The Lemon Fruit: Its Composition, Physiology, and Products

By Elbert T. Bartholomew

This title is part of UC Press's Voices Revived program, which commemorates University of California Press’s mission to seek out and cultivate the brightest minds and give them voice, reach, and impact. Drawing on a backlist dating to 1893, Voices Revived makes high-quality, peer-reviewed scholarship accessible once again using print-on-demand technology. This title was originally published in 1951.

• Language: English
• Publisher: University of California Press
• Release date: Nov 15, 2023
• ISBN: 9780520346994

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University of California Press

Berkeley and Los Angeles

California

Cambridge University Press

London, England

Copyright, 1951, by

The Regents of the University of California

PRINTED IN THE UNITED STATES OF AMERICA

BY THE UNIVERSITY OF CALIFORNIA PRESS

DESIGNED BY A. R. TOMMASINI

PREFACE

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 literature.¹ The 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 ¹ See Literature Cited for citations, referred to in the text by author and date.

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 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 1

CONTENTS 1

Chapter I GENERAL INFORMATION

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

Chapter II COMPOSITION AND PHYSIOLOGY

Specific Gravity

Color in Peel

Lipids

Essential Oil

Hesperidin

Limonin and Nomilin (Bitter Principles)

Moisture

Storage, Effect on Juice Quantity

Respiration

Starch

Soluble Solids

Sugars

pH

Organic Acids and Buffer Properties

Polysaccharides

Pentosans

Pectin

Cellulose and Hemicellulose

Proteins

Glutathione

Enzymes

Vitamins

Inorganic Constituents

Seeds

Chapter III PRODUCTS AND THEIR USES

Whole Fruit

Peel

Juice

Seeds

LITERATURE CITED

AUTHOR INDEX

SUBJECT INDEX

Chapter I

GENERAL INFORMATION

Origin and History

THE LEMON 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…."

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 Columbus 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:

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

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 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 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 2232 to 2%2 in diameter, but the ones most commonly used are 2%2", 2%2 and 2%2 in diameter. The name of the sizing ring is indicated by its number of 32nds of an inch in excess of 2 inches, thus the five rings just mentioned would be called Nos. 2,9, 6, 7 and 8 picking rings. The size of the ring used for any one picking depends on local conditions and on the market’s demand for fruit. When brought to the packinghouse the fruits are segregated according to color. The color designations may include all or part of the following: dark green, green, light green, silver, light silver, light yellow, yellow, and dark yellow (tree ripe). A lemon is said to be tree ripe when it has remained on the tree for at least several weeks after it has changed from light yellow to dark yellow in color. Some fruits are picked before they have reached the usual picking size. They are those that have turned light silver to dark yellow and have stopped or practically stopped growing. Sizes smaller than will pack 588 fruits (1.750 inches in diam.) to the box are usually sent to the products plant.

All lemon fruits used in the experiments described on the following pages were commercially mature, unless specially designated as immature, young, very young, or very small.

Storage

The nature of the lemon fruit is such that it can be safely stored much longer than other commercial species of citrus. Since lemons are usually picked according to size rather than color they may be green when put into the storage rooms. The demands of the market usually determine the length of time that they are kept in storage. If the demand is strong, a portion or all of the green lemons picked and taken to the packinghouses are treated at once with ethylene gas which causes them to change from green to yellow in color within a few days, generally 5 to 7. They are then ready to be placed on the market. If there is no immediate demand, the lemons are placed in storage rooms where, after several weeks, they become yellow without the ethylene treatment. Citrus fruits themselves give off a small amount of ethylene while in storage but probably not enough to cause degreening of the fruit (see section on Respiration, p. 46).

When lemon fruits are kept in storage over extended periods, sometimes 3 to 4 months or longer, every precaution