Heat-Induced Redistribution of Disulfide Bonds in Milk Proteins. 1. Bovine β-Lactoglobulin

Changes in the structure and chemistry of β-lactoglobulin (β-LG) play an important role in the processing and functionality of milk products. In model β-LG systems, there is evidence that the aggregates of heated β-LG are held together by a mixture of intermolecular non-covalent association and heat-induced non-native disulfide bonds. Although a number of non-native disulfide bonds have been identified, little is known about the initial inter- and intramolecular disulfide bond rearrangements that occur as a result of heating. These interchange reactions were explored by examining the products of heat treatment to determine the novel disulfide bonds that form in the heated β-LG aggregates. The native protein and heat-induced aggregates were hydrolyzed by trypsin, and the resulting peptides, before and after reduction with dithiothreitol, were separated by high-performance liquid chromatography and their identities confirmed by electrospray ionization mass spectrometry. Comparisons of these peptide patterns showed that some of the Cys160 was in the reduced form in heated β-LG aggregates, indicating that the Cys160−Cys66 disulfide bond had been broken during heating. This finding suggests that disulfide bond interchange reactions between β-LG non-native monomers, or polymers, and other proteins could occur largely via Cys160. Keywords: β-Lactoglobulin; disulfide bonding; heat-induced change; mass spectroscopy