Conjugation of (–)‐epigallocatechin‐3‐gallate and protein isolate from large yellow croaker (Pseudosciaena crocea) roe: improvement of antioxidant activity and structural characteristics.

BACKGROUND: Large yellow croaker (Pseudosciaena crocea) roe is the main by‐product in the processing of large yellow croaker. Previous studies have found that its protein isolates are composed of vitellogenin, as well as vitellogenin B and C, having good functional properties. (‐)‐Epigallocatechin‐3‐gallate (EGCG) is a natural antioxidant component that can be combined with protein to improve antioxidant activity and structural characteristics of protein. RESULTS: EGCG was bound with the P. crocea roe protein isolate (pcRPI) by the free radical method to prepare the conjugate. The formation of pcRPI–EGCG conjugates was confirmed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and gel permeation chromatography, which showed that the calculated weight‐average molar masses of native‐pcRPI and pcRPI–EGCG conjugates were 86.9 and 215.3 kDa, respectively. The results of fluorescence, ultraviolet, circular and infrared spectra indicated that the conjugation of EGCG with native‐pcRPI changed the secondary and tertiary structure of native‐pcRPI. The pcRPI–EGCG conjugates exhibited higher thermal stability than native‐pcRPI. The radical scavenging and reducing power of native‐pcRPI were increased by 2.0–2.5‐ and 1.4‐fold, respectively, after the EGCG‐grafting reaction. CONCLUSION: These results indicate that the binding of pcRPI and EGCG effectively improved the antioxidant properties and structural characteristics of the pcRPI. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]