Study On Spoilage Microflora Change And Control Technologies In Chilled Mutton

Meat preservation has long been one of the problems demanding urgent solution inmeat industry development, which is also a key bottleneck inhibitting the marketabilityof chilled meat. In this paper, chilled mutton was looked as experimental material andseveral steps were carried out to inhibit the reproduction of spoilage bacteria. First of all,main types of spoilage bacteria were separated and identified primarily, and then initialmicroflora and its change during the storage were analyzed. Secondly, how differentways of package affected microflora change was studied. Thirdly, five antimicrobialswere selected to inhibit the growth of the main types of spoilage bacteria. Finally, anoptimum compound antimicrobial was obtained by three factors quadratic rotating designto prolong the shelf-life of chilled mutton. This paper not only provided a theory basis forthe farther research on the spoilage bacteria in the chilled mutton, but also could prolongthe shelf-life of chilled mutton to 42 days by treated with the optimum compoundantimicrobial, packed in modified atmosphere and stored at 4℃.1. Main types of spoilage bacteria in chilled mutton was separated and purified.With meat microbial identification manual, 21 Lactobacillus, 8 B. thermosphacta, 12Pseudomonas and 13 Enterobacteriaceae were primarily identified according to the formof bacteria, the characteristic of microflora and biochemical experiments. But there arealso 4 bacteria couldn't be identified with this method.2. Main types of spoilage bacteria in chilled mutton were incubated with selectiveagars to analyze initial microflora and its changes in vacuum condition. The resultshowed: Pseudomonas, Lactobacillus, B. thermosphacta and Enterobacteriaceae accountfor 90.50% of total bacteria counts, and their contents respectively were 29.25±3.07%,29.75±2.26%, 27.50±3.13% and 4.01±1.82%; Lactobacillus grew rapidly and fastbecame dominant microflora during the storage. However, Pseudomonas and B.thermosphacta decreased gradually. Enterobacteriaceae almost unchanged.3. Chilled mutton was packed with 5 types of atmospheres-air, 25%CO₂+75%N₂(MAP₁), 25%O₂+30%CO₂+45%N₂ (MAP₂), 70%O₂+20%CO₂+10%N₂ (MAP₃) andvacuum package. Main spoilage bacteria in chilled mutton were incubated with selectiveagars to analyze the effect of atmosphere on spoilage bacteria and the change of microflora during the storage. The result showed: in air package and MAP₃, because ofthe presence of oxygen, total bacteria count and all types of spoilage bacteria especiallyPseudomonas and Enterobacteriaceae were higher than other packages. Lowconcentration of oxygen or high concentration of CO₂ could inhibit the growth ofPseudomonas in vacuum package, MAP₁ and MAP₂. But Lactobacillus could grewrapidly and fast become dominant microflora. However, Enterobacteriaceae and B. ther-mosphacta were almost unchanged. In addition, Pseudomonas and Enterobacteriaceaewere more sensitive to CO₂ than Lactobacillus and B. thermosphacta. MAP₂ was the bestideal package to inhibit the growth of spoilage bacteria.4. Five nature antimicrobials-nisin, lysozyme, lactic acid sodium, tea polyphenol andchitosan-were selected to inhibit the growth of spoilage bacteria in chilled mutton. Maintypes of spoilage bacteria were incubated with selective agars to analyze the antisepticeffect of antimicrobials. The result showed: in the factor of antiseptic effect, nisin＞lysozyme＞lactic acid sodium＞chitosan＞tea polyphenol. Nisin and lysozyme couldinhibit the growth of gram-positive bacteria like Lactobacillus and B. thermosphacta.Lactic acid sodium could inhibit the growth of Pseudomonas well. In a certain extent, B.thermosphacta and Enterobacteriaceae could also be inhibited. Chitosan could inhibitthe growth of B. thermosphacta, Pseudomonas and Enterobacteriaceae. Tea polyphenolcould inhibit the growth of Pseudomonas.5. The concentration of the optimum compound antimicrobial constituted with nisin,lysozyme and lactic acid sodium were decided by three factors quadratic rotating design.Then its comprehensive preservation effect was inspected. The result showed: Nisin(0.38%)+lysozyme(0.27%)+lactic acid sodium(2.90%) could constitute the optimumcompound antimicrobials. By comparing in sensory evaluation, pH value, TVB-N valueand total bacteria counts, it was found that its comprehensive preservation effect wasbetter than others. So the formula of compound antimicrobial could be decided as Nisin(0.38%), lysozyme (0.27%), lactic acid sodium (2.90%). Chilled mutton treated with thiscompound antimicrobial, packed in 25%O₂+30%CO₂+45%N₂, and then stored at 4±1℃.At the 42 days, its each evaluation fit GB2708-1994 completely.