Thermal Stability of Whey Protein Concentrate Mixtures: Aggregate Formation

Solutions (17% TS) of whey protein concentrate (65% protein) were dialyzed against simulated milk ultrafiltrate containing 0 to 9 mM total Ca 2+ . The dialyzed solutions were heated at 66 or 71C for 120 min to study the effect of Ca 2+ on the heat denaturation and aggregation of whey proteins. As Ca 2+ decreased, the whey protein concentrate solutions formed more soluble aggregates and fewer insoluble precipitates; the amount of a-LA relative to the b-LG associated with the soluble aggregates also increased. Protein aggregates, as shown by electron microscopy of the Ca 2+ -adjusted solutions, became smaller and less densely packed as Ca 2+ decreased. The effects of addition of low heat NDM or a mixture of Ca 2+ and Na caseinate to the whey protein concentrate solution (17% TS) and heat treatment at 71C for 120 min on whey protein denaturation and aggregate formation were also investigated. Compared with the whey protein concentrate solution (17% TS), whey protein denaturation was much lower when low heat NDM was added to the solution, but not when a mixture of Ca 2+ and Na caseinate was added. Electron micrographs showed that the whey protein aggregates that formed upon heating the mixture of whey protein concentrate and low heat NDM at 71C were smaller and less dense, and the micellar appendages were more compact, than those in the whey protein (17% TS) or low heat NDM (27% TS) solutions. The micrographs of the mixture of whey protein concentrate and caseinate were not comparable with either that of low heat NDM or of the mixture of whey protein concentrate and NDM. ( Key words: calcium, casein,