Effect of Protein Oxidation on the Structure and Water-Holding Capacity of Yak Muscle under Low Salinity Environment

In an effort to elucidate the effect of protein oxidation on its water-holding capacity (WHC), yak muscle was treated in a Fenton oxidation system containing 0.1 mol/L NaCl at pH 5.0 or 8.0. The results showed that the contents of malondialdehyde (MDA) and carbonyl groups overall increased with increasing concentration of H₂O₂ in the Fenton system, and the total sulfhydryl content decreased, which reflects an increase in the degree of oxidation. The contents of MDA and otal sulfhydryl groups were higher at pH 5.0 than that at pH 8.0. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) displayed that the oxidation induced backbone breakage and covalent cross-linking by disulfide or non-disulphide bonds of myofibrillar proteins. As a result, the space between muscle structures was reduced and the WHC decreased, which was manifested by an increase in centrifugation loss and cooking loss. Transverse relaxation times (T₂) from low-field nuclear magnetic resonance (NMR) and microstructure analysis by scanning electron microscopy (SEM) demonstrated that as the degree of oxidation increased, the content of immobilized water decreased, the content of free water increased, and the microstructure was damaged, causing water loss from the muscle. Under the same oxidation conditions, the centrifugation loss, cooking loss and free water content were lower at pH 8.0 than at pH 5.0, which illustrated that yak muscle had higher WHC at pH 8.0.