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.
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