Separation of the effects of denaturation and aggregation on whey-casein protein interactions during the manufacture of a model infant formula

Abstract

Denaturation and aggregation of whey protein have been extensively studied but there is limited knowledge of their effects on processing properties of infant milk formulae (IMF) systems. In this study, the separate effects of denaturation and aggregation of whey protein on the physicochemical characteristics during processing of a model IMF were examined. Whey protein solutions (8%, w/w, protein) were pre-heated for 2 min at 72 or 85 °C, followed by addition of 2.2 mM calcium (Ca) (H-BCa), or at 85 °C after addition of the same level of Ca (H-ACa), to give pre-treated whey protein for inclusion in three model IMF systems, encoded as H-72-BCa, H-85-BCa and H-85-ACa, respectively. Unheated control samples without (UH-C) and with (UH-C-Ca) added Ca were also prepared. Model IMF systems (5.2%, w/w, protein, 60:40 whey protein:casein ratio, pH 6.8) were then prepared incorporating these pre-treated whey protein ingredients and subjected to lab-scale high-temperature short-time (HTST) heating at 85 °C for 2 min; whey protein denaturation was >81.2% in all samples after HTST. Aggregation of whey protein resulted in a significantly (P < 0.05) higher viscosity in sample H-85-ACa (8.3 mPa.s) compared to UH-C (4.0 mPa.s), and measurement of Ca ion concentration on heating showed that Ca ions enhanced whey protein aggregation, resulting in larger mean protein particle size. The results also suggest that pre-heating of whey protein had a preventative effect on aggregation of protein during HTST of IMF. This study clearly showed that aggregation is more influential than denaturation in determining viscosity development during HTST treatment of IMF, and that such viscosity development can be controlled by altering protein-protein interactions using, for example, pre-heat treatment of whey protein ingredients.