Ultracentrifugation Studies of Milk Heated to Sterilization Temperatures

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Abstract
The effect of heating milk on the sedimentation of protein particles was studied. Pictures 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: 1) Milk was preheated at 180 [plus or minus] 0.5[degree] F for 30 min., then in 2.08 sec. heated to 300 [plus or minus] 0.5[degree]F, and held for 2.08 sec., homogenized, and cooled. 2) Same as A, except milk was sterilized at 285 [plus or minus] 0.5[degree] F. 3) Milk was preheated to 180[degree] F in 2.08 sec., then heated to 300 [plus or minus] 0.5[degree] F in 2.08 sec., and held for 2.08 sec., homogenized, and cooled. 4) Same as C, except milk was sterilized at 285 [plus or minus] 0.5[degree] F. Constants for raw milk and the same milk with increasing heat treatments were, respectively, 440; 630; 844; 1355; and 2277 x 10-3. Corresponding constants for the first half of sediment were 1900; 2700; 3700; 3800; and 6600 x 10-13. After storage at 40[degree] F for 72 days, the maximum volume of sediment was approximately 10% greater; whereas, the volume of sediment from the same milks stored at 70 and 100[degree] F the same length of time was less than the initial sediment. After storage for 71 days at 100[degree] 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 milks were 1100, 1300, 2200, and 3700 x 10-13, indicating the degree of dissociation of the arger particles during storage.