The Nutritive Value of Fruits I. General Considerations ALMOST all the known dietary surveys suggest that an increased consumption of fruit would be desirable. This indication appears to be easy of attainment, but peak consumption seems definitely related t o price considerations governing the availability of this class of foodstuffs, especially to the nndernourished and to the poor. At one time the arrival of the berry season was observed as a distinct date on the calendar similar to the closing of school and the beginning of the summer holidays, but now berries of all kinds are available the year round owing t o modern methods of refrigeration and distribution of such foods. It can be confidently predicted that further advances in the method of transportation will be made, particularly by air. The fruits are usually divided into different classes, such as berries, citrus, drupes, grapes, melons, pomes, and tropical. The more highly prized among these classes have flavors making them especially attractive to the palate. The characteristic fruity flavor is caused by alcohols, aldehydes, acids, esters, ethers, or terpenes, or a mixture thereof. Thus, the odor and taste of bananas are brought about by amyl acetate, and those of grapes by methyl anthranilate. As a class the fruits are juicy, with a high water content, sugar. and acid. Some, such as the date and banana, are so sweet ss to mask any tart flavor, while other less-known varieties, as the bilimbi and carambola, are so tart as to mask any sweetness, and for this reason find use in pickles and preserves. During the growing and ripening process, the fruits contain variable quantities of starch. As they approach maturity the starch is converted into sugars, followed by an inversion of sucrose, and a decrease in acid content. Avocados and (green) olives are exceptions as they contain relatively large amounts of oil rather than sugar and starch, and the seeds of other fruits are said t o be more often oily than starchy. Degree of maturity is important, for unripe fruit may cause stomach irritation by excessive acid, while, where overripe, sweet fruits msy produce an abnormal fermentation. The fruits, in general, possess the nutritive virtues of vegetables, containing ascorbic acid (vitamin C) in variable quantities, ranging from the citrus group that is especially valuable in this regard, through and including apples, grapes, and pears. which are rather low in this factor. Because the latter are customarily eaten raw, they often become significant as a source of ascorbic acid. Considerable care must be taken in the processing of fruits so as to retain their natural content of this vitamin. Careless handling may produce a loss in antiscorbutic effect because the cyclic molecular structure of the vitamin is changed hy an opening up of the lactone ring. This deterioration in potency is hastened in alkaline solution and by activity of enzymes, particularly the oxidases. Other nutritive values in fruits are vitamin A, as carotene, its provitamin (apricots, cantaloupes, yellow peaches, and pnmes). thiamine (prunes), riboflavin (prunes and raisins), niacin (dates, figs, and peaches), inositol, and choline. The mineral content of fruits is, of course, low because of their high water content. The mineral content can be significant, however, based on energy values, as per 100 calories. Several fruits are significant sources of calcium (figs, oranges, prunes, raspberries, and strawberries), iron (apricots, bananas, dates, figs, grapes, prunes, raisins, raspberries, and strawberries), and copper (prunes). I n simple
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In addition to their vitamin and mineral contents, the fruits furnish bulk t o the diet, producing a mild, frequently desirable, laxative effect and fias). Their alkalizine uro~ertiesare well known. and. with the e&otion of cranberriei. ilums. and prunes which form hippuric acid.in the body, they all increase the alkalinity of the urine; consequently they are of value in excessive acid conditions. While research on fruits, like that on vegetables, is still in its adolescent stage, several recent investigations mark new progress. Various methods of storing citrus fruits have been employed. As a result of such experiments high humidity and control of oxygen and carbon dioxide have become important. Washing fruits before storage apparently decreases their keeping quality. The drying of fruits has assumed new importance. Apples. apricots, peaches, prunes, raisins, and currants, in dried form, are now in heavy demand by the Armed Forces and our Allies, because they are relatively nonperishable and require less space in shipping. Baker and confectioners are using tremendous quantities of dried fruits in their products. The browning or discoloration of cut or sliced fruit is now controlled by thiourea, a substance of low toxicity. I n addition t o the protection afforded against destruction of naturally occurring color pigments by enzymes, thiourea possesses valuable properties in protection against loss of ascorbic acid. The treatment of fruit with sulfur dioxide during drying also is said t o retard the loss of color and of ascorbic acid. Certain hailed vegetable juices, as those from cabbage and potatoes, are reported to be active in this respect. Certain fruits, as the papaya and pineapple, contain powerful digestive properties awing to the presence of a proteolytic enzyme, papain. Extracts of this enzyme are employed to alleviate dyspepsia and t o "tenderize" meats and casings. Papain also finds application in the brewers' trade, in the tanning of leather, and in the prevention of shrinkage in wool. Numerous fruits are good sources of pectin, being useful for jelly making. Pectin in commercial form is commonly obtained from citrus albedo and apple pomace. Citrus residues are also employed as stock feed. The number of useful industrial compounds obtainable from fruits is increasing. A discussion of fruits is not complete without mention of the growth of the fruit juice industry. Several years ago the only preserved fruit juice of commercial importance was that of the grape. Small quantities of other fruit juices were packed but the output was small. In 1926 canned grapefruit juice was fist packed commercially. Its popularity has increased each year. Along with grapefruit juice, pineapple juice has shown a steady growth, and large quantities of apple, orange, and grape juices are packed. Other products are cherry, cranberry, currant, lemon, loganberry, papaya, plum, pomegranate, prune, raspberry, strawberry, tangerine, and youngberry juices, and certain pulpy fruit beverages called "nectars" that are usually prepared from apricots, peaches, and pears. Many combinations of different fruit juices and nectars are possible. These fruit juices and nectars generally possess the nutritive virtues of the fruit from which they were made.-Reprinted from Nutritional Observatofy, 6,22 (1945).
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