In making starch paste it is necessary to heat starch in water to at least 70° C.; the grains then swell to many times their original size, and if not separated from each other by an abundance of liquid, or some other substance such as fat or sugar, they stick together forming lumps. In a paste made below the boiling point of water the starch grains are unbroken, though much swollen, and on standing such a paste separates, the starch grains sinking to the bottom. At a boiling temperature the outer layer gradually dissolves and the starch makes a more homogeneous paste.

A starch paste is readily made by first mixing the dry starch with cold water, and then pouring the mixture into a large quantity of boiling water, and boiling for a few minutes. Thus prepared, the starch paste is semi-transparent, and free from lumps. It will mold or turn sour after a few days, unless preserved by some antiseptic, as borax or an essential oil.

When starch is cooked for some time it is so changed as to be more readily acted upon by the digestive juices. When heated with hydrochloric acid starch is hydrolyzed to mixtures of dextrin and maltose, and finally to glucose. Starch is also hydrolyzed by the ptyalin of the saliva producing dextrin and maltose, as in the previous case.

Test for Starch

To detect starch, boil the material to be tested for a few moments with water, cool, and add a drop or two of tincture of iodine, when a rich purple-blue color will be seen in case starch is present. Raw starch also gives the iodine reaction although more slowly, and different classes of raw starch react differently with iodine. The color fades from the iodine-starch solution when it is heated, but returns again on cooling.

n

Glycogen (C6H10O5) is sometimes called “animal starch," as it appears to have the same function in animals that starch has in plants. It is important as serving as a "storehouse" of reserve carbohydrates in fungi and those forms of plant life which cannot build up starch under the influence of chlorophyl.

Glycogen is a white powder, soluble in water, and may be extracted from muscles and liver. Oysters contain as much as 9 per cent. of glycogen. It is formed in some animals out of the sugars that are taken into circulation from the digestive tract, and acts as a reserve store of fuel for the maintenance of muscular energy.1 As would naturally be expected, the storage of glycogen in the animal body is promoted by rest and by liberal feeding, and the glycogen is rapidly used up during muscular work.

Dextrin (C6H1005) or (C6H1005).H2O, is not found ready formed in any quantity in raw food products, but is easily produced by the action upon starch of enzymes, acids or heat. It is sometimes called "British Gum," and may be made commercially by heating starch, either alone or with the addition of a small quantity of dilute mineral acid.

Dextrin as usually prepared, is a brownish substance, and differs from starch in being soluble in water. It may be precipitated from its solutions by alcohol. This carbohydrate is abundant in germinating cereals; it is formed on the outside of a loaf of bread during baking, and has a sweetish taste. Maltodextrin, the variety of dextrin found in malted cereals, is produced from starch by the action of the enzyme, maltose. It is believed to be a compound in which one molecule of maltose and two molecules of dextrin are in some way linked together. The specific kind of malto-dextrin formed in any case is largely dependent on the temperature maintained during the process of malting. Dextrin is found on the market in three forms, 2 a powder, a granular amorphous product, and a milky liquid. It is used as a substitute for gum acacia and other gums, in photography, calico printing, sizing paper, making of felt, and of printer's rolls and in the manufacture of ink. About 30,000 tons of dextrin are made annually in Germany. Both the imported and the domestic dextrin, before the war, sold in large quantities at from 5 to 6 cents a pound.

1 The Principles of Human Nutrition, Jordan, p. 73. 2 J. I. and Eng. Ch., Vol. 5, p. 77.

Inulin ((C6H10O5)n + H2O) is a starch-like substance found in solution in the sap of many plants. It occurs especially in the tubers of the dahlia and in the Jerusalem artichoke, and in smaller quantities in the potato, chicory, dandelion and elecampane, and also in some lichens.

When obtained from any of the above sources by methods similar to those used for separating starch, inulin is a white powder, which does not yield a blue color with iodine. It is slightly soluble in cold and readily soluble in hot water, and by hydrolysis with a mineral acid it is changed into fructose. It was formerly believed that this latter sugar was of value in the treatment of diabetes. The latter sugar is used by diabetic patients, as it apparently can be assimilated. Diastase has little effect upon inulin, and the ptyalin of the saliva does not convert it into sugar, as is the case with starch. It is probably changed into levulose in the stomach by the action of the hydrochloric acid of the gastric juice, and thus becomes digestible. An inulin bread and biscuit have been put upon the market, but however wholesome they may be for invalids, their flavor is not agreeable. It has been suggested that it might be possible to cultivate the artichoke or chicory in large quantities, and use the roots as a source of inulin for making commercial sirups.

