5. The composition of all cereals is similar, yet each one has its
distinguishing feature. While all the five food substances--water,
mineral matter, protein, fat, and carbohydrate--are to be found in
cereals, they occur in different quantities in the various kinds. Some
contain large quantities of protein and others practically none, and
while certain ones have considerable fat others possess comparatively
small quantities. A characteristic of all cereals, however, is that they
contain a large amount of carbohydrate and a small amount of water. It
is well to remember, though, that while the food substances of cereals
are found in sufficient quantities to sustain life, they will not permit
a person to live for long periods of time exclusively on this form of
food. Likewise, it will be well to observe that the foods made from a
certain grain will be quite similar in composition to the grain itself;
that is, any change in the composition of the foods must be brought
about by the addition of other substances.
6. All grains are similar in general structure, too. The largest
proportion of carbohydrate lies in the center, this substance growing
less toward the outside of the grain. The protein lies near the outside,
and grows less toward the center. Fat is found in small amounts
scattered through the entire grain, but most of it is found in the
_germ,_ which is a tiny portion of the grain from which the new plant
sprouts. The mineral matter of cereals is found chiefly just inside the
bran, or outer covering, so that when this covering is removed, as in
the process of preparation for food, a certain amount of mineral matter
is generally lost.
7. PROTEIN IN CEREALS.--The cereals are essentially a carbohydrate food,
but some also yield a large proportion of protein. In this respect they
differ from the animal foods that produce the principal supply of
protein for the diet, for these, with the exception of milk, do not
yield carbohydrates. The grain that contains the most protein is wheat,
and in the form in which protein occurs in this cereal it is called
_gluten,_ a substance that is responsible for the hardness of wheat. The
gluten, when the wheat is mixed with water or some other liquid, becomes
gummy and elastic, a fact that accounts for the rubbery consistency of
bread dough. Cereals that contain no gluten do not make bread
successfully. Next to wheat, rye contains protein in the greatest
amount, and rice contains the least. Although protein is the most
expensive of the food substances, the kind of protein found in cereals
is one of the cheaper varieties.
8. FAT IN CEREALS.--The fat of cereals helps to contribute to their
heat-and energy-producing qualities, and, besides, it is one of the
cheaper sources of this food substance. Of the eight grains, or cereals,
used as food, oats and corn contain the most fat, or heat-producing
material. The oil of corn, because of its lack of flavor, is frequently
used in the manufacture of salad oil, cooking oil, and pastry fat. The
fat that occurs in cereals becomes rancid if they are not carefully
stored. In the making of white flour, the germ of the wheat is removed,
and since most of the fat is taken out with the germ, white flour keeps
much better than graham flour, from which the germ is not abstracted in
the milling process.
9. CARBOHYDRATE IN CEREALS.--The food substance found in the greatest
proportion in cereals is carbohydrate in the form of starch. Cereals
contain many times more starch than any of the other food substances,
rice, which is fully three-fourths starch, containing the most, and
oats, which are less than one-half starch, the least. Starch is
distributed throughout the grain in tiny granules visible only under the
microscope, each being surrounded by a covering of material that is
almost indigestible. In the various grains, these tiny granules differ
from one another in appearance, but not to any great extent in general
structure, nutritive value, or digestibility, provided they are cooked
thoroughly. The large amount of carbohydrate, or starch, in cereals
explains why they are not hard to digest, for, as is well known, starch
is more easily digested than either protein or fat. This and the fact
that some grains contain also a large amount of fat account for the high
energy-producing quality of cereals. While it is safe to say that
cereals are chiefly valuable for their starch, the tissue-building
material in some grains, although in small proportion, is in sufficient
quantity to place them with the protein foods.
10. MINERAL MATTER IN CEREALS.--Cereals contain seven or eight of the
minerals required in the diet. Such a variety of minerals is sure to be
valuable to the human body, as it is about one-half of the whole number
required by the body for its maintenance. Since, as has already been
explained, much of the mineral matter lies directly under the coarse
outside covering, some of it is lost when this covering is removed. For
this reason, the grains that remain whole and the cereal products that
contain the entire grain are much more valuable from the standpoint of
minerals than those in which the bran covering is not retained. If a
sufficient percentage of minerals is secured in the diet from
vegetables, fruits, and milk, it is perhaps unnecessary to include whole
cereals; but if the diet is at all limited, it is advisable to select
those cereals which retain the original composition of the grain.
11. WATER IN CEREALS.--Cereals contain very little water in their
composition. This absence of water is a distinct advantage, for it makes
their nutritive value proportionately high and improves their keeping
quality. Just as the strength of a beverage is lowered by the addition
of water, so the nutritive value of foods decreases when they contain a
large amount of water. On the other hand, the keeping quality of cereals
could scarcely be improved, since the germs that cause foods to spoil
grow only in the presence of water. This low proportion of water also
permits them to be stored compactly, whereas if water occurred in large
amounts it would add materially to their bulk.
12. CELLULOSE IN CEREALS.--In addition to the five food substances that
are found in all cereals, there is always present another material known
as cellulose, which, as is pointed out elsewhere, is an indigestible
material that occurs on the outside of all grains, as the bran covering,
and covers the starch granules throughout the inside of the grain. In
fact, it forms a sort of skeleton upon which the grains are built. As
long as the cellulose remains unbroken, it prevents the grain from being
digested to any extent. However, it forms a valuable protective covering
for the grain and it has a certain value, as bulk, in the diet, a fact
that is ignored by some persons and overrated by others. It is well to
include at least some cellulose in cereal foods when they are taken in
the diet, because its presence tends to make food less concentrated.
13. TABLE SHOWING COMPOSITION OF CEREALS.--Not all grains, or cereals,
contain the same amount of food substances and cellulose; that is, while
one may be high in protein it may be lacking in some other food
substance. The relation that the various grains bear to one another with
regard to the food substances and cellulose is clearly set forth in
Table I. In this table, under the various food substances and cellulose,
the grains, with the exception of millet, are mentioned in the order of
their value, ranging from the highest down to the lowest in each of the
food substances and cellulose. Thus, as will be seen, wheat is highest
in protein and rice is lowest, oats are highest in fat and rye is
lowest, and so on. Also, as will be observed, while wheat is highest in
protein, it is, as compared with the other cereals, sixth in fat, fourth
in carbohydrate, fourth in cellulose, and fifth in mineral matter. In
this way may be compared all the other cereals to see in just what way
they are of value as a food.