in ripe fruits a part is in the form known as levulose or
fruit sugar, which is two and a half times sweeter than granulated
sugar. Sugars are valuable for heat-and fat-producing purposes, but not
for muscle repairing. Proteids are the muscle-forming nutrients. The
organic acids, as malic acid in apples, citric acid in lemons and
oranges, and tartaric acid in grapes, have characteristic medicinal
properties. The sugar, proteid, and acid content of some of our more
common fruits is given in the following table:[21]

COMPOSITION OF FRUITS

==============================================================
| WATER |PROTEIDS| SUGAR |ACID IN |KIND OF
| | | | JUICE | ACID
----------------|--------|--------|--------|--------|---------
|Per Cent|Per Cent|Per Cent|Per Cent|
Apples (Baldwin)| 85.0 | 0.50 | 10.75 | 0.92 |Malic
Apples, sweet | 86.0 | 0.50 | 11.75 | 0.20 |Malic
Blackberries | 88.9 | 0.90 | 11.50 | 0.75 |Malic
Currants | 86.0 | -- | 1.96 | 5.80 |Tartaric
Grapes | 83.0 | 1.50 |10 to 16|1.2 to 5|Tartaric
Strawberries | 90.8 | 0.95 | 5.36 | 1.40 |Malic
Oranges | 85.0 | 1.10 | 10.00 | 1.30 |Citric
Lemons | 84.0 | 0.95 | 2.00 | 7.20 |Citric
==============================================================

In addition to sugars, acids, and proteids, there are a great many other
compounds in fruits. Those which give the characteristic taste are
called essential or volatile oils.

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, an