixed with ground alfalfa or some other form of stock feed before being fed. The pulp is relatively high in carbohydrates, proteins, fats, and minerals. Mead and Guilbert (1927) state that at the time of their writing, 300 to 600 tons of dried lemon pulp were being produced annually in California. They found that over 81 per cent of the dry pulp was digestible. As would be expected, the amount of lemon pulp produced at the present time is far in excess of the amount produced in 1927. For example, one products factory in California produced about the same amount monthly in 1948 (300 to 600 tons) as was produced annually in 1927. Pectate pulp.—Pectate pulp is made in the same equipment as that used for drying the pulp that is to be used for stock feed. It is converted into a dispersion form that is used for certain kinds of steel quenching, for aiding latex creaming at rubber plantations, as an ingredient in oil-well drilling muds, for paper sizing, and as an antistick on paper containers. Pectic acid.—Pectic acid may be isolated from the pulp but it is usually isolated from previously prepared pectin. It is used as an acidulant in certain pharmaceutical powder mixtures to prevent the loss of capacity for effervescence.

138 •

The Lemon Fruit

Vitamin C.—At the present time all commercial vitamin C (ascorbic acid) preparations are manufactured synthetically, but at least one pilot plant has been established for the purpose of isolating vitamin C from citrus juices and from the liquors formed

Fig. 20. Chart of citrus fruits products. (From Joseph, 1947.) See text for comments.

from the waste products at the citrus canneries. These liquors have been found to contain from 2.5 to 1 5 0 mg of vitamin C per 1 0 0 ml of liquor. Press liquors.—Press liquors from citrus wastes are said to contain from 4 to 6 per cent total sugars. With the proper manipulation, yeasts could be grown on these liquors. Every hundred pounds of sugar could produce approximately 5 0 pounds of dried yeasts. Yeasts contain about 50 per cent protein and are considered to be the richest source for the B group of vitamins.

Products and Their Uses

• 139

Peel Essential oil.—The

amount of lemon oil produced in

the United States was estimated to be 800,000 pounds in 1943 and 400,000 pounds in 1944. The oil obtained by the cold press method, though less in quantity (four to six pounds per ton of lemons), is considered to be of a quality that is superior to that obtained by distillation. It is used for flavoring beverages, confections, certain bakery products, and in perfumes, pharmaceuticals, etc. Kesterson and McDuff (1948) have published recently on commercial methods of production and on chemical and physical properties of essential oil in the peel of Florida oranges, grapefruit, tangerines, and limes. One determination showed that the characteristics of the oil of the Meyer lemon more nearly resembled those of the oil of the true lemon than of any of the other four species tested. The Meyer lemon (lemonange?) is thought to be a hybrid between the lemon and some other species of Citrus. Pectin.—Pectin

is discussed under the heading " P e e l " because

that is where most of the pectin in the lemon fruit is found. Dr. Glenn H. Joseph of the California Fruit Growers Exchange Research Laboratory at Corona, California, has recently stated (verbally) that the food value of 1 gram of pectin equals approximately 3700 small calories. One ton of lemons yields from 10 to 20 pounds of pectin. These figures refer to pectin as extracted and not to commercial pectin which has been mixed with corn sugar to reduce its " g r a d e " to some constant value such as 100 or 150. Total production of pectin from citrus in the United States increased from about 1,500,000 pounds just before our entry into the war to 4,000,000 pounds in 1944. Approximately 95 per cent of the pectin is used in food products such as jellies, jams, preserves, marmalades, puddings, fruit salads, candy, and sherbet. Some of the other uses for various types of pectin are: an emulsifying agent in foods, cosmetics, and

140 •

The Lemon Fruit

pharmaceuticals; hemostatic injections, and as an emergency fluid for intravenous use in controlling shock; industrial uses such as steel, rubber, and paper making; in drilling for oil to prevent water seepage into the wells; and for making pastes, salves, tablets, powders, and suspensions. For a discussion of parenteral use of pectin sols, see Joseph (1950), who gives a review of medical literature on more than 600 clinical cases where pectin sols were used intravenously in studying treatment of shock. Candied peel.—The making of candied citrus peel has become an important industry. Either fresh or brined peel may be used. The spent syrup after the sugar-impregnated peel has been removed, may be sold in competition with such table syrups as maple, sorghum, and cane, and may be used as a base for bakers' jelly. "Vitamin P."—Hesperidin is the oldest commercially available "vitamin P " material (see "Hesperidin," p. 3 1 ) . "Hesperidin, methylated chalcone," obtained by the methylation of hesperidin, is a valuable member of the "vitamin P " group. Two other substances which have therapeutic values similar to those of the more refined "vitamin P " are made from lemon peel and are called "Lemon Peel Infusion, Dried" and "Calcium Flavonate Glycoside, Lemon." Enzymes.—An enzyme, pectin esterase (pectase), can be isolated from both the albedo and the flavedo of the peel. In powder form the enzyme can be used for the conversion of pectin to pectinic acid. In conjunction with a glycoside enzyme, it may be used also for juice clarification and as a filter aid. Galacturonic acid.—Nanji (1933) found that about 9 mg of galacturonic acid in the form of a white crystalline powder could be obtained from each 100 grams of lemon peel. Since Nanji obtained his results, many investigators have obtained much greater yields of galacturonic acid by hydrolyzing commercial pectin or pectin-bearing substrates with pectic enzymes such as "Pectinol." To cite two of the more recent ex-

Products and Their Uses

• 141

amples, Rietz and Maclay (1943) used 170-, 185- and 200-grade citrus pectin and obtained yields of 80, 78 and 74 per cent galacturonic acid, based on the uronic anhydride content of the pectin. After Isbell and Frush (1944) discovered the low solubility of certain salts of galacturonic acid, Frush and Isbell (1944) found that after hydrolyzing citrus pectin and pectic acid with Pectinol, good yields of calcium, sodium calcium and sodium strontium galacturonates could be obtained from the hydrolyzates. About 75 per cent of the galacturonic acid content of the pectin, and about 93 per cent of the galacturonic acid content of the pectic acid were obtained. Galacturonic acid is used principally for analytical and biochemical studies, and for pharmaceutical purposes.

Juice Citric acid.—Lemon juice contains about 5 to 7 per cent citric acid. The lemon is the only domestic fruit in the United States that contains enough citric acid to make its recovery commercially profitable. One ton of lemons yields from 30 to 40 pounds of citric acid (as hydrate, crystals). About 1,500,000 pounds of citric acid were produced from lemons in the United States in the fiscal year 1944—45. This amount, however, is very small in comparison with the amount that is made each year synthetically by mycological methods. Von Loesecke (1945) describes this method in detail and Cochrane (1948) states that about 17,000,000 pounds of citric acid are being produced annually in the United States by the mycological method. Citric acid is used in pharmaceutical preparations, soft drinks, food, candies, jelly making, and, in the form of sodium citrate, as an emulsifying agent for processed cheese. Some is used also in silvering, engraving, inks, and for dyeing and calico printing. It is of interest that over half of the citric acid produced in the United States is used in medicine and about a fourth of it is used

The Lemon Fruit

142 •

by food and beverage industries. The esters of citric acid are also of interest because of their use in the fields of plastics and synthetic resins (Cochrane, 1948). Beverages.—At the present time about one-third of the crop of California-Arizona lemons is sent to products plants for processing. In addition to citric acid, oil, pectin, etc., these lemons furnished the following amounts of juice for beverage purposes during 1947-1949 (California Fruit Growers Exchange, 1 9 5 0 ) :

Year

Fresh singlestrength juice Gallons

Frozen singlestrength juice Gallons

Concentrated 40° Brix juice Gallons

1947-48 1948-49

154,000 148,000

231,000 179,000

446,000 579,000

To the above group of beverage forms of lemon juice may now be added the frozen concentrate which first appeared on the market in 1950. That the frozen concentrate has found favor with the public is indicated by the fact that the estimated production for 1951 is 3,000,000 cases. To make lemonade, one 6-oz. can of the concentrate is diluted to one quart with water; the concentrate contains the sugar necessary for sweetening. Approximately 30,000 pounds of juice powder were also produced from processed lemons in 1 9 4 0 - 4 1 and about double this amount in 1948^19. Other uses.—Lemon juice in addition to its use as a source of citric acid, as a fresh beverage, and as a lemonade base, is valuable for use with many kinds of food, both fresh and packaged, because of the antioxidant effect of its vitamin-acid complex. It may be used also (with salt) as a bleach for stains; as a hair rinse; and has been used for tanning leather in Sicily.

