Effects of the addition sequence of soybean protein isolate and cellulose nanofibers on the properties and in vitro digestion of emulsions

In this study, soybean protein isolate (SPI) and cellulose nanofibers (CNF) were used to prepare an oil-in-water emulsion. The effect of the sequence of adding SPI and CNF on the properties of the emulsion was examined by analyzing the emulsion index, microstructure, droplet size, zeta potential, rheological behavior, and in vitro gastrointestinal digestion characteristics of the emulsion. By using both SPI and CNF as emulsifiers, a better emulsification effect was obtained than using SPI or CNF alone. The particle size of the emulsion with SPI added first and CNF added later was smaller than that of the emulsion with CNF added first and SPI added later. And the emulsions with SPI added first had more cellulose nanofibers in the aqueous phase system. The emulsion with CNF added first and SPI added later was more likely to form a three-dimensional network structure; thus, it is more conducive to reducing the release of free fatty acids. When 50 mmol/L NaCl was added to the emulsion, the emulsion droplets gathered, and the viscosity increased, which was conducive to the formation of three-dimensional network gel structure of emulsion, but at the same time, the ability to release free fatty acids was improved.