Heat-induced gelation of aqueous micellar casein suspensions as affected by globular protein addition

Abstract : The aim of this work was to investigate how the heat-induced gelation of micellar casein (MC) suspensions (6% w/w MC) is affected by the addition of three globular proteins (GP) (whey proteins (WP), pea proteins (PP) and soy proteins (SP); from 0 to 6% w/w) at pH ≤ 6.0. Storage moduli (G′) were measured as a function of temperature from 20 °C to 90 °C. Heat-induced gelation was characterised by a sharp increase in G′ at a critical temperature (Tc). The suspensions were then held at 90 °C for 1h to determine the stiffness of the gels. Regardless of the pH, Tc of MC suspensions increased with the addition of GP. Interestingly, this increase depended on the type of GP and was stronger in the order SP > PP > WP. This effect was mainly explained by differences in calcium binding efficiency between the different GP (SP > PP >> WP) and/or the mineral composition of the ingredients. Native GP influence gelation of MC by binding calcium, thus reducing the amount available for MC to bridge, leading to an increase in Tc. Tc of the suspensions decreased with decreasing pH due to both decrease in the net charge density of MC and release of Ca2+ that in turn favoured heat-induced gelation of MC. Gel stiffness was not influenced much by PP or SP addition. However, it increased significantly in the presence of WP, due to co-aggregation of denatured WP with MC above 70 °C, which reinforced the MC network.