Ultracentrifugation Studies of Milk Heated to Sterilization Temperatures

The effect of heating milk on the sedimentation of protein particles was studied. P[etm'es taken of sediment during ultracentrifugation were measured to determine sedimentation constants in Svedberg units which were calculated for the last measured fractions of sediment thrown from solution at 10,000 G. Heating was done as follows : A. Milk was preheated at 180 0.5 F. for 30 rain., then in 2.08 sec. heated to 300 0.5 F., and held for 2.08 see., homogenized, and cooled. B. Same as A, except milk was sterilized at 285 0.5 F. C. Milk was preheated to 180 ]~. in 2.08 see., then heated to 300 0.5 F. in 2.08 see., and held for 2.08 sec., homogenized, and cooled. D. Same as C, except milk was sterilized at 285 -----0.5 F. Constants for raw milk and the santo milk with increasing heat treatments were, respectively, 440; 630; 846; 1,355; and 2,277 10 -1~. Corresponding constants for the first half of sediment were 1,900; 2,700; 3,700; 3,800; and 6,600 X 10 -~. After storage at 40 F. for 72 days, the nmximum volume of sediment was approximately 10% greater; whereas, the volume of sediment from the same milks stored at 70 and 100 F. the same length of time was less than the initial sediment. After storage for 71 days at 100 F., sedimentation constants for volumes of sediment equal to the respective volumes upon which constants for the first half of the sediment were calculated in freshly processed nfilks were 1,100, 1,300, 2,200, and 3,700 10 -~, indicating the degree of dissociation of the larger particles during storage.