Ultrasound treatment modified the functional mode of gallic acid on properties of fish myofibrillar protein.

Effects of 0, 1, 5, 25 and 125 μmol/g gallic acid (GA) without or with ultrasound treatment (20 kHz, 400 w, 5 min) (NU or U groups) on properties of Japanese seerfish myofibrillar protein (MP) were studied. After sonication, tryptophan fluorescence decreased while surface hydrophobicity, free amine and SH content (not U125) and solubility increased. After heating, NU125 showed the heaviest polymers among NU groups, but U5 exhibited the strongest while U125 showed the weakest polymers in U groups. Storage modulus (G') of NU groups showed a dose-dependent style, but for U groups, U5 had the highest G' while U125 had the lowest G'. Mass analysis confirmed the formation of Cys-GA-Cys and Lys-GA-Lys polymers in U125. Thus, ultrasound promoted structural unfolding and reactive groups exposure, producing GA quinone by triggering OH·. These together led to the G' improvement by low dose GA but deterioration by high does GA.