Effect of Protein Oxidation on Emulsifying Properties of Porcine Skin Gelatin

In order to investigate the effect of oxidation on the emulsifying properties of porcine skin gelatin, porcine skin gelatin was incubated with different concentrations of hydrogen peroxide (0, 10, 20 and 30 mmol/L) for simulated oxidation, and an emulsion was prepared by using the oxidized gelatin. The results showed that with increasing hydrogen peroxide concentration up to 30 mmol/L, the emulsifying activity index (EAI) increased from an initial level of 21.1 m²/g (unoxidized) to 34.3 m²/g. The emulsion stability index (ESI) decreased with the increase in hydrogen peroxide concentration. In addition, increasing oxidation degree led to an increase in the water contact angle of gelatin, which promoted the adsorption of gelatin at the oil-water interface and reduced the interfacial tension at the oil-water interface. Compared with the unoxidized group, the zeta potential value decreased from 9.61 to 5.94 mV after oxidation with 30 mmol/L hydrogen peroxide, indicating that the electrostatic repulsion between emulsion droplets decreased. Confocal laser scanning microscope (CLSM) showed that the emulsion droplets stabilized by oxidized gelatin was smaller in size. In summary, the oxidation treatment increased the hydrophobicity of gelatin, promoted its adsorption at the oil-water interface, and reduced the interfacial tension at the oil-water interface, which was conducive to the formation of smaller droplet size and enhanced the emulsifying activity of gelatin. However, the decrease in electrostatic repulsion between emulsion droplets increased the flocculation and aggregation of oil droplets and weakened the emulsion stability.