Experimental cookery

The adsorbed films surrounding the fat globules may also be destroyed by the addition of acid or alkali. It is by these methods that the fat is set free for a quantitative determination. In the Babcock.test, acid is used for liberating the fat globules ; in the Hoyberg test alkali is used. The Bab- cock, or some modification of it, is the one usually employed in estimating the fat content of milk and cream. Protein. The chief proteins found in milk in order of their decreasing amounts are casein, lactalbumin, and lactoglobulin. Casein. Casein belongs to the group of phosphoproteins. The form in which the phosphorus exists in the casein is not definitely known, but it is believed to be present in the form of combined phosphoric acid. Casein forms about 3 per cent of cow's milk. At its isoelectric point, which is pH 4.6, casein is nearly insoluble in water. Casein is amphoteric and forms salts with acids and alkalies. Fresh milk has a reaction of about pH 6.6, so that the casein is present in the milk as salts of bases and is found as calcium and magnesium caseinates. All the alkali caseinates are soluble in water, though the salts of the alkaline earths are less soluble than the alkali ones. Loeb states that below 298 MILK AND CHEESE />H 4.6 the casein chloride, casein acetate, and casein lactate are very soluble in water, but casein sulfate and casein oxalate are difficultly soluble. According to Zoller, pure casein when heated in water begins to imbibe water at 80° to 90 °C. and becomes plastic. In this form it can be molded and shaped. Upon cooling it becomes very hard. Casein can be precipitated from milk by bringing the milk to the isoelec- tric point of casein. Coagulation of casein will be considered later. Lactalbumi?!. The proportion of lactalbumin in milk is much lower than that of casein. It forms about 0.50 per cent of cow's milk. Its isoelectric point is /)H 4.55. Since the reaction of fresh milk is about /)H 6.6, it is on the alkaline side of the isoelectric point of lactalbumin. Thus is it possible that the lactalbumin is found combined as salts of bases, such as calcium and magnesium albuminates. Osborne and Wakeman think it is uncom- bined. Lactalbumin is soluble in water, and is coagulated by heating in solution to a temperature of about 70°C. Coagulation may not be complete at this temperature. Palmer states that the lactalbumin is more highly dis- persed than the other colloidal constituents of the milk. LactoglohuUn. Lactoglobulin occurs in milk in very small quantities, about 0.05 per cent of cow's milk. Lactoglobulin is insoluble in distilled water, but it is soluble in dilute solutions of strong bases or acids, and in dilute salt solutions. It is coagulable by heat. Homogenization of Milk