Seeds Oil.—Oil is not commercially recovered from lemon seeds in California. Investigators in other countries have suggested that such a recovery might be profitable. Dried citrus seeds

Products and Their Uses

• 143

have been found to contain 30 to 50 per cent oil. Lemon seed oil is semi-drying and resembles cotton seed oil. Suggested uses are for soap making and as a substitute for raisin seed oil. Cook et al. ( 1 9 4 6 ) report that lemon seed oil can be made for about 8 cents a pound. Peroxidase.—As

a result of his studies, Davis (1942) thinks

that it may be possible to obtain peroxidase in commercial quantities from lemon seeds which are available at product plants and which at present are usually considered to be a waste product of little or no value. Stock feed.—Such

a use is possible, after the oil has been re-

moved, because de Villiers (1931) reports that the pressed seed cake contains 43 per cent carbohydrates, 17 per cent protein, 9 per cent fat, and 4 per cent mineral matter. Similarly, Cook et al. ( 1 9 4 6 ) report 21.6 per cent protein and 13.95 per cent crude fat.

LITERATURE CITED A J O N , GUIDO.

1926. Ossidasi citriche. Congresso Nazionale di Chimica Pura ed Applicata (Palermo) Atti, 11:1092-1119. AMERICAN PHARMACEUTICAL ASSOCIATION.

1946. The national formulary. 8th ed. 850 p. The Association, Washington, D.C. (See especially: 374—77.) ANDRE, M . G .

1920a. Sur l'inversion du sucre de canne pendant la conservation des oranges. (Paris) Acad, des Sci. Compt. Rend. 170:126-28. 19206. Sur l'inversion du saccharose dans le sue d'orange. [Paris] Acad, des Sci. Compt. Rend. 170:292-95. ARIZONA CITRUS.

1949. Arizona citrus: a cooperative survey by the . . . U. S. Dept. of Agriculture . . . the University of Arizona Agr. Expt. Sta., and the Desert Grapefruit Industry Committee, Inc. 22 p. AXELROD, BERNARD.

1947. Citrus fruit phosphatase. Jour. Biol. Chem. 167:57-72. B A C H A R A C H , ALFRED L O U I S , P H Y L L I S MARGARET C O O K , a n d E R N E S T LESTER S M I T H .

1934. The ascorbic acid content of certain citrus fruits and some manufactured citrous products. Biochem. Jour. 105:1038^17. BAIER, W . E . , a n d T . C . M A N C H E S T E R .

1949. Inositol and folic acid in citrus fruit. Calif. Citrog. 34:361-63. BAILEY, H . S . , a n d C . P . WILSON.

1916. The composition of sound and frozen lemons with special reference to the effect of slow thawing on frozen lemons. Jour. Indus, and Engin. Chem. 8:902-04. BALLS, A . K .

1947. Enzyme actions and food quality. Food Technol. 1:245-51. BALLS, A . K . , a n d W . S . H A L E .

1933. Determination of peroxidase in agricultural products. Jour. Assoc. Off. Agr. Chem. 16:445-53. BARTHOLOMEW, E . T .

1923. Internal decline of lemons. II. Growth rate, water content, and acidity of lemons at different stages of maturity. Amer. Jour. Bot. 10:117-26. 1926. Internal decline of lemons. III. Water deficit in lemon fruits caused by excessive leaf evaporation. Amer. Jour. Bot. 13:102-17. 1928. Internal decline (endoxerosis) of lemons. VI. Gum formation in the lemon fruit and its twig. Amer. Jour. Bot. 15:548-63. 1937. Endoxerosis, or internal decline, of lemon fruits. Calif. Agr. Expt. Sta. Bui. 605:1-42.

144 •

Literature Cited

• 145

BARTHOLOMEW, E . T . , a n d H . S . REED.

1943. General morphology, histology, and physiology. In: Webber, H. J., and L. D. Batchelor (eds.). The citrus industry 1:669-717. Univ. of Calif. Press, Berkeley and Los Angeles. (See esp. p. 697.) BARTHOLOMEW, E . T . , a n d WILLIAM J . ROBBINS.

1926. Internal decline (endoxerosis) of lemons. IV. The carbohydrates in the peel of healthy and endoxerotic fruits. Amer. Jour. Bot. 13:342-54. BARTHOLOMEW, E . T . , a n d W . B . SINCLAIR.

1943. Soluble constituents and buffer properties of orange juice. Plant Physiol. 18:185-206. 1945. Apparatus for the determination of volatile citrus oils. Jour. Assoc. Off. Agr. Chem. 28:339-45. 1946. Factors influencing the volatile oil content of the peel of immature and mature oranges. Plant Physiol. 21:319-31. BATCHELOR, LEON DEXTER, a n d HERBERT J O H N WEBBER, E d s .

1948. The Citrus Industry. Vol II. Production of the crop. 933 p. Univ. of Calif. Press, Berkeley and Los Angeles. BERNAYS, F R .

1841. Limonin. Liebigs Ann. Chem. 40:317-18. BERTRAND, GABRIEL, a n d B O J E BENZON.

1928. Sur la teneur en zinc des principaux aliments d'origine végétale. Soc. Sci. d'Hyg. Aliment. Bul. n.s. 16:457-63. BIALE, J . B .

1940. Effect of vapors from moldy fruits on.coloring and respiration of lemons. Calif. Citrog. 25:186-212. BIALE, J . B . , a n d A . D . SHEPHERD.

1941. Respiration of citrus fruits in relation to metabolism of fungi. 1. Effects of emanations of Pénicillium, digitatum, Sacc., on lemons. Amer. Jour. Bot. 28:263-70. BIALE, J . B . , a n d R . E . YOUNG.

1947. Critical oxygen concentrations for the respiration of lemons. Amer. Jour. Bot. 34:301-09. BINET, LÉON, a n d GEORGES WELLER.

1934. Le dosage du glutathion réduit dans les tissues. Soc. de Chim. Biol. Bul. 16:1284-96. BOURQUELOT, E . , a n d H . HÉRISSEY.

1898. Sur l'existence dans l'orge germée d'un ferment soluble agissant sur la pectine. [Paris] Acad. des Sci. Compt. Rend. 127:191-94. BRACONNOT, HENRI.

1825. Recherches sur un nouvel acide universellement répandu dans tous les végétaux. Ann. de chim. et de phys., Ser. 2,28:173-78. BRANDES, RUDOLPH.

1828. Chemische Untersuchung der unreifen Pomeranzenfruchte. Arch, des Apothekervereins 27:113-37. BRAVERMAN, J . B . S .

1949. Citrus products: chemical composition and chemical technology. 424 p. Interscience Publishers, Inc., New York. BRIDGHAM, CATHERINE M . , a n d C . G . KING.

1933. The composition of lemon albedo pectin. Jour. Amer. Chem. Soc. 55:3319-22. BRUCKNER, V . , a n d A . SZENT-GYORGYI.

1936. Chemical nature of citrin. Nature 138:1057. BRYANT, EDWIN F . , GRANT H . PALMER, a n d GLENN H . JOSEPH.

1944. Determination of pectin in biological materials. Modifications of pentose furfural method. Indus, and Engin. Chem., Analyt. Ed. 16:74-76.

146 •

Literature Cited

CALDWELL, J O S E P H S .

1934. Hydrion concentration changes in relation to growth and ripening in fruits. U. S. Dept. Agr. Tech. Bui. 403:1-54. CALIFORNIA F R U I T GROWERS EXCHANGE.

1945. First survey of world literature of "Vitamin P" and related substances. Nutr. Res. 5(1) :1—4; (2) :2-3; sup., April 1947 (mimeo.). 1946. Use of fresh citrus fruits in hospitals and other institutions; a handbook of basic information for dietitians and nurses. 32 p. Calif. Fruit Growers Exchange, Los Angeles 55. CALIFORNIA F R U I T GROWERS EXCHANGE. M A R K E T I N G RESEARCH D E P A R T M E N T .

1947. Statistical information on the citrus fruit industry. 44 p. 26 figs. 1950. Statistical information on the citrus fruit industry: Supplement. 12 p. C A M E R O N , S . H . , D . A P P L E M A N , a n d J . B . BIALOGLOWSKI.

