Interactions between K-Casein and ß-Lactoglobulin: Effects of Anions on Covalent Stabilization of the Complex

Structure breaking anions, trichloroacetate (—TCA _-) and thiocyanate (—SCN_-), significantly increased the interaction between k-casein (K-C) and ß-lactoglobulin (B-Lg) to give the covalently stabilized K-C/B-Lg tetrameric (A4) complex, whereas “structure making” anions, chloride (—Cl_-) and especially sulfate (— SO _4-), reduced it. The reactivity of K-C with B-Lg in the presence of these anions followed the order, —TCA_- > — SCN _- > — Cl _- > — SO_4- (100 mM). The percentile distribution of the covalent bonded K-C/B-Lg A4 complex after 720 s of heating at 70°C in —TCA_- (100mM) was one order greater than it was in — SO_4- - During storage of the heated K-C/B-Lg mixture, the B-Lg A3/K-C interaction in —TCA_- was rapid and uneffected by the holding temperature, whereas in —SO_4-, the reaction rate was inversely related to the temperature, being apparently controlled by the relative concentration of monomeric K-C.