Ultrasound-enhanced egg white proteins conjugated with polyphenols: The structure of the polyphenols on their functional properties

There is an urgent need for the development of a protein emulsifier with antioxidant and emulsifying properties. In this study, caffeic acid (CF), chlorogenic acid (CA) with a C3–C6 structure, epigallocatechin gallate (EGCG), catechin (CT), and quercetin (QE) with a C6–C3–C6 structure were conjugated to egg white protein (EWP) by using an ultrasound-assisted free radical method to create a dual-function emulsifier. Results indicated that ultrasound accelerated the interaction between EWP and CA, CT, CF, EGCG, or QE by strengthening the generation of hydroxyl free radicals and dispersion of EWP and polyphenols. The antioxidant activities of EWP were significantly improved after being induced by ultrasound-assisted CA, CF, EGCG, CT, or QE conjugation (p < 0.05), particularly modified by EGCG and QE with a C6–C3–C6 structure. The emulsifying properties of EWP were significantly improved after being induced by ultrasound-assisted CA, CF, EGCG, CT, or QE conjugation (p < 0.05), particularly modified by CF with a C6–C3 structure, it might be due to an increase in surface hydrophobicity, and this structural transformation has further improved the in vitro digestion efficiency of EWP. Therefore, the dual-function EWP emulsifier can be fabricated by the conjugation of polyphenols to EWP using an ultrasound-assisted free radical method.