1935. Seasonal changes in the nitrogen content of citrus fruits. Amer. Soc. Hort. Sci. Proc. 33:87-89. CARROLL, GEORGE H .

1943. The role of ascorbic acid in plant nutrition. Bot. Rev. 9:41-48. CHARABOT, E . , a n d A . H E B E R T .

1904. Formation des composes terpeniques dans les organes chlorophylliens. Bui. Soc. Chim. 31:402-09. CHACE, E . M .

1909. The occurrence of pinene in lemon oil. U. S. Dept. Agr. Bur. Chem. Cir. 46:1-24. CHACE, E . M . , C . P . WILSON, a n d C . G . CHURCH.

1921. The composition of California lemons. U. S. Dept. Agr. Bui. 993:1-18. CHATFIELD, CHARLOTTE, a n d LAURA I . M C L A U G H L I N .

1928. Proximate composition of fresh fruits. U. S. Dept. Agr. Circ. 50:1-19. CHEEMA, G . S.

1927. Notes on the lemon industry in Italy. Bombay Dept. Agr. Bui. 137:1-9. CLARK, WILLIAM G .

1947. The present status of "Vitamin P." Conf. on the Cultivation of Drug and Assoc. Econ. Plants in Calif. Proc. 1947:271-80. Calif. Dept. of Education. COCHRANE, VINCENT W .

1948. Commercial production of acids by fungi. Econ. Bot. 2:145-57. COLBY, G E O . E .

1893. California oranges and lemons. Calif. Agr. Expt. Sta. Rpt. 1891-92:99-113 1894. Analyses of California oranges and lemons. Calif. Agr. Expt. Sta. Rpt. 1892-93 and part of 1894:240-56. 1898. Analyses of oranges, lemons and pomelos. Calif. Agr. Expt. Sta. Rpt. 189597:161-62. COLBY, G . E . , a n d H . L . DYER.

1891a. Investigations of California oranges and lemons. Calif. Agr. Expt. Sta. Rpt. 1890:106-15. 18916. Investigations of California oranges and lemons. Calif. Agr. Expt. Sta. Bui. 93:1-6. C O O K , H U G H L . , et

al.

1946. Readjustments in processing and marketing citrus fruits. 190 p. U. S. Dept. Agr. Bur. Agr. Econ.. Washington, D.C. DAVIS, W . B .

1932. Deposits of oil in the juice sacs of citrus fruits. Amer. Jour. Bot. 19:101-05. 1942. The distribution and preparation of citrus peroxidase. Amer. Jour. Bot. 29:252-54. 1947. Determination of flavanones in citrus fruits. Indus, and Engin. Chem. Anal. Ed. 19:476-78.

Literature Cited

• 147

DENNY, F . E .

1924. Effect of ethylene upon respiration of lemons. Bot. Gaz. 77:322-29.

D E VILLIERS, FRANCIS J .

1931. Citrus by-products: orange and lemon seeds. Farming in So. Africa 6:132. DOUDOROFF, M .

1943. Studies on the phosphorolysis of sucrose. Jour. Biol. Chem. 151:351-61. DOUDOROFF, M . , N . K A P L A N , a n d W . Z . HASSID.

1943. Phosphorolysis and synthesis of sucrose with a bacterial preparation. Jour. Biol. Chem. 148:67-75.

DUFRENOY, J .

1929. A cytological study of water-soluble and fat-soluble constituents of citrus. Jour. Agr. Res. 38:411-29.

EMERSON, OLIVER H .

1948. The bitter principles of citrus fruit. I. Isolation of nomilin, a new bitter principle of the seeds of oranges and lemons. Jour. Amer. Chem. Soc. 7 0 : 545-19. 1949. The bitter principle in navel oranges. Food Technol. 3:248-50.

E S A U , KATHERINE.

1948. Anatomic effects of the viruses of Pierce's disease and phony peach. Hilgardia 18:423-82. FAWCETT, H . S .

1936. Citrus diseases and their control. 2d ed. 582 p. McGraw-Hill Book Co. New York and London. FAWCETT, H . S . , a n d L E O J . KLOTZ.

1948. Diseases and their control. In: Batchelor, L. D., and H. J . Webber (Eds.) The citrus industry, 11:495-596. Figs 168-193. Univ. of California Press, Berkeley and Los Angeles. (See esp. pp. 517-524) FORD, ERNEST S .

1942. Anatomy and histology of the Eureka lemon. Bot. Gaz. 104:288-305.

FRANCESCONI, L .

1929. Origine degli olii eteri nelle piante. Ann. di Chim. Appl. [Rome] 19: 333-43. FRANCESCONI, L . , M . MANFREDI, a n d B . ASTENGO.

1923. [Origin of essential oils in the plant and the relations between their components.] Cong. Naz. di Chim. Pur. Appl. Roma, Atti 1:396-97. (See Chem. Abs. 18:3404.1924.)

F R E M Y , EDMOND.

1840. Premiers essais sur la maturation des fruits: Recherches sur la pectine et l'acide pectique. Jour, de Pharm. et de Chim., Ser. 2, 26:368-93. F R U S H , HARRIETT L . , a n d HORACE S . ISBELL.

1944. Preparation of sodium strontium galacturonate from citrus products. Natl. Bur. Standards Jour. Res. 33:401-06. FUDGE, B . R .

1938. Magnesium deficiency in relation to the yield and chemical composition of seedy and commercially seedless varieties of grapefruit. Fla. State Hort. Soc. Proc. 51:34-43.

FURR, J . R . , a n d C . A . TAYLOR.

1939. Growth of lemon fruits in relation to moisture content of the soil. U. S. Dept. Agr. Tech. Bui. 640:1-71. GADDUM, L . W .

1934. The pectic constituents of citrus fruits. Fla. Expt. Sta. Bui. 268:1-23.

GALSTON, ARTHUR W . , a n d ROSAMOND S . B A K E R .

1949. Studies on the physiology of light action. II. The photodynamic action of riboflavin. Amer. Jour. Bot. 36:773-80.

148 •

Literature Cited

GAPONENKOV, T . K . , a n d S . S . ALESHIN.

1935. [Variations in the yield and composition of the essential oils of nutmeg sage in relation to climatological conditions, time of collection and state of the material to be distilled.] Jour. Appl. Chem., U.S.S.R. 8:1049-54. GAUBIDS, H . D .

1771. Adversaria varii argumenti. Leyden. [Quoted in: Jour, de Pharm. Ser. 2, 18:252 (1832) ; and, with title "first discovery of hesperidine" in: Amer. Jour. Pharm. 4:261 (1833).] GIROUD, A . , et

al.

1936. Relation entre l'acid ascorbic et les carotenoides. Bui. Soc. Chim. Biol. 18:573-89. GONZALEZ, L E O N G .

1948. Effects of freezing on the respiration rate of oranges and lemons. Amer. Soc. Hort. Sei. Proc. 51:132-36. GORE, H . C .

1911. Studies on fruit respiration. U. S. Dept. Agr. Bur. Chem. Bui. 142:1-40. GUENTHER, ERNEST.

1948. The essential oils. Vol. 1. 427 p. D. Van Nostrand Co., Inc., New York. 1950. The essential oils. Vol. 3. 777 p. D. Van Nostrand Co., Inc., New York. GUTHRIE, J . D .

1938. A new method for the determination of glutathione in tissues based on its reaction with sulphur to form hydrogen sulphide. Boyce Thompson Inst. Contrib. 9:223-32. HAAGEN-SMIT, A . J .

1948. The chemistry, origin and function of essential oils in plant life. In: Guenther, Ernest. The essential oils, 1:15-83. D. Van Nostrand Co., Inc., New York. HAAS, A . R . C.

1945a. Boron in citrus trees. Plant Physiol. 20:323-43. 19456. Boron content of citrus trees grown on various rootstocks. Soil Sei. 59 : 465-79. 1948. Effect of the rootstock on the composition of citrus trees and fruit. Plant Physiol. 23:309-30. HAAS, A . R . C., a n d L . J . KLOTZ.

1935. Physiological gradients in citrus fruits. Hilgardia 9:181-217. HAAS, A . R . C., a n d H . J . QUAYLE.

1935. Copper content of citrus leaves and fruit in relation to exanthema and fumigation injury. Hilgardia 9:143-77. HALL, J . A .

