To explore the effect of different levels of lipid oxidation on the structural and functional properties of myofibrillar protein (MP) in yak meat, the oxidation of side-chain amino acids, structure, rheological characteristics, and emulsion stability of MP incubated in the presence of different concentrations (0, 0.1, 1, 5, 10 and 20 mmol/L) of malondialdehyde (MDA) were measured. The results showed that with an increase in MDA concentration, the contents of carbonyl group, MDA-MP adducts and dimeric tyrosine and the relative content of β-turn in MP overall increased, while total sulfhydryl content, surface hydrophobicity, endogenous fluorescence intensity, and the relative contents of α-helix and β-sheet decreased. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results indicated gradual loss of myosin heavy and light chains, implying that interaction with MDA could induce MP oxidation and cross-linked aggregation and result in structural transition from an ordered to a disordered state. In addition, moderate oxidation (with MAD concentration < 10 mmol/L) increased the storage and loss moduli and improved the gel quality of MP; however, excessive oxidation (with MAD concentration ≥ 10 mmol/L) led to serious aggregation of MP and a decrease in the storage and loss moduli as well as a decrease in the emulsion stability and color deterioration. In conclusion, MDA oxidation can promote the oxidation of MP, and alter the structural and functional properties.

Sarcoplasmic proteins (SP) derived from yak meat were oxidized by malondialdehyde (MDA) at different concentrations. The effects of lipid oxidation on physicochemical properties and color stability of SP were investigated by evaluating side-chain amino acid oxidation, protein structure and color of SP and the oxidation status of myoglobin (Mb). The results showed that after MDA oxidation, the a* value, b* value, C* value, and deoxymyoglobin and oxymyoglobin contents of SP significantly decreased (P < 0.05), and the L* value, metmyoglobin content, and ferrylmyoglobin concentration significantly increased (P < 0.05), indicating that MDA oxidation lowered color stability. The contents of carbonyl groups and dimeric tyrosine, the fluorescence intensity of SP-MDA adducts, and the relative contents of β-helix and β-turn significantly increased (P < 0.05), and total sulfhydryl content, surface hydrophobicity, intrinsic fluorescence intensity, and the relative contents of α-helix and random coil significantly declined (P < 0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed blurred expansion of small molecule bands and the formation of macromolecular aggregates, suggesting that MDA promoted the oxidation and aggregation of SP. Pearson correlation analysis revealed significant correlations between MDA oxidation and physicochemical properties and color stability of SP (P < 0.05). This study reveals that MDA alters the structure of SP by directly oxidizing it or mediating Mb oxidation, causing cross-linked aggregation of SP and reducing its color stability.