Stabilization of oil-in-water emulsion gels by pH-induced electrostatic interactions between soybean protein isolate microgel particles and xanthan gum

In this paper, a colloidal dispersion at different pH containing soybean protein isolate (SPI) microgel particles and xanthan gum (XG) was used as the aqueous phase to prepare O/W emulsion gels with soybean oil. Properties of SPI microgel particles were analyzed by particle size, Zeta-potential, secondary structure, optical contact angle, dynamic interface tension, and SEM testing, respectively. Results showed that pH impact microgels particle size and Zeta-potential and their emulsification properties. It turned out that only at pH 3, 6, 7, and 8 can construct emulsions successfully. Based on a comparison of microstructure and macroscopic properties, it was found that at pH 3, proteins and polysaccharides were oppositely charged, electrostatic attraction between them reduced proteins located at the interface, and was more likely to form larger droplets, resulting in a bimodal droplet distribution and larger sizes. Conversely, at the pH of 6, 7, and 8, respectively, emulsions exhibited a uniform droplet distribution and more solid-like rheological properties due to the powerful electrostatic repulsion between SPI and XG. Also, emulsion gels co-stabilized with proteins and polysaccharides under electrostatic repulsion conditions showed an ideal recovery ability. Overall, this work would be beneficial to the use of emulsion gels in fat substitute systems.