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

b-Lactoglobulin (b-Lg) comprises 50% of the whey component of bovine milk. Protein�protein
interactions between bovine b-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 (b-Lg)
showed the formation of soluble complexes. Turbidity and solubility studies showed that the
proteins interacted at temperatures between 60 and 90958C. Heating a mixture of b-Lg and
11S proteins of soybean at higher temperatures formed soluble complexes with b-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 b-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 b-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.