Effects of Protein Oxidation and NaCl Concentration on the Structure of Yak Myofibrillar Protein under Different pH Values

In this study, the effects of protein oxidation and NaCl concentration on the structure of yak myofibril protein (MP) were investigated. To this end, MP was oxidized for 1 h in a Fenton oxidation system and treated for 1 h with different NaCl concentrations under three pH values (5.0, 6.0 and 8.0), respectively. The total sulfhydryl content, surface hydrophobicity, solubility, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern, and microstructure of treated MP were determined. The results showed that at a fixed pH, the total sulfhydryl content and solubility decreased with increasing H₂O₂ concentration, and the surface hydrophobicity increased. In addition, the degree of expansion declined horizontally. At a fixed H₂O₂ concentration, the total sulfhydryl content and solubility increased with increasing pH, and the surface hydrophobicity decreased, accompanied by lateral expansion, narrowing of the A-band and destruction of the Z-line. At a fixed pH, the solubility increased with increasing NaCl concentration, and the surface hydrophobicity decreased, accompanied by lateral expansion and destruction of the transverse bridge. At a fixed NaCl concentration, the solubility increased with increasing pH, the surface hydrophobicity decreased, and lateral expansion occurred. At pH 8.0 and 1 mol/L NaCl concentration, both the M-line and Z-line were obviously destroyed, the structure of MP became blurred, the myotome was broken, the transverse bridge was destroyed, and coarse filaments were separated from fine ones. In conclusion, both protein oxidation and NaCl had adverse effects on yak MP under different pH conditions, and protein oxidation had the lowest negative impact on MP structure at pH 6.0 and a NaCl concentration of 0.4 mol/L.