Stability of emulsion stabilized by low-concentration soybean protein isolate: Effects of insoluble soybean fiber

Effects of insoluble soybean fiber (ISF) on the emulsion properties stabilized by soybean protein isolate (SPI, 0.40 wt%) and the stability of emulsions exposed to environmental conditions (pH and NaCl) were studied in this paper. As ISF increased (0-0.40 wt%), higher zeta-potential and smaller d(4,3) of suspended SPI/ISF complexes were observed in aqueous system, which might be due to the interactions between SPI and ISF and the formation of SPI/ISF complexes. The zeta- potential of emulsions continuously decreased, the d(4,3) firstly decreased and then increased while surface protein content (P-A) and concentrations (Gamma), viscosity as well as storage modulus (G') continuously increased, which might be related to the low concentration of SPI, the SPI/ISF interactions and excessive unadsorbed ISF molecules in the continuous phase. The emulsions exhibited better resistance to pH and salt with increasing ISF while ISF also had a positive effect on the storage stability. All the results indicated that ISF could promote the stability of SPI emulsion, which was most likely ascribed to the electrostatic interactions, the gel-like network structure and the function of ISF as emulsifier and thickener, facilitating adsorption of protein onto the oil droplet surface and enhancing the interfacial protective coating. In summary, the ISF has a great potential to be applied in the emulsion system containing low-concentration protein, thus lowering the addition of protein and endowing the nutritional value of insoluble dietary fiber.