The Effect Of Different Packaging Combined With Controlled Freezing-Point Storage On The Quality Of Beef

Controlled freezing-point(CFP) storage is a new method to fresh food which temperature ranges below 0℃ but the freezing-point in resent years. It can ensure food tissue integrity and also maintain its normal metabolism, inhibit the growth of microorganisms, thus it can achieve the effect of maintaining long-time freshness. This study mainly adopts the beef, dealing with air-packaging(AP), vacuum packaging(VP) and modified atmosphere packaging(MAP), in which the MAP is divided into two forms:MAP1 for high oxygen packaging (78.8%O2/18.8%CO2/2.4%N2) and MAP2 for no oxygen packaging (60%CO2/40%N2). They were storaged in -1.5℃ and 2℃ separately for retaining freshness, the sensory properties, microorgenisms, physicochemical properties. Meanwhile, Moisture distribution and the change of moisture migration in beef during storage were studied using by LF-NMR. The main conclusions were as follows:1. In the process of the whole storage, TVB-N value, TBARS value, MetMb and water loss tended to rise, but the rate was changes. Index of AP group was changing fastest and shelf life was shortest; MAP1 could better maintain the beef bright red color, but owing to the high concentration of O2, MetMb value and TBARS value increased significantly, and the shelf life was similar to AP group; MAP2 could effectively inhibit fat oxidation, maintain TVB-N value and MetMb at lower levels, but the color of beef was not good; TBARS value, TVB-N value and MetMb value of VP group were significantly lower than the previous packaging form, but water loss was bigger. No matter what kinds of packaging form, CFP storage (-1.5℃) was better than cold storage (2℃), it could maintain the color of fresh meat for a long time, reduce the cooking loss, inhibit fat oxidation and MetMb generation effectively.2. With the extension of storage time, the beef myofibril protein oxidation degree was deepening, carbonyl content was increasing, the total sulphur content was less and protein solubility was reducing, myofibril protein were aggregating and small pieces was deepening. The oxidation rate was AP>MAP1> MAP2>VP. And CFP storage (-1.5℃) compared with cold storage (2℃) could significantly inhibit protein oxidation.3. Based on low-field nuclear magnetic resonance (LF-NMR) technology, water changes in different packaging beef during the process of CFP storage was detected. The research result showed that with the extension of storage time, the existence of water which in beef changed, the ratio of water which not easy to flow gradually reduced, free water increased. This showed moisture migration happened in beef. In comparison, changes of AP group were most obvious, MAP was less than AP and VP group was better, MAP2 superior to MAP1. According to the correlation analysis, there was a certain correlation between P22 and T23 with storage time, cooking loss and water loss, so they could be used as index of water retention in beef.4. A high-performance liquid chromatographic hyphenated was developed for determination of eight kinds of biogenic amines (tryptamine, phenylethylamine, putrescine, cadaverine, histamine, tyramine, spermidine, spermine) in four kinds of packaging forms of beef during storage. The results showed that the amount of biogenic amines in different treatment group were increased with the extension of storage time, putrescine were the main biogenic amine, cadaverine and tyramine followed, typtamine, phenethylamine and hisamine were not checked out. And CFP storage could significantly inhibit formation of putrescine, cadaverine and tyramine. The species of biogenic amine in VP were the most. In 30 days storage, the total biogenic amine of 2℃VP was 110.17mg/kg and -1.5℃VP was 103.15mg/kg, they were higher than the other treatment group, but tyramine, putrescine and total biogenic amine content were both in limited range and consumption standard from security perspective. Meanwhile, with the extension of storage time, there was a significant positive correlation between formation of biogenic amine and the growth of microorganism through the correlation analysis. Among them, the putrescine could be used for the deterioration index of beef because there was a significant level (P<0.01) between it with microorganism.5. In the two storage temperature, the total number of bacteria and psychrophilic bacteria of four kinds of packaging forms of beef were both on the rise. AP group in 10 days, the total number of bacteria and psychrophilic bacteria were more than 6.00 (Lgcfu/g), but VP and MAP group could inhibit the growth of microorganisms. When storage in 25 days, the total number of bacteria in 2℃MAP2 was 6.45(Lgcfu/g) and-1.5℃MAP2 was 6.34(Lgcfu/g). The total number of bacteria and psychrophilic bacteria in VP were more than 6.00(Lgcfu/g) for value during 25～30 days in storage. So the shelf life of AP was 5 days, MAP1 was 10 days, MAP2 was 20 days and VP was 25 days.6. Compared with refrigerated storage, CFP storage which was the best effective method to fresh beef, could inhibit the growth of microorganism and the formation of biogenic amine in beef. It could maintain the beef color, tenderness, elastic and water retention in a long time. Meanwhile, it could effectively inhibit the oxidation of fat and protein.