1925. Glucosides of the navel orange. Jour. Amer. Chem. Soc. 47:1191-95. H A L L E R , M . H . , P . L . HARDING, J . M . L U T Z , a n d D . H . R O S E .

1931. The respiration of some fruits in relation to temperature. Amer. Soc. Hort. Sei. Proc. 28:583-89. HALLER, M . H . , D E A N H . R O S E , J . M . L U T Z , a n d P A U L L . HARDING.

1945. Respiration of citrus fruits after harvest. Jour. Agr. Res. 71:327-59. HALMA, F . F .

1934. Some phases in the water relation of citrus. Amer. Soc. Hort. Sei. Proc. 31:108-09. HANSEN, ELMER.

1938. The effect of ethylene on pectic changes in ripening fruits. Amer. Soc. Hort. Sei. Proc. 36:427-28. HARDING, P A U L L . , a n d W . E . L E W I S .

1941. The relation of size of fruit to solids, acid and volume of juice in the principal varieties of Florida oranges. Fla. State Hort. Soc. Proc. 54:52-56.

Literature Cited

• 149

HARTMAN, B . G . , a n d F . HILLIC.

1934. Acid constituents of food products. Special reference to citric, malic, and tartaric acids. Jour. Assoc. Off. Agr. Chem. 17:522-31.

HARVEY, E . M .

1946. Changes in lemons during storage as affected by air circulation and ventilation. U. S. Dept. Agr. Tech. Bui. 908:1-32.

HARVEY, E . M . , a n d G . L . RYCG.

1936a. Physiological changes in the rind of California oranges during growth and storage. Jour. Agr. Res. 52:723^16. 19366. Behavior of citrus fruit under special respiratory conditions as an expedient index of vitality. Plant Physiol. 11:647-51.

HASSID, W . Z . , M . DOUDOROFF, a n d H . A . BARKER.

1944. Enzymatically synthesized crystalline sucrose. Jour. Amer. Chem. Soc. 66: 1416-19. 1947. Enzymatically synthesized disaccharides. Arch. Biochem. 14:29-37.

HASTINGS, A . B . , a n d D . D . VAN S L Y K E .

1922. The determination of the three dissociation constants of citric acid. Jour. Biol. Chem. 53:269-76.

HEID, J . L .

1941. The effect of ethylene treatment upon the recovery of citrus pectin. Food Products Jour. 21:100-03,125.

HENDRICKSON, H . M . , a n d J . R . M A C R I L L .

1948. Refrigeration of lemons and grapefruit. In: American Society of Refrigerating Engineers, Refrigerating Application Data, Section 18-R. 10 p.

HIGBY, R A L P H H .

1938. The bitter constituents of Navel and Valencia oranges. Jour. Amer. Chem. Soc. 60:3013-18. 1941. The chemical nature of hesperidin and its experimental medical use as a source of vitamin P—a review. Jour. Amer. Pharm. Assoc., Sci. ed. 30: 629-34. 1943. The chemical nature of vitamin P. Jour. Amer. Pharm. Assoc., Sci. ed. 32:74-77.

HODGSON, R . W . , a n d E . R . EGGERS.

1938. Rootstock influence on the composition of citrus fruits. Calif. Citrog. 23: 499,531.

HODGSON, R . W . , a n d A . H . WRIGHT.

1950. On the comparative resistance of citrus to low winter temperatures. Calif. Citrog. 35:502, 532, 536-39.

HOPKINS, F . G .

1906. The analyst and the medical man. Analyst 31:385-404. 1921. On an auto-oxidisable constituent of the cell. Biochem. Jour. 15:286-305.

HUSSEIN, A. Aziz.

1944. Respiration in the orange. Jour. Biol. Chem. 155:201-11.

HUSZAK, S .

1937. Ueber die Funktion des Peroxydase Systems der Pflanzen. Ztschr. Physiol. Chem. 247:239-49.

ISBELL, HORACE S .

1944. Synthesis of vitamin C from pectic substances. Natl. Bur. Standards Jour. Res. 33:45-61.

ISBELL, HORACE S . , a n d HARRIETT L . F R U S H .

1944. Preparation of salts of galacturonic acid from beet pulp. Natl. Bur. Standards Jour. Res. 33:389-400.

J A N S E N , EUGENE F . , ROSIE JANG, a n d L . R . MACDONNELL.

1947. Citrus acetylesterase. Arch. Biochem. 15:415-31.

150 •

Literature Cited

JANSEN, EUCENE F . , a n d L . R . MACDONNELL.

1945. Influence of methoxyl content of pectic substances on the action of polygalacturonase. Arch. Biochem. 8:97-112. JOSEPH, GLENN H .

1947. Citrus products—a quarter century of amazing progress. Econ. Bot. 1 : 415-26. 1950. Parenteral use of pectin sols. Fluid replacement therapy in emergency treatment of shock. 23 p. Calif. Fruit Growers Exchange Res. Dept., Ontario, Calif. J O S E P H , G L E N N H . , A . HARRIS K I E S E R , a n d E D W I N F . BRYANT.

1949.

High polymer, ammonia-demethylated pectinates and their gelation. Food Technol. 3:85-90.

JOSLYN, M . A . , a n d G . L . MARSH.

1937. Utilization of fruit in commercial production of fruit juices. Calif. Agr. Expt. Sta. Circ. 344:1-63. JOSLYN, M . A . , a n d H . J . P H A F F .

1947. Recent advances in the chemistry of pectic substances. Wallerstein Labs. Communs. 10(29) :39-56. J O S L Y N , M . A . , a n d A . SEDKY.

1940. The relative rates of destruction of pectin in macerates of various citrus fruits. Plant Physiol. 15:675-87. KARRER, P A U L , a n d E R N S T J U C K E R .

1950. Carotenoids. (Trans, and rev. by Ernest A. Braude.) 384 p. Elsevier Pub. Co., Inc., New York, Amsterdam, London, and Brussels. KELLEY, W . P . , a n d A . B . CUMMINS.

1920. Composition of normal and mottled citrus leaves. Jour. Agr. Res. 20: 161-91. KERTESZ, Z . I .

1936. Pectic enzymes. Ergeb. der Enzymforsch. 5:233-58. KERTESZ, Z . I . , GEORGE L . B A K E R , G L E N N H . J O S E P H , H . H . M O T T E R N , a n d A K S E L G . OLSEN.

1944. Report of the committee for the revision of the nomenclature of pectic substances. Chem. and Engin. News 22:105-06. KESTERSON, J . W . , a n d O . R . M C D U F F .

1948. Florida citrus oils. Fla. Agr. Expt. Sta. Bui. 4 5 2 : 1 ^ 4 . K I N C , GLADYS S .

1947. Peripheral deposits of citrus fruit vesicles stained by oil-soluble dyes. Amer. Jour. Bot. 34:427-31. LEBRETON, P .

1828. Note sur la matière cristalline des orangettes, et analyse de ces fruits non encore développés, famille des Hesperidées. Jour, de Pharm. et de Chim., ser. 2. 14:377-92. LEFEVRE, K . U . , a n d B . T O L L E N S .

1907. Untersuchuengen iiber die Glucuronsaure, ihre quantitative Bestimmung und ihre Farbenreaktionen. Ber. Deut. Chem. Gesell. 40:4513-23. LINDOW, C . W . , C . A . E L V E H J E M , a n d W . H . PETERSON.

1929. The copper content of plant and animal foods. Jour. Biol. Chem. 82:465-71. LINEWEAVER, H A N S , a n d GERALD A . B A L L O U .

1945. The effect of cations on the activity of alfalfa pectinesterase (pectase). Arch. Biochem. 6:373-87. LORENZ, A . J . , a n d L . J . ARNOLD.

1941. Preparation and estimation of crude citrin solutions (Vitamin P) from lemons. Food Res. 6:151-56.

Literature Cited

• 151

LUBIMENKO, V., a n d M . NOVIKOFF.

1914. [Formation of essential oil in Ocymum basilicum in different intensities of light.] Bui. Appl. Bot. 7:697-724. M A C D O N N E L L , L . R . , E U G E N E F . J A N S E N , a n d H A N S LINEWEAVER.

1945. The properties of orange pectinesterase. Arch. Biochem. 6:389^01. M A C R I L L , J . R . , R . D . NEDVIDEK, a n d H . W . N I X O N .

