Heat-Induced Interaction between Crude κ-Casein and β-Lactoglobulin

Eleetrophoretic and ultracentrifuge teehniques were utilized to investigate the effect of heat on systems containing crude K-casein and fl-lactoglobulin. B-Laetoglobulin complexed with K-casein when mixtures of these proteflls were heated in pH 6.5 and 0.02 ionic strength buffer at 65 C or higher. E'lectrophoretic studies revealed a 20-rain heat treatment of a 1:1 mixture of these proteins resulted in 3.4% of the B-lactoglobulin interacting with K-casein at 65 C, 82.9% at 85 C, and 76.7% at 99 C. Approximately 2.2 g of fl-laetoglohulin may interact with 1.0 g of ,~-casein if an infinite ratio of B-lactoglobulin to casein is heated at 85 C for 20 rain; whereas, only 1.4 g will interact at 99 C. Thus, the theory of independent heat denaturation of /3-1aet~globulin does not explain the results of this investigation. Ultracentrifuge studies revealed the complex to have an S:~ of 44-48. This compares to an S~, of 3.1 for /3-1actoglobulin and 18.0 for K-casein. The phosphorus content of the casein in the complex averaged 0.20%. This corresponds to the reported phosphorus value of K-casein.