To extend the storage period of frozen Tibetan mutton,Tibetan mutton from Qinghai was used as the test material.The total bacterial count,pH value,color stability,water-holding capacity,thiobarbituric acid(TBA)content,peroxide value(POV),and myofibrillar protein oxidation were measured.The quality changes of Tibetan mutton stored at-18 ℃ for 0,3,7,15,30,60,and 90 days were investigated under treatments with different packaging materials:nylon composite bags(PA/PE),polyester composite bags(PE/PET),and seven-layer co-extrusion bags(PA/TIE/PA/TIE/PE/PE/PE).The results showed that compared with standard fresh-keeping bags,the three tested packaging materials,combined with vacuum packaging,had a significant effect on the quality of frozen Tibetan mutton.PA/PE bags could help preserve the quality of the mutton more effectively.After 90 days of freezing,the total number of colonies decreased by 1.7 lg CFU/g in the PA/PE bags compared with the standard storage bags.The pH value was in the range of 6.2～6.6,and the color stability was superior.The cooking loss rate,thawing loss rate,and centrifugal loss rate increased by 4.51％,0.93％,and 2％.The TBA and POV values were significantly lower in the PA/PE bags than the standard storage bags,showing reductions of 0.78 mmol/kg and 0.033 mg/100 g,respectively.The carbonyl content of myofibrillar protein decreased by 1.63 nmol/mg,the sulfhydryl group content decreased by 0.21 nmol/g,and the surface hydrophobicity decreased by 6.74 μg.Comprehensive analyses showed that the PA/PE bag combined with vacuum packaging,while storing at a temperature of-18 ℃,can effectively maintain the quality of frozen Tibetan mutton and prolong its shelflife.
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