1946. Citrus fruits. In: American Society of Refrigerating Engineers, Refrigerating Applications. 2d ed., Section 14, p. 145-60. MCCREADY, R . M . , E . D . WALTER, a n d W . D . MACLAY.

1950. Sugars of citrus juices. Food Technol. 4:19-20. MCHARGUE, J . S.

1924. The association of manganese with vitamins. Jour. Agr. Res. 27:417-24. MCNAIR, JAMES B .

1926. Citrus products. Field Mus. Nat. Hist., Pub. No. 238, Botanical Ser. 6:1-392. M E A D , S . W . , a n d H . R . GUILBERT.

1927. The digestibility of certain fruit by-products as determined for ruminants. Part II. Dried pineapple pulp, dried lemon pulp, and dried olive pulp. Calif. Agr. Expt. Sta. Bui. 439:1-11. M E Y E R , BERNARD S . , a n d DONALD B . ANDERSON.

1939. Plant Physiology. 696 p. D. Van Nostrand, New York. M E Y E R S , P H I L I P B . , a n d GEORGE L . B A K E R .

1929. Fruit Jellies VI. The role of pectin. 2. The extraction of pectin from pectic materials. Del. Agr. Expt. Sta. Bui. 160:1-64. 1931. Fruit Jellies VII. The role of pectin. 3. Effect of temperature upon the extraction of pectin. Del. Agr. Expt. Sta. Bui. 168:1^16. MILLER, EDWIN C .

1938. Plant Physiology. 2d ed. 1201 p. McGraw-Hill Book Co., Inc., New York and London. MILLER, E . V .

1946. Physiology of citrus fruits in storage. Bot. Rev. 12:393-423. MILLER, E . V . , a n d H . A . SCHOMER.

1939. Physiological studies of lemons in storage. Jour. Agr. Res. 59 : 601-07. MILLER, ERSTON V . , a n d J . R . WINSTON.

1939. Investigation of the development of color in citrus fruits. Fla. State Hort. Soc. Proc. 52:87-90. M I L L E R , ERSTON V . , J . R . W I N S T O N , a n d D . F . F I S H E R .

1940. Production of epinasty by emanations from normal and decaying citrus fruits and from Penicillium digitatum. Jour. Agr. Res. 60:269-77. MOLISCH, HANS.

1913. Mikrochemie der Pflanze. 394 p. Gustav Fischer, Jena. (See esp. p. 165, fig. 55.) M O N E Y , R . W . , a n d ( M R S . ) W . A . CHRISTIAN.

1950. Analytical data of some common fruits. Jour. Sci. Food and Agric. 1:8-12. M Y E R S , VICTOR C . , a n d HILDA M . CROLL.

1921. The determination of carbohydrates in vegetable foods. Jour. Biol. Chem. 46:537-51. NANJI, HOMI RUTTONJI.

1933. The preparation of galacturonic acid from plant materials, with a note on some of its derivatives. Biochem. Jour. 27:1163-65. NELSON, E . K .

1928. The acids of fruits. Amer. Med. 34:812-15. N O L T E , A R T H U R J . , GEORGE N . P U L L E Y , a n d HARRY W . VON L O E S E C K E .

1942. Experiments with antioxidants for preventing flavor deterioration in canned orange juice. Food Research 7:236-43.

152 •

Literature Cited

NOLTE, ARTHUR J . , a n d HARRY W . VON LOESECKE.

1940. Chemical and physical characteristics of the petroleum ether soluble material of fresh and canned Florida Valencia orange juice. Food Res. 5: 457-67. NORMAN, ARTHUR GEOFFREY.

1928. Studies on pectin. Part III. The degree of esterification of pectin in the juice of the lemon. Biochem. Jour. 22:749-52. NORRIS, FREDERICK WALTER.

1926. The pectic substances of plants. Part IV. The pectic substances in the juice of oranges. Biochem. Jour. 20:993-97. NORRIS, FREDERICK WALTER, a n d CARL E M I L R E S C H .

1935. The analysis of carbohydrates of the cell wall of plants. I. The relation between uronic anhydride content and furfuraldehyde yield. Biochem. Jour. 29:1590-96. ONSLOW, M . W .

1920. Oxidizing enzymes. III. The oxidizing enzymes of some common fruits. Biochem. Jour. 14:541^17. PENZIC, OTTO.

1887. Studi botanici sugli agrumi e sulle piante affini. Tip. Erdi Botta, Rome. (Italy. Ministero di Agricoltura e Comercio. Annali di Agricoltura, No. 116.) 6 + 590 p. and atlas of 58 pis. PETERSON, W . H . , a n d C . A . E L V E H J E M .

1928. The iron content of plant and animal foods. Jour. Biol. Chem. 78:215-23. PETERSON, W . H . , a n d J . T . SKINNER.

1931. Distribution of manganese in food. Jour. Nutr. 4:419-26. P H A F F , H . J . , a n d M . A . JOSLYN.

1947. The newer knowledge of pectic enzymes. Wallerstein Labs. Communs. 10 (30):133-48. P H I L L I P S , M A X , M . J . Goss, and C. A. BROWNE. 1933. Determination of uronic acids and methoxyl in certain plants and plant materials. Jour. Assoc. Off. Agr. Chem. 16:289-92. PIERCE, E . C . , a n d C . O . APPLEMAN.

1943. Role of ether soluble organic acids in the cation-anion balance in plants. Plant Physiol. 18:224r-38. POORE, H . D .

1932. Analyses and composition of California lemon and orange oils. U. S. Dept. Agr. Tech. Bui. 241 :l-30. POWERS, JUSTIN, et

al.

1940. A symposium on pectin and pectin pastes. Natl. Formulary Committee Bui. 9:1-39. PRIESTLEY, J . H .

1943. The cuticle in angiosperms. Bot. Rev. 9:593-616. PRITCHETT, D . E . , a n d HAROLD E . MERCHANT.

1946. The purification of hesperidin with formamide. Jour. Amer. Chem. Soc. 68:2108-09. QUARTAROLI, A .

"1928. Sulla questione del rame come componente normale delle piante. Ann. Chim. Appl. (Rome) 18:47-63. RABAK, FRANK.

1916. The effect of cultural and climatic conditions on the yield and quality of peppermint oil. U. S. Dept. Agr. Bui. 454:1-16. REED, G . B .

1914. The oxidases of acid tissues. Bot. Gaz. 57:528-30.

Literature Cited

• 153

REED, H . S.

1919. Certain relationships between the flowers and the fruits of the lemon. Jour. Agr. Res. 17:152-65. 1930. The swelling of citrus fruits. Amer. Jour. Bot. 17:971-82. REED, H . S . , a n d E . T . B A R T H O L O M E W .

1927. Water translocation in young fruits. Science 66:382. RICEVUTO, A .

1933. La formazione dell'acido citrico nel limone.—Nota preliminare. Ann. Chim. Appl. (Rome) 23:411-13. RIETZ, E . , a n d W . D . MACLAY.

1943. Preparation of ¿-galacturonic acid from pectin. Jour. Amer. Chem. Soc. 65:1242-43. ROHRBAUCH, P . W . , a n d J . R . MACRILL.

1943. Ethylene in lemon storage rooms. Calif. Citrog. 28:118. ROSENBERG, H . R .

1942. Chemistry and physiology of the vitamins. 674 p. Interscience Publishers, Inc., New York. R o y , WALLACE R .

1945. Effect of potassium deficiency and of potassium derived from different sources on the composition of the juice of Valencia oranges. Jour. Agr. Res. 70:143-69. R U B I N , B . A . , E . V . ARTSIKHOVSKAYA, a n d T . M . IVANOVA.

1948. [Respiratory gas exchange in the citrus plants and its role in the stability of the fruit.] Akad. Nauk S.S.S.R. Doklady 60:425-27. (See Chem Abs. 43:8453.) R U S Z N Y A K , S T . , a n d A . SZENT-GYORGYI.

1936. Vitamin P : Flavonols as vitamins. Nature 138:27. SAUNDERS, F E L I X .

1931. Studies in proteins. II. Concerning the uniformity of the protein fraction extracted from orange seed meal by salt solutions. Jour. Amer. Chem. Soc. 53:696-700. SCARBOROUGH, H .

1945. Observations on the nature of vitamin P and the vitamin P potency of certain foodstuffs. Biochem. Jour. 39:271-78. SCHOPFER, W . H .

