Microstructural properties of heat-set whey protein gels: Effect of pH

In this study, the microstructure of gels made from beta-lactoglobulin (bet a-lg), alpha-lactalbumin (alpha-lac), bovine serum albumin (BSA) and mixtur es of these proteins prepared ar pH 3 an 8.6 were studied by transmission e lectron microscopy. The results shows that at pH 3, beta-lg, alpha-lac and alpha lac/beta-lg gels/aggregates consisted of dense compact particulate gl obules with diameter ranging from 1 to 4 mu m while BSA, BSA/alpha-lac and BSA/beta-lg gels were filamentous and fluffy in nature with globule diamete rs in the nanometer scale. The sizes of the globules formed by alpha-lac we re up to four times larger than those formed by beta-lg/BSA and alpha-lac/B SA mixtures formed gels with interpenetrating networks at pH 3. At pH 8.6, the BSA, BSA/alpha-lac and BSA/beta-lg micrographs showed gel networks made up of very finestranded random aggregates; gels formed by alpha-lac, beta- lg and alpha-lac/beta-lg consisted of much larger aggregates. The micrograp hs of the alpha-lac and beta-lg/alpha-lac gels formed at alkaline pH showed them to consist of a phase-separated network. Visual observation showed al l the gels formed at pH 3 to be opaque while those at pH 8.6 were transluce nt.