Physico-chemical changes in heat treated micellar casein - Soy protein mixtures

- Micellar casein - soy protein mixtures heat treated at 95 °C for 15 min form gels.
- No chemical bonds between soy proteins and casein micelles form below 95 °C.
- Micellar casein - soy protein mixtures can be used to develop high protein foods.

This study presents a rheological and chemical evaluation of the changes induced by heating of micellar casein (MCN) - soy proteins (SP) mixtures. Individual and mixed (1:1) protein preparations of 10 g/100 g and 15 g/100 g concentration were prepared and heat treated for 15 min at 40 °C, 60 °C and 95 °C, respectively. After cooling to 20 °C, their steady-shear and dynamic rheological properties were determined. Apparent viscosity of MCN, SP and their mixtures increased with concentration. Most heat treated MCN-SP mixtures had liquid-like behavior, except the 15 g/100 g mixture, which formed a gel after treatment at 95 °C. A differential solubility method was used to investigate the degree of protein denaturation, and non-reducing SDS-PAGE analysis to identify specific protein fractions in the heat treated protein systems. Heat treatments did not induce any chemical interactions between soy proteins and casein micelles in the mixed MCN-SP systems, but the 95 °C treatments induced denaturation and subsequent interactions among soy proteins when the critical concentration for gelation was exceeded. Nonetheless, mixtures with interesting rheological properties were obtained, which could be used in the development of high protein foods with unique textural and mouthfeel characteristics.