Effect of different types and concentrations of fat on the physico-chemical properties of soy protein isolate gel

The effect of different types of fat (anhydrous milk fat, palm stearin, soybean oil) and concentrations (0.5, 1, and 2%) in soy protein isolate (SPI) gel on their gelation behaviour (acidification, cooling, annealing and heating step), tribological, microstructure and textural properties were investigated. SPI gels made from soy protein isolate added with different fat types showed different gelation behaviour compared to control (without fat) by modulating the acidification time. Among all the gels, incorporating anhydrous milk fat into soy protein produced stronger and firmer gels (0.66–0.73 N) followed by palm stearin (0.64–0.68 N) and soybean oil (0.60–0.62 N). The apparent viscosity for all samples showed a shear thinning behaviour. The lowest coefficient of friction were observed from SPI gels added with 2% of anhydrous milk fat which indicating better lubrication properties. The gel particle sizes of all the samples were also not significantly different, although from microscopic images the soy protein with soybean oil showed smaller fat globules and more compact protein network. These results demonstrated that the presence of fats as a filler affects the firmness and gelling properties of SPI gel. The highest G′ (~1.4 kPa) and the lowest friction coefficient (0.24) of SPI gel obtained from 2% of anhydrous milk fat addition suggested the potential of incorporating anhydrous milk fat to provide desirable texture and pleasant mouthfeel in SPI gel.