58. Food Value.—When the nutrients alone are considered, fruits appear to have a low food value, but they should not be judged entirely on this basis, because they impart palatability and flavor to other foods and exercise a favorable influence upon the digestive process. In the human ration fruits are a necessary adjunct.
59. Apples.—Apples vary in composition with the variety and physical characteristics of the fruit. In general they contain from 10 to 16 per cent of dry matter, of which 75 per cent, or more, is sugar or allied carbohydrates. Among the organic acids malic predominates, and the acidity ranges from 0.1 to 0.8 per cent. Apples contain but little protein, less than 1 per cent. There is some pectin, or jelly-like substance closely related to the carbohydrates. The flavor of the apple varies with the content of sugar, organic acids, and essential oils. During storage some apples appear to undergo further ripening, resulting in partial inversion of the sucrose, and there is a slight loss of weight, due to the formation of carbon dioxide. The apple is an important and valuable adjunct to the dietary.[[22]]
| Fig. 12.—Graphic Composition of Apple. | Fig. 13.—Graphic Composition of Orange. |
60. Oranges contain nearly the same proportion of dry matter as apples, the larger part of which is sugar. Citric acid predominates and ranges in different varieties from 1 to 2.5 per cent. The amounts of protein, fat, and cellulose are small. In some varieties of oranges there is more iron and sulphur than is usually found in fruits. All fruits, however, contain small amounts, but not as much as is found in green vegetables. The average composition of oranges is as follows:
| Physical Composition | Chemical Composition of Edible Portion | ||||
|---|---|---|---|---|---|
| Per Cent | Per Cent | ||||
| Rind | 20 to 30 | Solids | 10 to 16 | ||
| Pulp | 25 to 35 | Sugars | 8 to 12 | ||
| Juice | 35 to 50 | Citric acid | 1 to 2.5 | ||
| Ash | 0.5 | ||||
61. Lemons differ from oranges in containing more citric acid and less sucrose, levulose, and dextrose. The ash of the lemon is somewhat similar in general composition to the ash of the orange, but is larger in amount. The average composition of the lemon is as follows:
| Physical Composition | Chemical Composition of Edible Portion | |||
|---|---|---|---|---|
| Per Cent | Per Cent | |||
| Rind | 25 to 35 | Solids | 10 to 12 | |
| Pulp | 25 to 35 | Sugars | 2 to 4 | |
| Juice | 40 to 55 | Citric acid | 6 to 9 | |
62. Grape Fruit.—The rind and seed of this fruit make up about 25 per cent, leaving 75 per cent as edible portion. The juice contains 14 per cent solids, of which nearly 10 per cent is sugar and 2.5 per cent is citric acid. There is more acid in grape fruit than in oranges and appreciably less than in lemons. The characteristic flavor is due to a glucoside-like material. Otherwise the composition and food value are about the same as of oranges.
