Abstract: The sulfhydryl content, surface hydrophobicity, solubility, gel strength, water-holding capacity and rheological properties of myofibrillar protein (MP) added with different levels (0, 10, 50, 100 and 200 μmol/g) of gallic acid were measured. Also, the microstructure of the obtained gels was observed. The effects of changes in sulfhydryl content and surface hydrophobicity induced by gallic acid on the gel properties of MP were studied. The results showed that gallic acid caused a significant reduction of sulfhydryl content (P < 0.05), but there was no significant difference among different concentrations (P > 0.05). The addition of gallic acid significantly increased the surface hydrophobicity of MP (P < 0.05). The solubility increased significantly when gallic acid was added at 50, 100 and 200 μmol/g (P < 0.05). The gel strength and water-holding capacity of the MP gel with 10 μmol/g gallic acid were not significantly different from those of the control (P > 0.05) and the rheological curve was similar to that of the control. When gallic acid concentration increased to 50, 100 and 200 μmol/g, the gel strength and water-holding capacity decreased significantly (P < 0.05) and the rheological curve tended to be flat. The microstructure observation showed that when gallic acid concentration increased, the gel network structure was gradually loosened, showing bigger pores. Therefore, the low concentration of gallic acid (10 μmol/g) had no adverse effect on the gel properties of MP, while the medium and high concentrations of gallic acid (50, 100 and 200 μmol/g) impaired protein gelation and reduced the gel strength and water-holding capacity of MP gels, probably by promoting hydrophobic aggregation or the formation of thiol-quinone adducts.

Key words: gallic acid; myofibrillar protein; sulfhydryl group; surface hydrophobicity; gel properties