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Heat-Induced Interaction between Crude -Casein and ß-Lactoglobulin¹

Departments of Dairy Technology and Chemistry, The Ohio State University, Columbus

ABSTRACT

Electrophoretic and ultracentrifuge techniques were utilized to investigate the effect of heat on systems containing crude -casein and ß-lactoglobulin. ß-Lactoglobulin complexed with -casein when mixtures of these proteins were heated in pH 6.5 and 0.02 ionic strength buffer at 65 C or higher. Electrophoretic studies revealed a 20-min heat treatment of a 1:1 mixture of these proteins resulted in 3.4% of the ß-lactoglobulin interacting with -casein at 65 C, 82.9% at 85 C, and 76.7% at 99 C. Approximately 2.2 g of ß-lactoglobulin may interact with 1.0 g of -casein if an infinite ratio of ß-lactoglobulin to casein is heated at 85 C for 20 min; whereas, only 1.4 g will interact at 99 C. Thus, the theory of independent heat denaturation of ß-lactoglobulin does not explain the results of this investigation. Ultracentrifuge studies revealed the complex to have an S₂₀ of 44–48. This compares to an S₂₀ of 3.1 for ß-lactoglobulin and 18.0 for -casein. The phosphorus content of the casein in the complex averaged 0.20%. This corresponds to the reported phosphorus value of -casein.

¹ Article No. 861, Department of Dairy Technology, The Ohio State University, Columbus. Aided by a research grant from the Council on Research, The Ohio State University.

² Currently with the Nopco Chemical Co., Newark, New Jersey.