Partial replacement of milk proteins with plant proteins is a challenge due to the reported negative effect on physical and sensory properties. Understanding of how the mechanical properties of acidified milk gels can be restored when 30% casein is replaced with soy proteins is therefore explored. Mixtures of sodium caseinate (CAS) and soy proteins (SP) are pre-heated at different conditions (pH, ratio CAS:SP, temperature) prior to acidification with GDL in order to modulate aggregation, structure build-up and final mechanical properties of acidified gels with total protein content of 10% (w/w). Optimal results in mechanical response were obtained when CAS and SP were pre-heated together at a 7:3 protein ratio for 15 min at 95 °C. In addition, heat treatment of CAS-SP mixtures resulted in a shift to higher onset pH and a faster onset gelation as determined by dynamic oscillation rheology. From turbidity measurements a change in aggregation kinetics was observed which can be appointed to the altered aggregation propensity during acidification of the heat induced aggregates. Pre-heating of CAS and SP together resulted in an enhanced increase in aggregate size (as determined with light scattering) compared to unheated mixture or when only SP was heated. By pre-heating mixtures of CAS and SP at the right conditions prior to acidification, the mechanical response of mixed CAS-SP gels can be restored to that comparable with CAS only gels. As a result, 30% CAS can be successfully replaced with SP while maintaining mechanical properties.
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