THERMAL-STABILITY OF WHEY-PROTEIN CONCENTRATE MIXTURES - AGGREGATE FORMATION

Solutions (17% TS) of whey protein concentrate (65% protein) were dial yzed against simulated milk ultrafiltrate containing 0 to 9 mM total C a2+. The dialyzed solutions were heated at 66 or 71 degrees C for 120 min to study the effect of Ca2+ on the heat denaturation and aggregati on of whey proteins. As Ca2+ decreased, the whey protein concentrate s olutions formed more soluble aggregates and fewer insoluble precipitat es; the amount of alpha-LA relative to the beta-LG associated with the soluble aggregates also increased. Protein aggregates, as shown by el ectron microscopy of the Ca2+-adjusted solutions, became smaller and l ess densely packed as Ca2+ decreased. The effects of addition of low h eat NDM or a mixture of Ca2+ and Na caseinate to the whey protein conc entrate solution (17% TS) and heat treatment at 71 degrees C for 120 m in on whey protein denaturation and aggregate formation were also inve stigated. 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 th at formed upon heating the mixture of whey protein concentrate and low heat NDM at 71 degrees C were smaller and less dense, and the micella r appendages were more compact, than those in the whey protein (17% TS ) or low heat NDM (27% TS) solutions. The micrographs of the mixture o f whey protein concentrate and caseinate were not comparable with eith er that of low heat NDM or of the mixture of whey protein concentrate and NDM.