Gelation of bovine serum albumin and β-lactoglobulin; effects of pH, salts and thiol reagents

Abstract

The formation of heat-induced gels from bovine serum albumin (BSA) and β-lactoglobulin (β-Lg) under different conditions was studied. The minimum protein concentration required for formation of self-supporting gels in 100 m m Tris-HCl buffer (pH 8·0) following heating at 90°C for 15 min was 4% for BSA and 5% for β-Lg. Maximum gel hardness for both BSA and β-Lg occurred at pH 65. The hardness of β-Lg gels reached a maximum with the addition of 20–40 m m NaCl or 2 m m CaCl 2, while BSA was at a maximum with 5 m m CaCl 2 but were unaffected by NaCl. The hardness of β-Lg gels decreased slightly upon addition of various anions of sodium (between 50 and 100 m m). The effects followed the lyotropic series. Addition of N-ethyl-maleimide (NEM) decreased gel strength of BSA, while the gel hardness of β-Lg increased slightly with 5 m m NEM but decreased at higher NEM levels. Dithiothreitol (DTT), at 5 and 2 m m, respectively, enhanced gel hardness of BSA and β-Lg gels. Higher DTT levels significantly decreased gel hardness for both BSA and β-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 β-Lg gels.