Ovalbumin-flaxseed gum dry Maillard covalent reaction improves the properties of the complex emulsion

This study constructed non-covalent and covalent complexes between ovalbumin (OVA) and flaxseed gum (FG) at ratios ranging from 5:1 to 1:5. The emulsion stabilized by the covalent OVA-FG complex at a 1:2 ratio (OF-C-1:2) exhibited the highest emulsifying activity and stability. Microscopic examination of the emulsion microstructure confirmed that OF-C-1:2 produced the smallest and most densely packed oil droplets. The rheological results show that OF-C-1:2 has a substantial viscosity value, with the G' and G" values being the closest, and both relatively large; thus, it exhibits good viscosity, elasticity, stability, spreadability, and compliance. The emulsions of each group were stored for 7 days. It was found that the emulsion of the OF-C-1:2 group had the best storage stability within 7 days. Characterization revealed that OF-C-1:2 had the highest grafting degree, the smallest free sulfhydryl groups, the lowest surface hydrophobicity, and a reduced particle size. Fluorescence and ultraviolet spectroscopy results suggested alterations in the tertiary structure, leading to reduced hydrophobicity and enhanced stability of the covalent complex. Infrared and circular dichroic spectroscopy analyses revealed that grafting primarily occurred at the side-chain amino groups, and the covalent complexes maintained their stability in the secondary structure. Correlation analysis indicated that the grafting degree, free sulfhydryl content, and zeta potential were highly correlated with both emulsifying activity and emulsion stability. This lays a solid foundation for applying emulsions in the food industry.