XVII. THE RESEARCH FIELD IN CITRUS CHEMISTRY
L.
W. GAD DUD^, AGRICULTURAL E X P E ~ NSTATION, T UNIVERSITYOB FLORIDA, GAI~SVILLE, FWRIDA
The research problems in the field of citrus chemistry may be classed under two general heads-immediately practical problems and fundamental, or more remotely practical, problems. Obviously the line of demarcation between the two types of problems is not sharp; many problems are boundary line problems. Nevertheless, certain questions are of great interest in an industrial way and consequently funds are available for the financing of research on these questions. On the other hand, a number of questions are a t present purely of academic interest and means for research along these lines are not so readily at hand. In the latter category are those problems dealing with the chemical nature of various constituents of the citrus fruits. The essential oils of the orange and of the lemon have received considerable attention in the past, but the oil of the grapefruit, tangerine, and kumquat have a t best a scanty background of research literature. These oils are at present of comparatively little commercial importance and consequently there is little incentive for their study except that of academic curiosity. However, it has frequently happened that the commercial significance of certain materials was greatly magnified by a more thorough knowledge of the nature of those materials, and this knowledge has more often than not been attained through the efforts of the academic chemist. Among the carbohydrate constituents of the citrus fruits, the pectins deserve particular attention. Do the pectins from different natural sources possess identical constitutions? Can the pectins be made to yield Just what derivatives as useful as those of their near relative-cellulose? factor in the pectin structure determines its value as a jellifying agent? These and many other questions on the chemistry of the pectins await solution. Closely related to the carbohydrate constituents are the glucosides, and these also offer abundant material for research. Their chemical nature and physiological effect, if any, should be at least of academic interest. Can naringenid, hesperitin, or other citrus glucoside products be utilized in any manner which would make their extraction from citrus residues profitable? Of more than academic interest, however, are numerous problems connected with the utilization of waste products. The canning of grapefruit leaves enormous quantities of waste peels which conceivably offer 2347
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OCTOBBR, 1930
raw materials for the production of pectin and grapefruit oil. The possibility of utilizing this raw material for the production of grapefruit oil, pectin, stock feed, and fertilizer is distinctly worthy of investigation. Methods of extraction, methods of assaying the raw material, evaluation of the products for their respective uses, and the enlargement of the possible uses to which the products can be put are all urgent problems for study. The preservation of orange and grapefruit juice over extended periods of time is an exceedingly rich field for work. In the past, the preservation of the latter juice seems to have met with more success than that of orange juice. A careful study of the factors affecting the development of offflavors in the preserved orange juice and the search for methods for coutrol of these factors appears to be a field in which success will be accompanied by pecuniary reward. Verging on the field of plant physiology, are found other problems dealing with chemical reactions in the living plant. I t has been reported that arsenical sprays cause deterioration in the flavor of citrus fruits, due to decrease in the sugar-acid ratio of the ripe fruit. A comprehensive study of the physiological effects of various spray materials is thus of considerable economic importance to the citrus grower. The employment of ethylene in the ripening of citrus fruits may also he mentioned as deserving of more investigation, since in some quarters this process is considered as still in a problematic stage. It is obvious that the various questions suggested above cannot be fully discussed in a general paper without throwing undue emphasis on some one phase. It is hoped, however, that the mention of certain problems and the preseutmeqt of the actual existence of important problems in the field of citrus chemistry will direct the attention of chemists toward the study of the citrus fruits.
