CHAPTER VI
LEGUMES AND NUTS
84. General Composition of Legumes.—Peas, beans, lentils, and peanuts are the legumes most generally used for human food. As a class, they are characterized by high protein content and a comparatively low per cent of starch and carbohydrates. They contain the largest amount of nitrogenous compounds of any of the vegetable foods, and hence are particularly valuable in the human ration as a substitute for meats.[[32]] For feeding animals the legumes are highly prized, particularly the forage crops, clover and alfalfa. These secure their nitrogen, which is the characteristic element of protein, from the free nitrogen of the air, through the workings of bacterial organisms found in the nodules on the roots of the plants. The legumes appear to be the only plants capable of making use of the nitrogen of the air for food purposes.
85. Beans contain about 24 per cent of protein and but little fat, less than is found in any of the grain or cereal products. The protein of the bean differs from that of cereals in its general and structural composition. It is a globulin known as legumin, and is acted upon mainly by ferments working in alkaline solutions, as in the lower part of the digestive tract. Beans have about the same amount of ash as the cereals, but the ash is richer in potash and lime.
Fig. 19.—Graphic
Composition of Beans.
Hacked Part Indigestible.
86. Digestibility of Beans.—Beans are usually considered indigestible, but experiments show they are quite completely digested, although they require more work on the part of the digestive tract than many other foods. The digestibility was found to vary with individuals, 86 per cent of the protein being digested in one case, and only 72 per cent in another. The protein of beans is not as completely digested as that of meats. When beans were combined with other foods, forming a part of a ration, they were more completely digested than when used in large amounts and with only a few other foods. The presence of the skin is in part responsible for low digestibility. When in the preparation of beans the skins, which contain a large amount of cellulose, are removed, the beans are more completely digested. By cooking from twenty minutes to half an hour in rapidly boiling water containing a small amount of soda, the skins are softened and loosened and are then easily removed by rubbing in cold water. Some of the soda enters into combination with the legumin. Along with the skins a portion of the germ is lost. The germ readily ferments, which is probably the cause of beans producing flatulence with some individuals during digestion. After the skins are removed the nutrients are more susceptible to the action of the digestive fluids. Experiments show that 42 per cent of the protein of baked skinned beans is soluble in pepsin and pancreatin solutions, while under similar conditions there is only 3.85 per cent of the protein soluble from beans baked without removal of the skins.
87. Use of Beans in the Dietary.—There is no vegetable food capable of furnishing so much protein at such low cost as beans; from a pound costing five cents about one fifth of a pound of protein and three fifths of a pound of carbohydrates are obtained. Beans can, to a great extent, take the place of meats in the dietary. There is more protein in beans than in beef. Four ounces of uncooked beans or six ounces of baked beans are as much as can conveniently be combined in the dietary, and these will furnish a quarter of the protein of the ration. In the case of active out-of-door laborers over a pound of baked beans per day is often consumed with impunity.
