The changes and gastric digestive properties of gel were investigated for oxidized myofibrillar protein (MP) (0–1 mmol/L H₂O₂) treated by 30% substitution of NaCl with KCl, MgCl₂, and KCl/MgCl₂. Mild oxidation level (0.3 mmol/L H₂O₂) facilitated the protein unfolding, and MgCl₂ obviously intervened the protein self-assembly by forming the salt bridge and more disulfide bonds. At the same oxidation concentration, the sodium-reduced MP substituted with KCl formed dense network structure with better gel strength (increased by 6%–18%) and water retention in comparision to the gel without sodium reduction. The KCl-substituted gel chewing work was also relatively higher among the low-sodium samples at the first chewing cycle. Reversely, the relatively soft structure and lower gel viscosity in simulated oral chewing were found in MgCl₂-substituted gel. These changes decreased the contact limit between pepsin and protein for better gastric disintegration or pepsin diffusivity, and increased the proportion of small molecular weight peptides (25.83%, < 5 kDa). Therefore, partial substitution of NaCl with other salt replacers could influence the physicochemical properties of low-sodium MP suspension or gel under different oxidation degree and the subsequent gastric digestion characteristics.

The soy protein isolate was modified by adding different concentrations of tea polyphenols extract to prepare the oil-in-water (O/W) emulsion. The interfacial tension, interfacial protein adsorption fraction, emulsion particle size and zeta potential were investigated to explore the effect of tea polyphenols on the properties of soy protein isolate emulsion and interfacial protein displacement. The results show that the interfacial tension of soy protein isolate is increased after the addition of tea polyphenols. When soy protein isolate (1%, mass concentration) and soy oil are prepared into O/W emulsion with 9:1 mass ratio by high-speed shear and ultrasound, tea polyphenols addition can improve the emulsion stability. Compared to the blank control group, when the amount of tea polyphenols added is 0.04%, the particle size of emulsion decreases significantly from 1.702 μm to 1.203 μm (P < 0.05), the protein adsorption fraction increases significantly from 9.22% to 20.68% (P < 0.05), and the zeta potential increases significantly from 25.7 mV to 27.1 mV (P < 0.05), respectively. Soy protein isolate shows resistance to bile salts displacement at the oil-water interface. In addition, the soy protein isolate modified by tea polyphenols is more difficult to be displaced by bile salts because of the strong electrostatic interaction and the thicker interface layer. Lipid digestion in intestine is an interfacial process. Exploring the interfacial displacement between protein and bile salts is beneficial to the study of lipid metabolism and food precise design.