Covalent conjugation of Inca peanut albumin and polyphenols with different phenolic hydroxyl numbers through laccase catalysis to improve functional properties

Abstract

BACKGROUNDEnzymatic crosslinking is a method that can be used to modify Inca peanut albumin (IPA) using polyphenols, and provides desirable functionalities; however, the effect of polyphenol structures on conjugate properties is unclear. In this study, we selected four polyphenols with different numbers of phenolic hydroxyl groups [para‐hydroxybenzoic acid (HBA), protocatechuic acid (PCA), gallic acid (GA), and epigallocatechin gallate (EGCG)] for covalent modification of IPA by enzymatic crosslinking, and explored the structure–function changes of the IPA–polyphenol conjugates.RESULTSSodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) analysis showed that laccase successfully promoted covalent crosslinking of IPA with polyphenols, with the order of degree of conjugation as EGCG > GA > PCA > HBA, the IPA–EGCG conjugate showed the highest polyphenol binding equivalents (98.35 g kg−1 protein), and a significant reduction in the content of free amino, sulfhydryl, and tyrosine group. The oxidation of polyphenols by laccase forms quinone or semiquinone radicals that are covalently crosslinked to the reactive groups of IPA, leading to significant changes in the secondary and tertiary structures of IPA, with spherical structures transforming into dense lamellar structures. The 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging ability and emulsification stability of IPA–EGCG conjugates improved by almost 6‐fold and 2.7‐fold, respectively, compared with those of unmodified IPA.CONCLUSIONThese data suggest that the higher the number of polyphenol hydroxyl groups, the higher the degree of IPA–polyphenol conjugation; additionally, enzymatic crosslinking can significantly improve the functional properties of IPA. © 2024 Society of Chemical Industry.