SEASONAL-CHANGES IN THE PHYSICAL AND FUNCTIONAL-PROPERTIES OF WHEY-PROTEIN CONCENTRATES

Seasonal variations have been monitored in the milk supply and in six physical and functional properties of commercial whey protein concentrate (75% protein) manufactured at intervals over a single lactation cycle in southeastern Australia. Recently, we reported that percentages of the major proteins in whey protein concentrate varied inversely; late season powders were characterized by a high proportion of beta-lactoglobulin and a low proportion of alpha-lactalbumin. In the present study, transition energy associated with protein denaturation was reduced for whey protein concentrate prepared in the final 3 mo of lactation. This decrease paralleled a similar decrease in alpha-lactalbumin content and surface hydrophobicity of the whey protein concentrate. Other seasonal changes in the functional properties of whey protein concentrate included increased foaming capacity and decreased foam stability for whey protein concentrate prepared in the latter half of lactation. Heat-induced gel firmness was generally higher for whey protein concentrate manufactured in the final 3 mo of the lactation cycle, an observation that paralleled an increased proportion of beta-lactoglobulin in whey protein concentrate prepared at that time.