Quality Change Of Different Fat Content Minced Beef During The Storage Time

In this study, longissimus dorsi as test material, added different proportions of fat (0%,10% and 20%), was minced into ground. After stir well, pallet packaging and high oxygen modified atmosphere packaging (78.8% O2,18.8% CO2 and 2.4% N2)two ways could be used.It stored respectively in the cold (-1.5℃) and low temperature (2℃). B0%, B10% and B20% indicated the ice temperature samples and L0%, L10% and L20% indicated refrigerated samples. Microorganisms, physical and chemical indicators could be evaluated during the storage. The fat content and storage temperature could effect on the water distribution and variation of water migration for ground which explored by low-field NMR techniques (LF-NMR) during storage. In addition, simulation of the actual storage of frozen ground beef sold in the transport process may occur repeatedly freezing and thawing, the test will be vacuum-packed frozen ground beef 5 thaw cycles, researched the times of repeated freezing and thawing effected on the quality of ground beef with different fat content changes. Specific results were as follows:1. Determine the microbial and physico-chemical indicators, which were processed by refrigerator and ice temperature storage of 0d,3d,6d,9d and 12d days, on different fat content of ground beef conducted by tray packaging, The results were that the total number of bacteria, psychrotrophic bacteria, TVB-N values and TBARS values in six groups of ground beef showed a clear upward trend during storage. L20% refrigerated 6d, total number of colonies and psychrophile exceeded 6.00 logcfu/g was the highest value for each treatment group. TVB-N values of the ice temperature group were lower than the national standard 20 mg/100g, while the refrigerated group storage for 12d. Fat Content had affected significantly on TBARS values, and the increased rate from high to low:L20%>B20%>L10%> B10%>L0%>B0%. LF-NMR could be used to detect the existing state and moisture migration. During storage, the number 6 group of samples T22 moisture change is small, T23 moisture freedom was increased, P23 free water content was increased.2. The different fat content of ground beef conducted by high oxygen modified atmosphere packaging. Then determine the microbial and physic-chemical indicators with refrigeration and ice temperature storage of 0d,3d,6d,7d. The results showed that 0%, L10% and L20% of total bacteria were higher than 6.00 logcfu/g, L20% group TVB-N value exceeds 20 mg/100g, TVB-N of the ice temperature group was lower than 20 mg/100g at Storage 6d. High oxygen modified atmosphere packaging promoted red ground beef (L* and a*) and brought more serious lipid oxidation. B10%, B20%, L10%, L20% of TBARS values were greater than 0.50 mg MDA/kg, the B0% and L0% compared to 0.27 mg MDA/kg and 0.33 mg MDA/kg. Ground beef conducted by high oxygen modified atmosphere packaging showed that the fat percentage was higher, easier for fat oxidation at 3d. By correlation analysis, the storage time were significantly correlated with TBARS value, high-speed rail myoglobin values, the total number of bacteria, psychrotrophic bacteria count, TVB-N value, drip loss, L*, a* value and b* (P<0.05), which could be used to evaluate the quality of high oxygen modified atmosphere packaging of ground beef.3. In order to simulate the actual phenomenon which the goods were processed by freezing and thawing repeated during transport. This test would be researched on the different fat content of ground beef conducted by vacuum packaging processed by freezing and thawing 5 cycles. Focused on the impact of the freezing and thawing number on quality of ground beef with different fat content. The results showed that with the number of freezing and thawing increased, TVB-N, TBARS and thawing loss rate of ground beef had a significant increasing trend (P<0.05), L* and b*were increased, a* was decreased. LF-NMR analysis found that with increasing the number of freeze-thaw, the T23 value of free water in three groups, F0%, F10% and F20%, had downward after 0-2 thaw, a significant increased in the degree of freedom. After 3 to 5 times of freezing and thawing, the free water flow started to decline slowly. It showed that repeated freezing and thawing caused cell damage and then the formation of ice crystals in multiple, destructed the molecular structure such that the loss of the integrity of the muscle fibers which led to loss of water.4. After 0-5 times repeated freezing and thawing of ground beef, myofibrillar proteins were extracted, measured a carbonyl group, a mercapto group and total protein solubility, and analysis the change of SDS-PAGE. The results showed that, with the increase of the number of freeze-thaw, myofibrillar protein oxidation deepening, performance in the carbonyl value had increased less total sulfhydryl content, protein solubility decreases. Compared with the former not thaw, carbonyl content increased by 1.54 to 1.76 times, mercapto group content was reduced to 26%to 31% and protein solubility decreased to 26% to 37%. Different proportions of fat had significant effect on the degree of oxidation of protein, in descending order of the degree of oxidation was F20%>F10%>F0%(P<0.05). SDS-PAGE showed that repeated freezing and thawing five times, molecular weight at 20～46 kDa could appear new bands small molecules and the protein bands became significantly thinner. Therefore, in the process of production and sale of ground beef filling, it should avoided temperature fluctuations which could decline in the quality of ground beef.