Conjugation of coconut protein with ferulic acid promotes interfacial adsorption and mitigates lipid oxidation in O/W emulsion

The formation of small droplets in emulsion systems promotes lipid oxidation, affecting their shelf life. In this study, ferulic acid was covalently grafted onto coconut protein (CPI) through alkaline treatment method. The structural characteristics, interfacial properties, emulsifying properties, and oxidative stability of emulsions prepared by coconut protein-ferulic acid covalent complexes (CPF) were investigated. The results showed that covalent grafting of ferulic acid could change the physicochemical properties of coconut protein, including altering protein secondary and tertiary structures, enhancing the absolute value of zeta potential and antioxidant activity [2, 2-diphenyl-1-picrylhydrazyl (DPPH • ) and 2, 2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS •+ )]. Meanwhile, the interfacial behavior of CPI and CPF was characterized by dissipative quartz crystal microbalance and dilatational rheology analysis. Compared to CPI, CPF could diffuse to the oil-water interface quickly (from 0.084 ± 0.002 to 0.154 ± 0.003 mN/m/s 1/2 ), and formed a thick interfacial layer dominated by elasticity, which enhanced the centrifugal stability of CPF-stabilized emulsions and effectively inhibited lipid oxidation within a 15-day storage period. Our results clearly demonstrated that coconut protein-ferulic acid conjugated complexes could improve emulsion stability and mitigate lipid oxidation, owing to the strong electrostatic repulsion interaction and high diffusion rate at interface. These findings may provide comprehensive insights for the further design and development of protein-polyphenol covalent complexes in the food industry.