Thermal Stability of Whey Protein Concentrate Mixtures: Aggregate Formation

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Solutions (17% TS) of whey protein concentrate (65% protein) were dialyzed against simulated milk ultrafiltrate containing 0 to 9mM total Ca2+. The dialyzed solutions were heated at 66 or 71°C for 120min to study the effect of Ca2+ on the heat denaturation and aggregation of whey proteins. As Ca2+ decreased, the whey protein concentrate solutions formed more soluble aggregates and fewer insoluble precipitates; the amount of α-LA relative to the β-LG associated with the soluble aggregates also increased. Protein aggregates, as shown by electron microscopy of the Ca2+-adjusted solutions, became smaller and less densely packed as Ca2+ decreased. The effects of addition of low heat NDM or a mixture of Ca2+ and Na caseinate to the whey protein concentrate solution (17% TS) and heat treatment at 71°C for 120min 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 Ca2+ 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 71°C 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.