Lichenin ((C6H10O5)n + H2O) is a starchy substance found in Iceland moss and algæ. Like starch it swells up with hot water and forms a jelly on cooling. This property makes it valuable for culinary purposes. The soluble portion is largely galactan, which by hydrolysis yields the sugar galactose (C6H12O6). From the physiological standpoint we learn that while there are enzymes or digestive ferments which convert starch into sugar, galactans are not digested in the body.

Gum, bassorin, cerasin, are amorphous carbohydrates, existing in many plants, which have the property of taking up water to form thick viscid products. They are usually soluble in water and insoluble in alcohol, and may be converted into sugars by heating with dilute acids. The most important of these are gum arabic, cherry-tree gum or cerasin and bassorin, found in

linseed and quince seed and many roots. Gum tragacanth is an important commercial product containing bassorin. The digestibility of gums has not been very thoroughly studied.

DISACCHARIDS

Disaccharids form a group including cane sugar, malt sugar and milk sugar (C12H22O11). When acted upon by weak acids or ferments they break up, by hydrolysis in such a way that cane sugar by taking up the elements of water yields glucose and fructose, malt sugar gives glucose, and milk sugar under similar conditions yields glucose and galactose.

Cane sugar (sucrose or saccharose) is by far the most important of these sugars. (See p. 101.) It is found in the juice and sap of certain plants, and is an important constituent of fruits. When heated it yields barley sugar and later caramel. One part of sugar is soluble in 0.46 parts of water at 77° F., and in 0.2 parts of boiling water.1

Malt sugar (maltose) is formed in the process of malting cereals, and is an intermediate product when starch is hydrolized by boiling with dilute acids as in the manufacture of commercial glucose. Maltose is formed by the action of the ptyalin of the saliva or the amylopsin of the pancreatic juice on starch or dextrin, and the maltose-splitting enzymes of the intestinal juice hydrolyze maltose to glucose.

Milk sugar (lactose) is found in the proportion of from 4 to 7 per cent. in the milk of all mammals. In sour milk the sugar has been converted by the lactic acid bacteria into lactic acid. Lactose reduces Fehling's solution,2 but has only seven-tenths the strength of dextrose in this respect. Milk sugar forms hard rhombic crystals, known as "sand sugar," which are soluble in six times their weight of cold water and two and a half times their weight of boiling water.

1 U. S. Pharmacopœia, p. 384.

2 A solution of copper sulfate and Rochelle salts, made strongly alkaline with sodium hydroxid.

MONOSACCHARIDS

In the group monosaccharids are included glucose, fructose, galactose, mannose, and sorbinose (C6H12O6). These sugars are all soluble substances, unaffected by digestive enzymes, and if not attacked by bacteria in the digestive tract they are absorbed and enter the blood current unchanged.1 They are readily susceptible to alcoholic fermentation and are utilized for the production of glycogen in the animal body and in the maintenance of the normal glucose content of the blood.

Glucose, grape sugar or dextrose, is abundant in fruit and plant juices, and in honey. It is manufactured commercially by the hydrolysis of starch. (See p. 122.) It has only two-fifths the sweetness of cane sugar.

Fructose, fruit sugar or levulose, occurs with glucose in plant and fruit juices and in honey. It serves, like glucose, for the production of glycogen in the liver, and the latter by hydrolysis yields glucose. It ferments with yeast and yields alcohol, but more slowly than dextrose. Fructose forms crystals of the rhombic system, but crystallizes with difficulty. The sugar in fruit, often called invert sugar, is usually a combination of glucose and fructose, and forms granular masses in raisins and other dried fruits.

Galactose, although not found free in nature, is produced by the hydrolysis of milk sugar either by acids or enzymes, and appears to promote the formation of glycogen in the animal body. Galactose is also produced by the hydrolytic cleavage of certain gums and of Carrageen moss. (See p. 305.)

Mannose is produced by the oxidation of mannite which occurs in manna, in celery and other roots and barks, but does not exist ready formed in nature. It is also a product of the fermentation of cane sugar, under certain conditions.

Sorbinose is the sugar found in the juice of the fruit of the mountain ash and the service tree.

1 The Chemistry of Food and Nutrition, Sherman, p. 6.