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

Lawrence K. Creamer, Fonterra Research Centre
Annie Bienvenue, California Polytechnic State University - San Luis Obispo
Hanna Nilsson, Lund University
Marie Paulsson, Lund University
Miriam van Wanroij, Wageningen Agricultural University
Edwin K. Lowe, Fonterra Research Centre
Skelte G. Anema, Fonterra Research Centre
Michael J. Boland, Fonterra Research Centre
Rafael Jiménez-Flores, California Polytechnic State University - San Luis Obispo

Abstract

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.