1943. Plants and vitamins. 293 p. The Chronica Botanica Co., Waltham, Mass. SCOTT, FLORA MURRAY.

1948. Internal suberization of plant tissues. Science 108:654^-55. SCOTT, F L O R A MURRAY, a n d K A T H E R I N E C . B A K E R .

1947. Anatomy of Washington Navel orange rind in relation to water spot. Bot. Gaz. 108:459-75. SHERMAN, HENRY C .

1946. Chemistry of food and nutrition. 7th ed. 675 p. The Macmillan Co. SINCLAIR, W A L T O N B . , a n d E . T . B A R T H O L O M E W .

1935. Methods for determining pentoses as furfural in citrus fruits. Amer. Jour. Bot. 22:829-42. 1944. Effects of rootstocks and environment on the composition of oranges and grapefruit. Hilgardia 16:125-78. SINCLAIR, W . B . , E . T . B A R T H O L O M E W , a n d R . D . NEDVIDEK.

1935. The isolation and distribution of nitrogen in dilute alkali-soluble proteins of healthy Valencia and Washington Navel orange fruits. Jour. Agr. Res. 50:173-80. SINCLAIR, W . B . , E . T . B A R T H O L O M E W , a n d R . C . R A M S E Y .

1945. Analysis of the organic acids of orange juice. Plant Physiol. 20:3-18.

154 •

Literature Cited

SINCLAIR, W A L T O N B . , a n d P A U L R . CRANDALL.

1949. Carbohydrate fractions of lemon peel. Plant Physiol. 24:681-705. SINCLAIR, W . B . , a n d D . M . E N Y .

1945. The organic acids of lemon fruits. Bot. Gaz. 107:231^12. 1946a. Significance of the alkaline ash of citrus juices. Proc. Amer. Soc. Hort. Sci. 47:119-122. 19466. Stability of the buffer system of lemon juice. Plant Physiol. 21:522-32. 1947a. Ether-soluble organic acids and buffer properties of citrus peels. Bot. Gaz. 108:398^07. 19476. Ether-soluble organic acids of mature Valencia orange leaves. Plant Physiol. 22:257-69. SINCLAIR, W . B . , a n d R . C . R A M S E Y .

1944. Changes in the organic-acid content of Valencia oranges during development. Bot. Gaz. 106:140-48. SMITH, A . H .

1925. A protein in the edible portion of orange. Preliminary paper. Jour. Biol. Chem. 63:71-73. SOMOCYI. J . C .

1944.

[Active principles which inhibit the destruction of vitamin C in vitro.] Helvetica Physiol, et Pharmacol. Acta. 2:269-74.

SPOEHR, H . A .

1919. The carbohydrate economy of cacti. Carnegie Inst. Washington Publ. 287: 1-79. STAHL, A . L .

1935.

Composition of miscellaneous tropical and subtropical Florida fruits. Fla. Agr. Expt. Sta. Bui. 283:1-20.

STEVENS, J . W . , a n d W . E . BAIER.

1939. Refractometric determination of soluble solids in citrus juices. Indus, and Engin. Chem., Analyt. Ed. 11:447-49. STEWART, W . S .

1948. The effects of 2,4-D and 2,4,5-T on citrus fruit storage. Citrus Leaves 28 (11) :5-7,24-27. STEWART, W M . S . , a n d H . Z . H I E L D .

1950. Effects of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid on fruit drop, fruit production, and leaf drop of lemon trees. Proc. Amer. Soc. Hort. Sci. 55:163-171. STEWART, W M . S . , J . W . P A L M E R , a n d H . Z . H I E L D .

1950. Packinghouse experiments on the use of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid to increase the storage life of lemons. (In press.) SUCHARIPA, R U D O L P H .

1924. Protopectin and some other constituents of lemon peel. Jour. Amer. Chem. Soc. 46:145-56. SWIFT, L . J .

1946. Determination of crude lipid in citrus juice. Jour. Assoc. Off. Agr. Chem. 29:389-95. THOMAS, E . E . , H . D . YOUNG, a n d C . O . SMITH.

1919. A study of the effects of freezes on citrus in California. II. Changes that take place in frozen oranges and lemons. Calif. Agr. Expt. Sta. Bui. 304: 299-314. TRESSLER, DONALD K . , MAYNARD A . J O S L Y N , a n d GEORGE L . M A R S H .

1939. Fruit and vegetable juices. 549 p. The Avi. Pub. Co., Inc., New York. T U P P E R - C A R E Y , R . M . , a n d J . H . PRIESTLEY.

1923. The composition of the cell wall at the apical meristem of stem and root. Roy. Soc. (London) Proc. Ser. B, 95:109-31.

• 155

Literature Cited TURRELL, FRANKLIN M .

»

1946. Tables of surfaces and volumes of spheres and of prolate and oblate spheroids, and spheroidal coefficients. 153 p. Univ. of Calif. Press. Berkeley and Los Angeles.

TURRELL, F . M .

1950. A study of the physiological effects of elemental sulphur dust on citrus fruits. Plant Physiol. 2 5 : 1 3 - 6 2 . TURRELL, F . M . , a n d L . J . K L O T Z .

1940. Density of stomata and oil glands and incidence of water spot in the rind of Washington Navel orange. Bot. Gaz. 1 0 1 : 8 6 2 - 7 1 . TURRELL, F . M . , a n d D . L . S L A C K .

1948. Specific gravity of citrus fruits. Amer. Soc. Hort. Sci. Proc. 5 2 : 2 4 5 - 5 0 . VAN DER P L A N K , J . E . , et

al.

1939. The storage of lemons. Union So. Africa Dept. Agr. and For. Low Temp. Res. Lab., (Capetown) Rpt. 1 9 3 7 - 3 8 : 1 5 6 - 6 9 .

VAN S L Y K E , D . D .

1922. On the measurement of buffer values and on the relationship of buffer value to the dissociation constant of the buffer and the concentration and reaction of the buffer solution. Jour. Biol. Chem. 5 2 : 5 2 5 - 7 0 . VAUQUELIN, L O U I S NICOLAS.

1790. Analyse du Tamarin, et réflexions sur quelques-unes de ses préparations médicinales. Ann. de Chim. 5 : 9 2 - 1 0 6 . V I C K E R Y , H . B . , E . M . NELSON, H . J . A L M Q U I S T , a n d C . A . E L V E H J E M .

1950. Term "Vitamin P " recommended to be discontinued. Science 1 1 2 : 6 2 8 . V O N L O E S E C K E , HARRY W .

1945. A review of information on mycological citric acid production. Chem. and Engin. News 2 3 : 1 9 5 2 - 5 9 . WAYNICK, D . D .

1927. Growth rates of Valencia oranges. Calif. Citrog. 1 2 : 1 5 0 , 1 6 4 . W E A T H E R B Y , L . S . , a n d A M B E R L . S . CHANC.

1943. The determination of flavones or quercetin-like substances in certain naturally occurring products. Jour. Biol. Chem. 1 4 8 : 7 0 7 - 0 9 . W E B B E R , HERBERT J O H N , a n d LEON D E X T E R BATCHELOR, E d i t o r s .

1943. The Citrus Industry. Vol. I. History, botany, and breeding. 1028 p. Univ. of Calif. Press, Berkeley and Los Angeles. WIDDOWSON, E . M . , a n d R . A . MCCANCE.

1935. The available carbohydrates of fruits. Determination of glucose, fructose, sucrose and starch. Biochem. Jour. 2 9 : 1 5 1 - 5 6 . WILLIMOTT, S . G., a n d F . WOKES.

1926. Oxidising enzymes in the peel of citrus fruits. Biochem. Jour. 2 0 : 1 0 0 8 - 1 2 . W I L S O N , C . P . , a n d C . O . YOUNC.

1917. A method for the determination of the volatile oil content of citrus fruits. Jour. Indus, and Engin. Chem. 9 : 9 5 9 - 6 1 . WILSON, C . W .

1939. A study of the boric acid color reaction of flavone derivatives. Jour. Amer. Chem. Soc. 6 1 : 2 3 0 3 - 0 6 . WILSON, C . W . , L . S . WEATHERBY, a n d W . Z . BOCK.

1942. Determination of certain quercetin-like substances. Indus, and Engin. Chem., Analyt. Ed. 1 4 : 4 2 5 - 2 6 . YOUNC, H . D .

