The Role of Surface-Active Constituents Involved in the Foaming of Milk and Certain Milk Products. III. Milk Lipids, including Phospholipids

Abstract

The role of milk fat in the foaming of milk, cream, buttermilk, and their artificial counterparts has been studied at temperatures between 5 and 50° C. The results suggest the following conclusions. In such emulsions two types of foam may appear separately or simultaneously, a protein type and a phospholipid-protein type. At the higher temperatures the protein type predominates. Whole milk, cream, and buttermilk exhibit minimum foaming at 30–35° C. At 35° C. the foam volume and the foam stability of skim milk are decreased as the fat content is increased up to about 5.0 per cent. With further increases in the fat content both the volume and stability of the foam increase up to a fat content of 20 per cent, after which no further increases occur. At 6° C. the foam volume remains constant regardless of the fat content. The stability of the foam reaches a minimum at about 5 per cent fat concentration, after which it increases rapidly until a fat content of 10 per cent is reached, above which cream-type foams of high stability are formed. Artificial milks and creams were made to resemble the natural product only when phospholipids (soybean) were incorporated into the fat prior to emulsification. The medium should be a protein sol; a lactalbumin sol or a milk serum protein sol such as rennet whey was satisfactory. The most normal cream was made when the medium contained natural fat globule “membrane” material; buttermilk met this condition. Emulsions of pure milk fat in skim milk, gelatin, or gum arabic sols have abnormal foaming properties. For emulsions with fat dispersed to a degree comparable to that of natural milk or cream, the optimum concentration of mixed phospholipids in the fat appears to be from 0.8 to 1.0 percent. Unbound phospholipid appears undesirable. These results have been discussed as they apply to churning, to cream whipping, to cream rebodying, and, by inference, to ice cream whipping. © 1948, American Dairy Science Association. All rights reserved.