Disulfide Bond Formation Between Thermally Denatured ß-Lactoglobulin and -Casein in Casein Micelles

¹ Department of Food Science, Southeast Dairy Foods Research Center, North Carolina State University, Raleigh 27695-7624

Interaction between thermally denatured ß-lactoglobulin and -casein has been suggested to occur via a sulfhydryl-disulfide interchange leading to an intermolecular disulfide bond. Direct evidence for a sulfhydryl-disulfide interchange between ß-lactoglobulin and -casein in native casein micelles was obtained by heat treatment of native micelles, obtained and used immediately without exposure to temperature below 20°C, in the presence of ß-lactoglobulin that was covalently immobilized on 3000-Å pore diameter porous glass beads. Washing the beads with low pH urea solutions removed all non-covalently bound proteins without further interchange. Treatment of the washed beads with a reducing agent released protein attached through disulfide bonds which was then identified by PAGE. Only -casein could be identified in the reductively released protein. No reductively released protein could be detected in samples treated at 55 or 65°C. A small amount of -casein was present in the reductive eluant following heat treatment at 75°C; however, a much greater amount was attached through intermolecular disulfide bonds when the mixture was heated at 85°C.

Key Words: disulfide bond formation • casein micelles • thermal denaturation

Submitted on August 7, 1989
Accepted on October 19, 1989

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