1915. The composition of frozen oranges and lemons. Jour. Indus, and Engin. Chem. 7 : 1 0 3 8 ^ 1 . YOUNGBURG, G U Y E .

1927. Studies on pentose metabolism. II. A micro method for the determination of pentoses and pentosans. Jour. Biol. Chem. 7 3 : 5 9 9 - 6 0 6 .

AUTHOR INDEX

Ajon, Guido, 88,119 Aleshin, S. S., 24 Almquist, H. J., 127 American Pharmaceutical Association, 94,99 Anderson, Donald B., 21 Andre, M. G., 71 Appleman, C. 0., 80 Appleman, D., 114 Arizona Citrus, 3 Arnold, L. J., 127 Artsikhovskaya, E. V., 49, 56 Astengo, B., 23 Axelrod, Bernard, 121 Bacharach, Alfred Louis, 125 Baier, W. E., 14, 61, 62,124 Bailey, H. S., 15,16, 80, 81 Baker, George L., 94, 95 Baker, J. L., 51 Baker, Katherine C., 21 Baker, Rosamond S., 128 Ballou, Gerald A., 121 Balls, A. K., 49,119 Barber, Harlan E., 44,126 Barker, H. A., 71 Bartholomew, E. T., 7, 9, 26, 27-30, 36, 38^11, 43, 64, 67, 68, 70, 73, 80, 83, 84, 91,92,107-09,115,116,134 Batchelor, Leon Dexter, 1, 2, 29 Benzon, Boje, 132 Bernays, Fr., 35 Bertrand, Gabriel, 132 Biale, J. B„ 52,54 Bialoglowski, J. B., 114 Binet, Leon, 118

157 •

Bock, W. Z., 18 Bourquelot, E., 121 Braconnot, Henri, 94 Brandes, Rudolph, 31 Braverman, J. B. S., 18, 23, 25, 84, 124, 125,136 Bridgham, Catherine M., 95 Browne, C. A., 102 Bruckner, V., 34 Bryant, Edwin F., 99,103 Caldwell, Joseph S., 39 California Fruit Growers Exchange, 45, 73, 116, 123, 127, 129, 130, 142 California Fruit Growers Exchange, Marketing Research Department, 2 Cameron, S. H., 114 Carroll, George H., 128 Chace, E. M., 8, 15, 24, 27, 28, 67, 80, 89 Chang, Amber L. S., 18 Charabot, E., 24 Chatfield, Charlotte, 8, 36, 68, 80, 115, 129,135 Cheema, G. S., 12 Christian, (Mrs.) W. A., 60, 67, 80, 103 Church, C. G., 8,15, 24,27,67,80,89 Clark, William G., 127 Cochrane, Vincent W., 141, 142 Colby, George E., 8, 36, 67, 80, 113, 114, 128,135 Cook, Hugh L., 116,135 Cook, Phyllis Margaret, 125,136,143 Crandall, Paul R., 62-66, 90, 91, 96-103, 109,110,112,115,129,130,132 Croll, Hilda M„ 68 Cummins, A. B., 72

158 • Davis, W. B., 20, 21, 23, 29, 30, 33, 119, 120,143 Denny, F. E., 54 De Villiers, Francis J., 116,135,143 Doudoroff, M., 71 Dufrenoy, J., 18 Dyer, H. L., 8,36,113,135 Eggers, E. R., 60, 85 Elvehjem, C. A., 127,132 Emerson, Oliver H., 35 Eny, D. M„ 16, 17, 42, 43, 72-79, 82, 83, 85-89,130,133 Erickson, L. C., 11 Esau, Katherine, 109 Fawcett, H. S., 6,59 Fisher, D. F., 54 Ford, Ernest S., 7 Francesconi, L., 23, 28 Frémy, Edmond, 94,121 Frush, Harriett L., 141 Fudge, B. R., 135 Furr, J. R., 9,10,40 Gaddum, L. W., 105,108 Galston, Arthur W., 128 Gaponenkov, T. K., 24 Gaubius, H. D., 31 Giroud, A., 125 Gonzalez, Leon G., 47 Gore, H. C., 47 Goss, M. J., 102 Guenther, Ernest, 23, 24 Guilbert, H. R., 114,137 Guthrie, J. D., 118 Haagen-Smit, A. J., 23 Haas, A. R. C„ 8, 41, 43, 68, 72, 73, 12832 Hale, W. S„ 119 Hall, J. A., 34 Haller, M. H„ 47,49,55 Halma, F. F., 40 Hansen, Elmer, 102,103 Harding, Paul L., 9, 47, 49, 55 Hartman, B. G., 80, 81 Harvey, E. M., 33, 34, 44, 49-51, 56, 73, 126 Hassid, W. Z., 71 Hastings, A. B., 88 Hébert, A., 24 Heid, J. L., 103

Author Index Hendrickson, H. M., 46-48, 53 Hérissey, H., 121 Hield, H. Z„ 10,11,52,53 Higby, Ralph H., 31, 34,35,127 Hillig, F., 80, 81 Hodgson, R. W., 3,60,85 Hopkins, F. G., 117,123 Hussein, A. Aziz, 49,122 Huszak, S., 122 Isbell, Horace S., 125,141 Ivanova, T. M., 49, 56 Jang, Rosie, 122 Jansen, Eugene F., 120-22 Joseph, Glenn H., 94, 99, 103, 136, 13840 Joslyn, Maynard A., 9, 94, 120, 121, 123 Jucker, Ernst, 19 Kalmer, A. F., 25 Kaplan, N., 71 Karrer, Paul, 19 Kelley, W. P., 72 Kertesz, Z. I., 94,120,121 Kesterson, J. W„ 139 Kieser, A. Harris, 103 King, C. G., 22, 95 King, Gladys S., 30, 59 Klotz, Leo J., 6, 28,41,43,68,72,73,12830 Lebreton, P., 31 Lefevre, K. U., 93 Lewis, W. E., 9 Lindow, C. W., 132 Lineweaver, Hans, 121 Lorenz, A. J., 127 Lubimenko, V., 24 Lutz, J. M., 47,49,55 MacDonnell, L. R., 120-22 Maclay, W. D., 33,68,141 MacRill, J. R., 6,46-18,53, 54, 56 Manchester, T. C., 124 Manfredi, M., 23 Marsh, George L., 9,123 McCance, R. A., 68 McCready, R. M., 33,68 McDuff, O. R., 139 McHargue, J. S., 132 McLaughlin, Laura I., 8, 36, 68, 80, 115, 129,135

• 159

Author Index McNair, James B., 28 Mead, S. W., 114,137 Merchant, Harold E., 34 Meyer, Bernard S., 21 Meyers, Philip B., 95 Miller, Edwin C., 19 Miller, Erston V., 18, 33, 54, 56, 57, 64, 66,68, 70, 74, 120 Molisch, Hans, 32 Money, R. W., 59,67,80,103 Mottern, H. H., 94 Myers, Victor C., 68 Nanji, Homi Ruttonji, 140 Nedvidek, R. D„ 6,51, 53,116 Nelson, E. K., 81 Nelson, E. M , 127 Nixon, H. W., 6,53 Nolte, Arthur J., 21 Norman, Arthur Geoffrey, 107 Norris, Frederick Walter, 92, 99,107 Novikofl, M., 24 Olsen, Axel G., 94 Onslow, M. W., 119 Palmer, Grant H., 52, 53, 99 Penzig, Otto, 29 Peterson, W. H., 132 Phaff, H. J., 94, 121 Phillips, Max, 102 Pierce, E. C., 80 Poore, H. D., 28,29 Powers, Justin, 94 Priestley, J. H., 21,108 Pritchett, D. E., 34 Pulley, George N., 21 Quartaroli, A., 132 Quayle, H. J., 128,129,131,132 Rabak, Frank, 24 Ramsey, R. C., 84 Reed, G. B., 119 Reed, H. S„ 7,9,29,30,80,107,108 Resch, Carl Emil, 92, 99 Ricevuto, A., 88 Rietz, E., 141 Robbins, William J., 64, 67, 91, 92,109 Rohrbaugh, P. W., 54, 56 Rose, Dean H., 47, 49, 55 Rosenberg, H. R., 125,128 Roy, Wallace R., 70 Rubin, B. A., 49, 56

