Thermal denaturation of bovine immunoglobulin G and its association with other whey proteins

Abstract

Thermal denaturation of bovine immunoglobulin G (IgG) was studied alone and in the presence of major whey proteins. The two heating regimes studied provided the simulated thermal effect compared to high-temperature short-time (HTST, 72 °C/15s) and ultra-high temperature (UHT, 100 °C/30s equivalent to 140°C/5s in terms of denaturation of β-lactoglobulin) conditions. Simulated HTST conditions least impacted on the secondary structure of IgG and other whey proteins when they were present either alone or in mixtures of whey proteins. The heating at 100 °C for 30s caused formation of covalent-complexes of IgG alone, as well as in the mixtures, mainly through thiol-disulfide reactions. Under 100 °C/30s treatment, bovine serum albumin (BSA) did not interact with IgG through thiol-disulfide reactions in a binary mixture of proteins (IgG and BSA). α-Lactalbumin (ALA) appeared to preferentially lead denaturation of whey proteins over β-lactoglobulin (BLG), in a protein mixture (BLG, ALA, IgG, and BSA), suggesting a possible catalytic role by BSA and/or IgG on ALA, while native whey contains another component that can inhibit this effect. The presence of other whey proteins did not contribute to thermal stability of IgG at 100 °C.