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Physical and Chemical Properties of the Fat Globule Adsorption "Membrane." II. Nature and Origin of Surface Active Materials Involved in Curd Tension Reduction and Prevention of Rennet Clot of Cow's Milk by "membranes" from Natural and Synthetic Creams^*

Division of Agricultural Biochemistry, University of Minnesota, St. Paul, Minn.

N. P. Tarassuk

Division of Dairy Industry, University of California, Davis, Calif.

ABSTRACT

Experiments are described showing a reduction in curd tension when artificial fat globule "membrane" sols derived from spray dried whey were added directly to natural or "remade" skim milk. Since some of these sols exhibited evidence of protein denaturation on shaking, the experiments suggest that this may interfere, under some conditions, with normal clotting of milk by rennet.

Experiments are described showing that the normal rennet clot may be completely prevented by emulsifying a small amount of diglycol laurate into raw milk at room temperature, aging the emulsion in the cold and adding rennet at 35° C. This phenomenon also occurs in "remade" buttermilks from "creams" whose butter fat globule "membrane" is diglycol laurate. A decrease in surface tension and pH accompanies the destruction of clotting ability. The explanation of this phenomenon is the liberation of lauric acid from the diglycol ester by natural milk enzyme. It does not occur if the milk is first pasteurized.

^* Paper No. 1777, Scientific Journal Series, Minnesota Agricultural Experiment Station.