Complexation of bovine beta-lactoglobulin with 11S protein fractions of soybean (Glycine max) and sesame (Sesamum indicum).

Beta-lactoglobulin (beta-Lg) comprises 50% of the whey component of bovine milk. Protein-protein interactions between bovine beta-Lg and 11S protein fractions of soybean and sesame were investigated by turbidity, solubility behaviour and by evaluation of functional properties in the mixed systems. In this work, the aggregation behaviour of soybean and the whey protein (beta-Lg) showed the formation of soluble complexes. Turbidity and solubility studies showed that the proteins interacted at temperatures between 60 and 90+/-5 degrees C. Heating a mixture of beta-Lg and 11S proteins of soybean at higher temperatures formed soluble complexes with beta-Lg. It also reduced the self aggregation behaviour, especially that of 11S protein fraction of soybean. This reduced the precipitation of soybean proteins at higher temperature. The complex formed was resolved by gel filtration using high-performance liquid chromatography. Upon heating beta-Lg at neutral pH, native dimer starts to dissociate into monomers leading to the exposure of previously buried hydrophobic amino acids and the free thiol group. The soluble complex is formed by the exposed thiol groups. But interaction of beta-Lg with sesame 11S protein fractions did not form any soluble complexes. The mechanism of interaction indicates that hydrophobic interactions were preferred over disulfide linkages at the high salt concentrations of the buffer used. During thermal treatment the molecules are unfolded, leading to an exposure of the hydrophobic groups that further enhance the protein-protein interactions that are entropically driven hydrophobic interactions.