Effects Of Multiple Freezing And Thawing On Quality And Protein Oxidation Of Yak Meat

Yak is the special beef species in the alpine region,Its origin in the average altitude of3000 m above the remote areas,resulting from restriction of geographic factors and farming technologies,and fluctuations in temperature during sale,transportation and storage can cause repeated freezing and thawing of yak meat,frozen meat in the process of thawing juice loss and quality deterioration is very serious.Ongissimus dorsi were collected from 3 year-old Gannan yak,samples were randomly divided into 8 groups,each group is parallel three times,respectively,freeze-thaw 0,1,2,3,4,5,6,7 times.The effect of repeated freezing and thawing on the water holding capacity,protein oxidation and anti-oxidation of yak meat was analyzed,the effects of different freezing and thawing treatments on the nutrient composition of yak meat were analyzed,The microstructure of the yak meat during the repeated freezing and thawing process and the determination of the secondary structure of the protein,study on the mechanism of protein oxidation and quality in yak meat during repeated freezing and thawing.The test results are as follows1.With the increase of freezing and thawing times,pH,thawing loss,pressurized water loss rate and cooking loss,calcium activator activity decreased significantly(P<0.05),Nutrient content of water and crude protein,mineral elements,amino acid content decreased significantly(P<0.05),after 7 times freeze and thaw,the loss of essential amino acids in muscle is greater than that of nonessential amino acids,at the same time,the SRC value decreases with the increase of freezing and thawing times.Indicating that a number of freeze-thawing resulted in loss of juice in the yak meat,decreased tenderness,reduced nutritional quality.2.With the increase in freeze-thaw times,muscle fiber diameter and area significantly reduced(P<0.05),the proportion of cell gap increased significantly(P<0.05),after freezing and thawing mitochondria swelling and vacuolization,sarcomere shortening,Z line dislocation,or even disappear.Indicating that the freeze-thaw structure after its significant damage,yak meat quality decline.3.With the increase in the number of freezing and thawing,the carbonyl content in the muscle,the surface hydrophobicity of the protein increased significantly(P<0.05),sulfydryl content and protein solubility significantly reduced(P<0.05),indicating that the degree of protein oxidation with the increase in the number of freeze-thaw increased,the correlations among total phenolic content,RSA and TEAC were significant(P<0.05),were significantly4.decreased(P<0.05),indicating that the antioxidant capacity of protein decreased significantly with the increase of freezing and thawing times(P<0.05).It was also found that the correlation between water retention and protein oxidation and antioxidant activity was significant(P<0.05),it is shown that the freezing and thawing cycles cause the oxidation of yak meat to intensify,and the water holding capacity is reduced.5.The secondary structure of protein has changed with the increase of freezing and thawing times,?-helix content decreased by 62.01%,?-sheet content increased by 45.76%.Indicating that multiple freezing and thawing can significantly damage the secondary structure of the protein.In summary,in the storage and transportation system,in order to avoid the occurrence of freeze-thaw cycle,to ensure the quality of high yak meat processing is of great significance...