Starchy foods form a large part of the ordinary diet of man; they are the chief source of the carbohydrates. Starch, unlike sugar, is insoluble but may be made to pass into a soluble form by dry-heating at high temperature, or by certain digestive ferments. The first bodies formed are known as dextrins, but ultimately a sugar (maltose) is produced. The alimentary starches may be said to comprise starch proper; dextrins or soluble starches; and glycogen or animal starch, which is stored up in the liver.

Source

Starch occurs widely in the vegetable kingdom, along with grape sugar. It is found in largest amounts in grains, seeds, roots and tubers. It is prepared for the market chiefly by mechanical means, being washed out of the finely cut vegetable substances. Its main commercial source is probably wheat, but it is also made largely from potatoes, rice, arrow-root, etc.

Description

In its pure state, i. e., when isolated from proteins, cellulose, gum, etc., starch is a shining white powder having a distinctive quality to the touch. Under the microscope it is found to consist of granules, which are insoluble in cold water. When heated to a high temperature, these granules undergo a certain amount of transformation into soluble starch and dextrin. Boiling the starch in water has the same results. The action of the group of ferments known as diastases is to transform starch successively into soluble starch, dextrin, and finally maltose (malt sugar).

Uses As Food

Starch is seldom used pure in dietaries, but with other food principles in the form of various flours and bread made from them,' or as breakfast cereals, legumes, potatoes, etc. The breads baked from wheat flour are among the most widely distributed foods.

Other Polysaccharides

Aside from starch and sugar the polysaccharides contribute but little to dietetic uses. Cellulose, the framework of plants, constitutes the largest proportion of their bulk. It is the principal part of the so-called "indigestible residue" of digestion; and hence the amount of the residue varies greatly with the nature of the food eaten. Without nutritive value, it is still believed to be of service as a stimulant to intestinal peristalsis, by acting as a gentle mechanical irritant; by helping to retain moisture and keep the feces soft; and by giving such bulk that the intestinal muscles can act to good advantage. When attacked by bacteria, it forms acids which are valuable checks to intestinal putrefaction. Unless it is desirable for some special reason to relieve the digestive tract of all work, a certain amount of cellulose should be included in the diet. In constipation the addition of some non-irritating form, as agar-agar has proved a successful therapeutic measure.

Gums, taken incidentally into the body, represent little or no nutritive value, and like cellulose act as "ballast".

Principles Of Cooking Starch

The principles involved in the cooking of starch are of two types - chemical and mechanical.