Heat-induced gelation of beta-lactoglobulin/alpha-lactalbumin blends at pH3 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 g reat majority of these studies have used rather crude whey isolates contain ing a fixed ratio of the principal components beta-lactoglobulin and alpha- lactalbumin and some denatured material. Moreover, most of the previous wor k has concentrated on examining structural and rheological properties of fu lly 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-gel s are formed at pH's 3 and 7, by heating the mixtures at 80 degrees C. Gela tion is monitored by cure curve measurement and both gel times and long tim e limiting moduli established. A considerable difference in behavior is obs erved at the two pH's and modeling based on segregated phase-separated stru ctures gives only a partial explanation of the results. It seems probable t hat coupled networks of some kind form in both cases. The pH 3 alpha-lactal bumin systems show a transition from reversible gelation at low temperature s to irreversible network formation above the first gel melting temperature . Conclusions from this work have generic implications for other mixed gel composite systems.