GELATION OF BOVINE SERUM-ALBUMIN AND BETA-LACTOGLOBULIN - EFFECTS OF PH, SALTS AND THIOL REAGENTS

The formation of heat-induced gels from bovine serum albumin (BSA) and beta-lactoglobulin (beta-Lg) under different conditions was studied. The minimum protein concentration required for formation of self-supporting gels in 100 mM Tris-HCl buffer (pH 8.0) following heating at 90-degrees-C for 15 min was 4% for BSA and 5% for beta-Lg. Maximum gel hardness for both BSA and beta-Lg occurred at pH 6.5. The hardness of beta-Lg gels reached a maximum with the addition of 20-40 mM NaCl or 2 mM CaCl2, while BSA was at a maximum with 5 mM CaCl2 but were unaffected by NaCl. The hardness of beta-Lg gels decreased slightly upon addition of various anions of sodium (between 50 and 100 mM). The effects followed the lyotropic series. Addition of N-ethylmaleimide (NEM) decreased gel strength of BSA, while the gel hardness of beta-Lg increased slightly with 5 mM NEM but decreased at higher NEM levels. Dithiothreitol (DTT), at 5 and 2 mM, respectively, enhanced gel hardness of BSA and beta-Lg gels. Higher DTT levels significantly decreased gel hardness for both BSA and beta-Lg. These results indicated that disulfide bonds are important in BSA gels, while electrostatic interactions and disulfide bonds are involved in the formation and maintenance of beta-Lg gels.