20. TABLE SHOWING COMPOSITION AND FOOD VALUE OF FRUITS.--Just as fruits vary in their composition, so do they vary in their food value. This fact is clearly shown in Table I, which gives the percentage of food substances contained in different fruits and the food value per pound, in calories, that these fruits contain. As in the table showing the composition and food value of vegetables given in Vegetables, Part 1, the figures in this table are taken from Atwater's Table of American Food Materials and refer to the edible part of the material. Reference to Table I, as progress is made with the study of fruits and their preparation, will be of much assistance in learning the place that fruits occupy in the dietary.
FOOD VALUE OF FRUITS
21. EFFECT OF RIPENESS ON FRUITS.--There is a very marked difference between ripe and green fruits as to their composition, flavor, texture, palatability, and digestibility. Green fruits, containing more acid than ripe ones, serve some purposes for which ripe fruits of the same variety cannot be used so well. For instance, a very much better jelly can be made from grapes that are not entirely ripe than from those which have completely ripened. Green fruits contain less sugar than do ripe ones, and so they are more sour to the taste. In some cases, the carbohydrate found in green fruits is partly in the form of starch, which in the process of development is changed to sugar. The cellulose of green fruits, especially that distributed throughout the pulp of the fruit itself, is usually tougher and harder than that which is found in the same fruit after it has ripened.
22. DIGESTIBILITY OF FRUITS.--The ripeness and freshness of fruits determine their digestibility to a great extent, but the peculiarities of each person have much to do with this matter. Many times a particular fruit will agree with almost every one but a few exceptional persons, and, for no apparent reason except their own peculiarities of digestion, it disagrees very badly with them. Abnormal conditions of the alimentary tract, however, cannot be taken into consideration in a general discussion on the digestibility of foods, for it is a subject that cannot be treated except from a dietetic standpoint. A safe rule to follow when a fruit is found to disagree with a person is to omit it from that person's diet. This need not prove a hardship, for the wide range, or variety, of fruits makes it possible to find one or more kinds that will agree with each person.
23. As has been explained, sugar is the food material from which the nutritive value of fruits is obtained. With the exception of a few predigested foods, manufactured in such a way that they can be digested easily, this sugar is probably the most easily digested form of food that can be obtained. This substance, being held in solution in the fruit juices, which are encased in a cellulose covering, depends to some extent for its digestion on the hardness of the cellulose. When this covering is old and hard or green and tough, as the case may be, it is difficult for the digestive juices to break through and attack the sugar contained inside. As this difficulty is not encountered when fruit is fresh and ripe, its freshness and ripeness become important factors in digestibility. Cooking is also an important factor because it softens the cellulose, but there are certain other changes made by cooking that must be taken into consideration as well.
24. EFFECT OF COOKING ON FRUIT.--Cooking affects fruits in numerous ways, depending on the condition of the fruit itself, the method used, and the length of time the heat is applied. When fruits are cooked in water or in a thin sirup, the cellulose becomes softened. On the other hand, if they are cooked in a heavy sirup, as, for instance, in the making of preserves, the cellulose becomes hardened and the fruit, instead of breaking up, remains whole or nearly so and becomes tough and hard in texture. The addition of quantities of sugar, as in the latter case, besides helping to keep the fruit whole, increases its food value.
25. Another change that usually takes place when fruit is cooked is in its flavor. This change is due either to an increase in the acid contained in the fruit or to a decrease in the amount of sugar. Some authorities believe that cooking increases the amount of acid, while others hold the view that, when fruit is cooked without removing the skins and seeds, the acid contained in the seeds and skins and not noticeable when the fruit is fresh, is released during the cooking. Such is undoubtedly the case with plums. The change that is brought about in the sugar by the cooking of fruits consists in changing the cane sugar into levulose and dextrose, which are not so sweet. This change accounts for the fact that some cooked fruits are less sweet than others, in spite of the fact that the acid does not seem to be increased.
26. In addition to producing certain changes in fruit, cooking, if done thoroughly, renders fruits sterile, as it does other foods; that is, it kills any bacteria that the fruits may contain. Advantage of this fact is taken when fruits are canned for future use. Although most persons prefer raw fruit to that which is cooked, there are some who object to eating this food raw, but who are not always certain as to the reason for their objection. Like other raw foods, fruits in their fresh state contain vitamines; that is, a substance that helps to keep the body in a healthy, normal condition. These are found to some extent in cooked fruits, but not in the same quantity as in raw ones; consequently, as much use as possible should be made of raw fruits in the diet.