Thermal modification of functional properties of proteins from acid whey

Acid whey was prepared from reconstituted low heat skimmed milk powder fermented with Lactobacillus helveticus. After separation of casein curd at pH 4.7, the acid whey was adjusted to pH 3.25 and different batches were thermally modified at 90°C for 2.5-15min. These were further centrifuged and ultrafiltered to a volume reduction ratio of 10. The proteins in the acid whey protein concentrate (WPC) consisted of about 69% β-lactoglobulin (β-Lg), 22% α-lactalbumin and 9% immunoglobulin and no serumalbumin was detectable. The protein unfolding of β-log followed an apparent reaction order n=1.5 and it was shown that the predenaturation had significant influences on the filterability as well as on the functionality of acid WPC's. Flux of ultrafiltration decreased with increasing intensity of heating. Best surface properties were obtained after a thermal modification at pH 3.25 and 90°C for 2.5 min with about 10% degree of denaturation of β-log. The foaming and emulsifying properties of both the acid WPC and especially of modified acid WPC exceeded those of commercial WPC from sweet whey clearly. Conversely, the gel forming properties were not enhanced by the thermal modification although gels were formed at lower temperatures with increasing degree of predenaturation of β-Lg.