Physicochemical properties of soy protein isolate–beet polysaccharide mixtures and phase inversion of their emulsion composites

This study investigated the impacts of heat treatment and mass ratio on the physicochemical and emulsion attributes of soy protein isolate (SPI) and beet polysaccharide (BSP) mixtures. In addition, the phase inversion of their emulsions in soy oil was examined. The mixtures were prepared at SPI: BSP mass ratio of 1:0, 1:1, 2:1, 5:1, and 0:1 with heated or unheated treatment. Meanwhile, their emulsions were synthesised at different oil contents of 20, 50, 100, 200, 400, 600, 800 and 1000 mL, and the microscopic morphology, appearance, conductivity, and rheology of these emulsions were assessed. Compared with the SPI - BSP mixtures produced with unheated treatment, these produced with heated treatment showed a larger particle size distribution, lower zeta-potential value, and a higher content of β-sheet structures. The synergistic effects of heat treatment and BSP addition resulted in these variations. When the amount of oil added reached 600 mL, the emulsions formed from the heated mixtures showed higher storage modulus and loss modulus. Phase inversion (i.e., from oil-in-water (O/W) to water-in-oil (W/O)) was observed in partial emulsions formed from mixtures as the oil content increased. This behaviour is governed by both the heat treatment and the SPI: BSP ratio. These results provide important theoretical insights for the design and development of novel emulsion-based systems via using SPI - BSP mixtures.