K-CASEIN HETEROGENEITY AND MILD HEATING EFFECTS ON SUSCEPTIBILITY TO CHYMOSIN ACTION

Bovine SH-kappa-casein (kappa-C-pool) was fractionated into five components based on carbohydrate and sialic acid contents (kappa-C-P1 < kappa-C-P2 < kappa-C-P3 < kappa-C-P4 < kappa-C-P5) by ion-exchange chromatography (DEAE-cellulose). Chymosin susceptibility observed by monitoring changes in optical density during enzyme action, varied among the components. This was a reflection of the difference in self-association of the proteins in aqueous dispersion as determined by hydrophobic interaction chromatograph. There was an inverse relationship between surface hydrophobicity of the protein polymers (kappa-C-P2 > kappa-C-P3 > kappa-C-P4 > kappa-C-P5 > kappa-C-P1 > kappa-C-pool) and their susceptibility to chymosin at 37-degrees-C, pH 6.8 (kappa-C-pool > kappa-C-P1 > kappa-C-P5 > kappa-C-P4 > kappa-C-P3 > kappa-C-P2). Mild heating decreased susceptibility and affected flocculation of all except the highly glycosilated components kappa-C-P4 and kappa-C-P5 reflecting amphipathicity imparted thermostability.