Microstructural Properties of Heat-set Whey Protein Gels: Effect of pH

In this study, the microstructure of gels made from -lactoglobulin ( -lg), -lactalbumin ( -lac), bovine serum albumin (BSA) and mixtures of these proteins prepared at pH 3 and 8.6 were studied by transmission electron microscopy. The results showed that at pH 3, -lg, -lac and -lac/ lg gels/aggregates consisted of dense compact particulate globules with diameters ranging from 1 to 4 µ m while BSA, BSA/ -lac and BSA/ -lg gels were filamentous and fluffy in nature with globule diameters in the nanometer scale. The sizes of the globules formed by -lac were up to four times larger than those formed by -lg. The -lg/BSA and -lac/BSA mixtures formed gels with interpenetrating networks at pH 3. At pH 8.6, the BSA, BSA/ -lac and BSA/ -lg micrographs showed gel networks made up of very finestranded random aggregates; gels formed by -lac, -lg and -lac/ -lg consisted of much larger aggregates. The micrographs of the -lac and -lg/ -lac gels formed at alkaline pH showed them to consist of a phase-separated network. Visual observation showed all the gels formed at pH 3 to be opaque while those formed at pH 8.6 were translucent.