Heat-induced gelation of β-lactoglobulin/α-lactalbumin blends at pH 3 and pH 7

Mixed globular protein gels, or gel composites, based on heating solutions of proteins from milk have been investigated for many years, although the great majority of these studies have used rather crude whey isolates containing a fixed ratio of the principal components beta-lactoglobulin and alpha-lactalbumin and some denatured material. Moreover, most of the previous work has concentrated on examining structural and rheological properties of fully cured gels. In the present paper, attention is focused on well-defined mixtures composed of much purer samples of the principal components, these being present in systematically varying proportions. Protein-protein co-gels are formed at pH's 3 and 7, by heating the mixtures at 80 degrees C. Gelation is monitored by cure curve measurement and both gel times and long time limiting moduli established. A considerable difference in behavior is observed at the two pH's and modeling based on segregated phase-separated structures gives only a partial explanation of the results. It seems probable that coupled networks of some kind form in both cases. The pH 3 alpha-lactalbumin systems show a transition from reversible gelation at low temperatures to irreversible network formation above the first gel melting temperature. Conclusions from this work have generic implications for other mixed gel composite systems.