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Chapter XIII

FOODS SUPPLYING MINERAL SALTS AND ORGANIC ACIDS, MORE PARTICULARLY FRUIT THE foods that supply us with mineral salts and organic acids are found largely in the vegetable kingdom. Some of these are in the form of roots, leaves, blossoms and stems of plants; others are the seed vessels of the plants, and still others are the fleshy coverings of the seeds intended by nature as a protection for the latter until maturity, or for the early sustenance of the young plant which sprouts from the seed. We speak of these foods as fruits and vegetables. Properly, however, all the seed vessels are fruits, while the others are vegetables, but we are not accustomed to think of a squash or a tomato as a fruit, and so the distinction we make between fruits and vegetables seems to be largely a matter of custom. COMPOSITION AND FOOD VALUE OF FRUITS Most fresh fruits contain a large proportion of water, from eighty to ninety per cent, being not an unusual proportion. There is also considerable cellulose in fruit; this, with other starch present in unripe fruit, is largely changed by the ripening process into sugar and gums. One of these gums, pectin, corresponds to the gelatine in meats. It is this gum that causes fruit juice to jelly when it is cooked with sugar.

The quantity of proteid in fruit is very small; as a rule less than one per cent. is found.

From a dietetic point of view fruits are valuable on account of the relatively large proportion of mineral salts and organic acids which they contain; of the salts, potash, found also in many vegetables, is the most important. The organic acids in fruits (tartaric, malic, citric, etc.) impart to them an agreeable acid flavor and tend to keep the blood in an alkaline condition, a state on which good health depends. The water in fruits may be considered as distilled, than which no better source of pure water exists. DIGESTIBILITY OF FRUIT The digestibility of fruit depends largely upon the nature of the variety and its degree of ripeness. An apple has a firmer cellular structure than a peach and thus the latter is the more easily broken up and acted upon by the digestive fluids. Thus the peach is very properly called "the children's fruit." As sugar is more easily digested than starch, and as the starch and cellulose in ripe fruit have been largely changed to sugar, ripe fruit is more easily digested than that which has not reached this condition. When the banana is in a fit condition to eat (uncooked) the skin has become dark, at least in spots, and the pulp is dry and mealy. Bananas left in a paper bag will ripen more quickly than when left uncovered in the light. Cooking is a ripening process, and bananas, pears and apples, not sufficiently ripe to eat raw, are palatable and wholesome, cooked.