Abstract: Abstract: Air packaging (AP), vacuum packaging (VP) and modified atmosphere packaging (MAP) have been widely used during chilled storage in retail meat market. However, different packaging has its advantage and disadvantage. AP can get desirable red color in a short time, but protein oxidation and lipid oxidation occur during cold storage. VP keeps a stable purple color and increases the shelf life of fresh meat. However, VP can cause liquid exudation and product deformation of fresh meat. MAP with 80% oxygen can maintain desirable and stable cherry red color of fresh meat and extend the shelf life of fresh beef. Nevertheless, it can possibly cause protein oxidation and lipid oxidation of fresh meat during chilled storage. Protein oxidation is the covalent modification of proteins induced by reactive oxygen species or by-products of oxidative stress. Previous researches have demonstrated that protein oxidation inhibits μ-calpain activity, which may influence the rate and degree of protein degradation of fresh meat. The aim of this study was to examine effects of AP and high-oxygen MAP (80% O2 + 20% CO2) on the tenderness of beef samples during postmortem cold storage using VP as control. Six longissimus dorsi muscles of Simmental purebred yellow cattle were precooled at 4℃ for 24 h, which were then randomly assigned to MAP, VP and AP, and stored for 0, 4, 7 and 10 d respectively at 4℃. The carbonyl content and distribution, the values of protein surface hydrophobicity, the solubility values of myofibrillar protein, sarcoplasmic protein and total protein, and the degradation of desmin and titin were determined, respectively. The results showed that AP and MAP presented the stronger fluorescence light signal in a peripheral area, and the fluorescence light signal spread to the internal cellular environment, which showed that the extent of protein oxidation increased. The values of protein surface hydrophobicity of beef samples from AP and MAP were significantly higher than that of the samples from VP (P<0.05), while the protein solubility values of beef samples from AP and MAP were significantly lower than that of the samples from VP 10 d after the storage (P<0.05). The degradation of desmin and titin of beef samples from AP and MAP was significantly lower compared to the VP 7 and 10 d after the storage (P<0.05), which showed protein oxidation further inhibited the degradation of desmin and titin. Increased protein oxidation under AP and MAP inhibits the degradation of the key protein during postmortem cold storage.