1. Starch

The chemical formula of starch and other polysaccharids is written (C6H10O5)n. This means that the proportion of the elements is according to the figures given, but the number of atoms that are supposed to be combined is many times greater than five, and is not accurately known. This is purely theoretical, and of no practical importance, except that it shows that the polysaccharid is capable of being digested or broken up into many simple carbohydrate compounds.

Starch is the most abundant carbohydrate known. It is the chief constituent of all cereals, and is found in large quantities in green fruits and tuberous plants. Starch occurs in small granules, varying greatly in size in different foods.

Potatoes are composed chiefly of starch and water. The starch grains of potatoes can almost be distinguished with the naked eye. These starch granules are not atoms or molecules in the chemical sense, but are small receptacles in which starch has been deposited by the growing plant. When cooked or boiled in water these starch grains swell into a mushy, pasty or gelatinous mass; when cooked in dry heat until they begin to turn brown, they are changed into a compound related to the gum group, known as dextrin.

Starch does not dissolve in water as do sugars. If starch is treated with digestive fluids, such as saliva, or with certain acids, it goes through a complex process of digestion in which it is first turned into soluble starch, then into the various forms of dextrin or gums, and finally into maltose or malt-sugar.

Sources of starch.

Potato starch.

Corn-starch, treated with weak sulfuric acid, changes the starch into glucose. The ordinary glucose or corn-sirup is not all changed by this process, into pure glucose, but contains some maltose and other gummy compounds; hence it will not crystallize or granulate into pure sugar. After the acid has changed the starch into glucose it (the acid) is neutralized with an alkali. A crude compound is thus formed, which settles to the bottom of the tank, and from which the glucose can be easily separated. Commercial glucose is now very extensively used in the manufacture of various food products, especially confectionery. Pure glucose is a wholesome food, but there is some danger that the commercial product may (due to carelessness in manufacturing, or to the use of cheap and impure acid) contain various mineral poisons. Government testing of glucose and similar manufactured products is, in the writer's opinion, fully as essential as the government inspection of packing-house products.

Solubility of starch.

How corn-starch is changed into glucose.

Just as glucose may be manufactured from starch treated with dilute acids, so maltose may be made by treating starch with malt. The brewing of beer depends upon the chemical changes induced in starch by malt. Barley is ordinarily used for this purpose. The barley is sprouted in a warm, damp room, and a process of starch digestion begins, which is necessary in order that the young barley sprouts may grow. This changes the starch into maltose. The digestive principle developed in the barley-malt may be utilized to malt other grains by mixing them with the sprouted barley.

How starch is changed into maltose.

If this process of malting is stopped at the proper time, and the sugar dissolved, and extracted, a product is formed consisting chiefly of the sugar maltose. This is the basis of malt extract, malt honey, and many similar foods put on the market, which are claimed by the manufacturers to have wonderful dietetic and curative values.

2. Glycogen

Glycogen is commonly called animal-starch. It exists in the liver in small quantities. All carbohydrates are digested in the alimentary canal and absorbed into the blood in the form of simple sugars of the glucose group. When these sugars reach the liver they are again built up into a complex carbohydrate very similar to starch in composition. This glycogen or animal-starch is stored in the liver until the body has need of it, when it is changed into glucose and given back to the body in the form of energy. (See "Metabolism of Carbohydrates," Lesson VI (Chemistry Of Metabolism), p. 202).

Maltose in foods.

Glycogen - how formed and where stored.

3. Cellulose

Cellulose, from the standpoint of human nutrition, is not a food product, being insoluble by the digestive juices, but it is very important in the digestion and the alimentation of other foods. Its chief purpose is to excite stomach and intestinal peristalsis. All plant products in their natural form contain some cellulose, though the percentage is very small in such grains as rice and barley. The bran of wheat or of corn is chiefly cellulose. Wood is almost pure cellulose.

Cellulose can be digested by strong acids into simple carbohydrates, in the same way that starch may be. Sugar can be manufactured from wood or rags, but the process is yet too expensive to be applied commercially. Some of us may live to see the time when the chief food of mankind will be manufactured from scrap lumber and waste paper. Bacteria have the power of digesting cellulose. The bacterial action or fermentation in the human intestines may cause a small amount of cellulose to be digested, but the quantity is of no consequence from a nutritive point of view.

Cellulose - its purpose, source, and Importance.

4. Gums

The gums include a group of rather complex carbohydrates which are intermediate between starches and sugars. From plants are derived many varieties of gums which have various commercial uses in the market, such as gum arabic.

I have already spoken of the formation of dextrin from starch. Dextrin has no particular dietetic qualities that do not exist in starch. It is, in fact, starch arrested at an intermediate point of digestion.

Pectins are a group of gummy substances found in fruits, especially green fruits which are in the process of being formed into sugar. These pectins form the basis of fruit jellies. Green grapes, as every housewife knows, will make better jelly than ripe grapes. This is because the pectins in ripe grapes have been transformed into sugar. The pectins in fruit are in most cases wholesome enough, though it would seem the better part of wisdom to eat all fruits in the ripened state, after Nature has completed her work.

5. Inulin

Inulin is a compound closely related to starch, and upon digestion with acids, yields levulose just as starch yields glucose. It is of no particular interest to the food chemist, as it exists in but very small quantities in starch, and has no distinct dietetic value.

Pectins in fruits.