Physical Changes in Milk Proteins at Elevated Temperatures as Determined by Light Scattering. I. Casein Fractions

The effect of elevated temperatures upon milk proteins was studied with particular attention to aggregation of purified fractions at 30, 50, 70, and 90 C. The protein fractions investigated included whole a-, fl-, a~-, and r-casein. Generally, disaggregation of the samples preceded aggregation, as indicated by variation in the turbidity of the solutions, iVfarked aggregation was observed with a~-casein at 70 C and with B-and ~-casein at 90 C. It was apparent from the magnitude of the molecular weights and radii of gyration that aggregates existed at all temperatures at pH 6.5 in 0.066 ionic strength sodium eacodylate buffer. All casein fractions except B-casein exhibited an interaction coefficient of zero whenever this quantity could be determined, and they appeared as random coils. B-Casein yielded a positive interaction coefficient and was best represented by a sphere.