Research on the interface adsorption and emulsion properties of microwave cold plasma oxidized modified rice bran...

Rice bran protein (RBP) exhibits weak interfacial adsorption capacity due to its dense natural conformation. As a green non-thermal technology, microwave cold plasma can induce moderate oxidation and structural unfolding of RBP. Combined with the non-covalent interactions of polyphenols, the solubility and emulsifying properties of RBP can be further improved. In the study, oxidized RBP (ORBP) was used as the substrate to construct non-covalent complexes by regulating polyphenol phloridzin (PHL) addition levels, and the effect of complex structure changes on the interfacial properties of emulsion was investigated. The results indicated that PHL acted as a hydrogen donor, forming hydrogen bonds with ORBP. Compared to ORBP, the ORBP-PHL complex exhibited a trend of reduced α-helix and β-sheet, along with increased β-turn and random coil. PHL quenched the fluorescence of ORBP in an enthalpy-driven exothermic reaction, with ΔH = -67.288 kJ·mol^-1 and ΔS = -172.154 J·K^-1·mol^-1. When the concentration of PHL was 1 mg/mL, the complex exhibited minimal average particle size, PDI value, and turbidity, alongside maximum solubility. At this concentration, the interaction between PHL and ORBP further induced the ORBP structure to become flexible, and the attenuation rate of surface tension increased. The value of diffusion rate (K_diff) increased to 0.9038 mN·m^-1·s^-1/2, whilst the value of permeation rate (K_p) decreased to -2.6794 × 10^-4 s^-1. The exposure of more hydrophobic groups enhanced the affinity of ORBP to the oil phase, forming an interface membrane with stronger elasticity. At a PHL concentration of 1 mg/mL, the emulsion stabilized by the binary complex exhibited the smallest D_4,3 value and CI value, reaching 0.52 μm and 10.01% respectively. While the absolute zeta-potential, apparent viscosity, storage modulus, and loss modulus reached their maximum values. The emulsion with high storage stability and thermal stability was formed by the non-covalent interaction between PHL and ORBP. These findings provide a theoretical foundation and scientific rationale for expanding the application scope of RBP, as well as advancing its high-value and resource-efficient utilization.