Heat-induced gelation of micellar casein/plant protein oil-in-water emulsions

Abstract

The heat-induced gelation of oil-in-water emulsions stabilised by mixtures of micellar caseins (MC) and plant proteins (PLP) was investigated in order to assess the potential of PLP to replace milk proteins for the development of novel food products. The aim of this work was to investigate how the heat-induced gelation of MC/PLP oil-in-water emulsions is affected by sunflower oil content (0, 5, 10 and 15% w/w) and total protein content in the aqueous phase (C; from 1 to 4% w/w) at different protein compositions (MC/PLP = 100/0 to 0/100) and pH 5.8. Two types of PLP were used: soy proteins (SP) and pea proteins (PP). Storage moduli (G') were measured during heating ramps from 20 to 90 °C and heat-induced gelation was characterised by an increase in G' at a gelation temperature (Tg). The gel stiffness (Gel) was determined after 1 h at 90 °C and the microstructure of the emulsion gels was observed by confocal laser scanning microscopy (CLSM). Tg increased when an increasing fraction of MC was replaced by SP or PP, due to binding of calcium to PLP. Tg decreased with increasing oil content in the MC/PLP emulsions mainly up to 10% w/w oil, explained by protein interactions at the oil-water interface. Generally, MC could be successfully replaced by PLP while maintaining the same Gel. Gel increased with increasing oil content, suggesting that oil droplets acted as active fillers in the emulsion gels, which was confirmed by CLSM images. Gel slightly increased with increasing C from 1 to 4% w/w. It was also shown that PLP can be used instead of whey proteins in MC/whey protein oil-in-water emulsions while maintaining the same Gel.