Rusznyak, St., 34 Rygg, G. L., 33,34,49, 51,73 Saunders, Felix, 117 Scarborough, H., 127 Schomer, H. A., 33, 56, 57, 64, 66, 68, 70, 74,120 Schopfer, W. H., 128 Scott, Flora Murray, 21, 22 Sedky, A., 120 Shepherd, A. D., 54 Sherman, Henry C., 132 Sinclair, Walton B„ 9, 16, 17, 26-28, 42, 43, 62-68, 70, 72-79, 82-92, 96-103, 109, 110, 112, 115, 116, 129, 130, 132, 133 Skinner, J. T., 132 Slack, D. L„ 16 Smith, A. H., 116 Smith, C. O., 15 Smith, Ernest Lester, 125 Somogyi, J. C., 122 Spoehr, H. A., 41 Stahl, A. L„ 8, 73 Stern, F., 124 Stevens, J. W., 14, 61, 62 Stewart, William S., 10,11, 50-53 Sucharipa, Rudolph, 109 Swift, L. J., 19, 21,22 Szent-Györgyi, A., 34 Taylor, C. A., 9, 10, 40 Thomas, E. E., 15 Tollens, B„ 93 Tressler, Donald K., 123 Tupper-Carey, R. M., 108 Turrell, Franklin M., 36 Turrell, F. M„ 16, 28, 72,117,118 Van der Plank, J. E„ 56 Van Slyke, D. D., 87, 88 Vauquelin, Louis Nicolas, 94 Vickery, H. B., 127 Von Loesecke, Harry W., 21,141 Walter, E. D., 33, 68 Waynick, D. D., 41 Weatherby, L. S., 18 Webber, Herbert John, 1, 2, 29 Weiler, Georges, 118 Widdowson, E. M., 68 Willimott, S. G., 119 Wilson, C. P., 8,15,16, 24, 27, 28, 67, 80, 81,89

160 • Wilson, C. W„ 18, 34 Winston, J. R., 18, 54 Wokes, F., 119 Wright, A. H., 3

Author Index Young, C. 0., 24, 28 Young, H. D., 13,15, 67-69, 80, 81 Young, R. E., 52, 54 Youngburg, Guy E„ 94

SUBJECT INDEX

Albedo browning—see Diseases and disorders Alternaria rot—see Diseases and disorders Ash, 128,132 Beverages—see Products and uses Black button—see Diseases and disorders Bitter principles, 34 limonin, 34 nomilin, 35 substance "X", 35 Buffer properties—see Organic acids

mottle-leaf, 19 peteca, 57 pitting, 57 red blotch, 57 water breakdown, 57 Distribution—see Lemon fruit

Calcium in peel, 79 (see also Inorganic constituents) Candied peel—see Products and uses Carbohydrates, 18 in green fruit, 18 Carotenoids, 17 Cellulose and hemicellulose, 109 Chemical changes—see Lemon fruit Chlorophylls, 17 Color grades—see Lemon fruit Color in peel, 17 Composition—see various headings

Endoxerosis—see Diseases and disorders Enzymes, 119 (see also Products and uses) and destruction of ascorbic acid, 122 and reduction of sucrose, 71 Essential oil, 23 (see also Products and uses) climatological effect on, 24 composition, 23, 28 environmental effect on, 27 extraction, 25 function, 30 in juice vesicles, 29 in peel, 24 specific gravity, 28 Ethylene and pectin quality, 102 and storage, 54 for coloring fruit, 18

Diseases and disorders albedo browning, 57 alternaria rot, 51, 56: control with 2,4D, 2,4,5-T, 51 black button, 51: control with 2,4-D, 2,4,5-T, 51 endoxerosis, 134 green mold, 55 membranous stain, 57

Flavanones, 33 orange and lemon content compared, 33 Flavonoids, 17,18 Freeze injury, susceptibility to, 3 Frozen lemons organic acids in juice, 81 specific gravity of juice, 14 sugar in, 69

161 •

162 • Galacturonic acid—see Polysaccharides; Products and uses Glutathione, 117 Glycosides, 33 under storage, 33 Grapefruit, 1 (and in passing) Growth-promoting substances, 10, 51 Harvest—see Lemon fruit Hesperidin, 31 accumulation during storage, 34 function, 34 isolation, 34 Inorganic constituents, 128 common elements, 129 total ash, 128 trace elements, 132 Juice, 141 (see also various headings) Lemon fruit age and size, 9 chemical changes in, 11 color grades, 4 composition—see various headings distribution, 2 fruit set, 3 harvest, 3 history, 1 maturity defined, 4 origin, 1 physiology—see various headings production, 2 products and uses—see Products and uses storage—see Storage structure, 6 varieties, 3 Lemon-seed oil, 22 (see also Products and uses) Limonin—see Bitter principles Lipids, 19 in juice, 21 in peel, 21 in seeds, 22 Maturity defined—see Lemon fruit Membranous stain—see Diseases and disorders Moisture, 35 and pH, 37 in juice, 43

Subject Index in peel, 41 in whole fruit, 35 Mottle-leaf—see Diseases and disorders Nomilin—see Bitter principles Oil—see Essential oil Orange (see also in passing) acid concentration in, 84 chemical changes in, 11 flavanones in, 33 rancidity in canned juice, 21 respiration, 49 soluble solids concentration in juice, 58 Organic acids, 74 in juice, 80: buffer properties, 85; concentration, 89; in frozen juice, 81; rootstock effect on, 85; in stem vs. stylar halves of fruit, 83 in peel, 74: buffer curves, 75; pH, 75 Origin—see Lemon fruit Pectate pulp—see Products and uses Pectic acid—see Products and uses Pectin, 94 (see also Products and uses) in juice, 105 in peel, 95: quality affected by ethylene, 102 in pulp, 103 physiological functions, 107 Peel (see also various headings) color in, 17 per cent weight of fruit, 8 thickness, 8 Pentosans, 92 Peroxidase—see Products and uses Peteca—see Diseases and disorders pH, 72 and moisture, 37 and organic acids, 75, 85 and sugars, 70 Physiology—see various headings Pitting—see Diseases and disorders Polysaccharides, 89 (see also Cellulose andhemicellulose; Pectin; Pentosans) Press liquors—see Products and uses Products and uses, 136 juice, 141: beverages, 142; citric acid, 141 peel, 139: candied, 140; enzymes, 140; essential oil, 139; galacturonic acid, 140; pectin, 139; vitamin " P " , 140

Subject Index seeds, 142: oil, 142; peroxidase, 143; stock feed, 143 whole fruit, 137: pectate pulp, 137; pectic acid, 137; press liquors, 138; stock feed, 137; vitamin C, 138 Proteins, 113 in edible portion, 115 in juice, 116 in peel, 115 in seeds, 116 in whole fruit ( minus seeds), 113 Rancidity in canned juice, 21 Red blotch—see Diseases and disorders Respiration, 46 during storage, 51 heat of, 47 Rootstock and soluble solids concentration, 60 and organic acids, 85 Seeds, 134 (see also Products and uses) and relation to endoxerosis, 134 Size and age—see Lemon fruit Soluble solids, 59 storage effect on, 58; concentration, 60: influence of rootstock on, 60 Specific gravity, 13 essential oil, 28 frozen fruit, 14 juice, 16 whole fruit, 13 Starch, 58 Stock feed—see Products and uses

• 163 Storage,5 and alternaría rot control, 51 and green mold, 55 and harvesting methods, 7 and hesperidin accumulation, 34 disorders during, 6, 57 effect of ethylene on, 54 effect on glycoside content in peel, 33 effect on juice quantity, 43 effect on respiration, 51 effect on soluble solids concentration in juice, 58 effect on sugar content, 70 ideal conditions of, 6, 59 Structure—see Lemon fruit Sugars, 64 and pH, 70 in frozen fruit, 69 in juice, 67 in peel, 64 storage effect on content, 70 Vitamins, 122 (see also Products and uses) A, source, 19 C, synthesis from galacturonic acid, 125 conditions controlling presence of, 124 functions in tissues, 127 kinds in juice, 123 " P " , 34 Water breakdown—see Diseases and disorders

In order that the information in our publications may be more intelligible, it is sometimes necessary to use trade names of products and equipment rather than complicated descriptive or chemical identifications. In so doing, it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned.

2 m - l l / 5 1 (8698) J B