Dose affected the role of gallic acid on mediating gelling properties of oxidatively stressed Japanese seerfish myofibrillar protein

The study investigated effects of gallic acid (GA, 0, 1, 5, 25 and 125 μmol/g) on properties of oxidatively stressed Japanese seerfish myofibrillar protein (MFP). Results showed that GA alleviated carbonyls formation and protected free amine. 5 μmol/g GA stabilized sulphydryls and secondary structure while 125 μmol/g GA enabled great loss of sulphydryls and reduced α-helix structure. Analysis of tryptophan fluorescence and surface hydrophobicity indicated that GA induced the unfolding of MFP structure but not in a dose-response fashion. Polymers were formed along with marked attenuation of myosin heavy chain in MFP with 125 μmol/g GA, and its particle size was the largest. Compared with purely oxidized MFP, MFP with 125 μmol/g GA showed a radical peak with narrower peak width but higher intensity. Results imply that high dose GA formed thiol-quinone adducts, enhancing polymerization. It also formed stable protein-bound phenoxyl radicals, inhibiting protein oxidation. Compared with non-oxidized group, storage modulus of MFP with 5 μmol/g GA increased sharply but that of MFP with 125 μmol/g GA decreased distinctly. The study suggests the role of GA on MFP depends much on its dose. Low dose GA could be used for improving fish MFP gelling property.