Experimental cookery

Milk from different animals varies somewhat in the proportion of the different constituents. All milk contains a high proportion of water, cow's milk averaging about 87 per cent. The milk from different breeds of cattle varies considerably in composition. The milk of individual cows of the same breed also varies in the proportion of the different constituents. This may be partly due to environment, partly to inheritance, and partly to individuality. Milk may vary particularly in fat content from one milking to the next. The percentage of fat increases during the milking period ; that is, the first milk obtained is not so rich in fat as the last portions of milk. The fat varies for different breeds from about 3.5 per cent for Holstein to about 5 per cent for Guernsey and Jersey. The protein varies from about 3.3 per cent for Holstein to 4.0 per cent for Guernsey and Jersey. It parallels the fat content somewhat, being highest in the breeds having a high fat content and lowest in those having a low fat content. The lactose does not vary so much with the different breeds as the fat and protein. The lactose content is from about 4.65 to 5 per cent. The ash varies from about 0.68 to 0.75 for the different breeds. Constituents o£ Milk Chemical and Physical Properties The constituents of milk that are most important in food preparation are enzymes, vitamins, pigments, salts, sugar, fat, and proteins. 293 294 MILK AND CHEESE Enzymes. The enzymes of cow's milk are reported as follows by Rogers; proteinases, lactase, diastase, lipase, salolase, catalase, peroxidase, and aldehydrase. Rogers states that the proteolytic enzyme, galactase, brings about slow decomposition of milk proteins into peptones, amino acids, and ammonia. Vitamins. All the vitamins recognized at the present time are contained in milk. Some are present in comparatively large and others in smaller amounts. Pigments. The appearance of milk is white. This is due to light rays reflected by the colloidally dispersed constituents of the milk, the calcium caseinate, and calcium phosphate. Milk contains two classes of yellow or orange pigments. The w^ater- soluble pigment, which imparts a yellow color with a green fluorescence to the whey of milk, was formerly called lactochrome. A name recently suggested for this pigment is lactoflavin. It is regarded as one flavin of a specific group, collectively to be called lyochromes. It is possible that lacto- flavin is composed of more than one pigment. Rogers says "lactoflavin forms compounds with saccharides, proteins, and purines (uric acid). These compounds possibly either occur naturally in milk or readily form during isolations, thus accounting for the several lactoflavins isolated from milk." It is probable that the pigment lactoflavin is one of the five fractions of vitamin G (Bo). Milk is relatively rich in this vitamin.