Foods, their selection and preparation

forms, and vitamin A obtained from fat con¬ taining vitamin A, green vegetables, or codliver oil, skim milk has much to commend it. Skim milk is especially useful in low-cost diets. Protein, calcium, and riboflavin are the most costly of the nutrients, and are most difficult to supply in adequate amounts when food money is scarce. Skim milk provides protein and calcium in a very cheap and use¬ ful form, and is at the same time an excellent source of riboflavin. Skim milk also has an important role in reducing diets. In these it provides many essential nutrients with low caloric value. Any deficiency in vitamin A is easily made good by butter or fortified margarine and an abundance of yellow or green vegetables, especially the green leafy ones. While skim milk has its own special role in contributing essential protein, calcium, and riboflavin to low-cost and weight-reducing diets, it should be used also in cooking and as a beverage in any diet in which the supply of whole milk is limited. [illustration: Milk Is a Favored Beverage with Growing Boys and Girls] j I » H Digestibility. Milk is a complex food and its various constituents behave differently during digestion. Because of its fluid form, milk is usually considered a liquid food. However, as soon as it reaches the stomach, the casein of milk is coagulated by the rennet there and the milk forms a semisolid jelly. There are various theories in regard to the part that the clotting of the milk plays in its digestion. The clotting separates the major portion of the protein from the other con¬ stituents which need somewhat different treatment, and prevents this casein from passing into the small intestine before it is ready for intestinal digestion. In some cases, however, the curd may become tough and cause discomfort, and may not be completely digested. In infant feeding tough curds are to be avoided. The dilution normally required in making up the formula contributes to the formation of a soft curd. Its texture is fur¬ ther improved by the use of cereal gruels, dextro maltose, and corn sirup. These car¬ bohydrates, added to supply the needed calories to the infant’s daily diet, seem also to get between the particles of casein and in¬ fluence the formation of a more tender curd. Heating milk is another method of making the curd more tender. Milk that has been boiled directly over the heat for three minutes or more, and evaporated milk which has been heated to a high temperature during canning, form tender curds that are handled much like human milk in a baby’s stomach. Milk heated in a double boiler and pas¬ teurized milk form curds somewhat softer than those of raw milk, but not so soft as the curds formed by milk heated to higher temperatures. Milk fat, because of its form, is one of the most easily digested fats. But the proportion of fat to the other constituents in milk is high and some of it may escape digestion and absorption when milk is used as an exclusive [118] food. The fat is well utilized when milk is a component of a mixed diet.