Effect of milk concentration on the irreversible thermal denaturation and disulfide aggregation of beta-lactoglobulin

The kinetics of beta-lactoglobulin (beta-LG) denaturation in reconstituted skim milk samples of various concentrations (9.6-38.4% total solids) over a wide temperature range (75-100 degrees C) was studied. The thermal denaturation of beta-LG had a reaction order of 1.5 at all milk solids concentrations and at all temperatures. The rate of denaturation of beta-LG was markedly dependent on the milk solids concentration and the heating temperature. At 75 degrees C, the thermal denaturation of beta-LG was retarded at higher milk solids concentrations. However, this retardation was less pronounced at higher temperatures so that a similar rate of denaturation was observed at all milk solids concentrations at 100 degrees C. From an examination of the level of disulfide-aggregated beta-LG, it was evident that most, but not all, of the denatured beta-LG was involved in disulfide-aggregated complexes, either with other denatured whey proteins or with the casein micelles. As with beta-LG denaturation, the rate of disulfide aggregation of beta-LG was markedly dependent on the milk solids concentration.