| As a new nature food preservative, Chitosan is produced by the deacetylation of chitin. it has been widely used in food, pharmaceuticals industry and so on for the advantage of nature, safe, nontoxic and high efficiency. So far, there are many studies on fresh-keeping fruits and vegetables with chitosan than meat and aquatic products. Tilapia,also known as Longevity fish, Carp of African, has been cultured all over the world.Tilapia is perishable food because of its high water content and nutrition, which leads to the short shelf-life and hinders the development of tilapia aquaculture. There has been some progress about preservation of meat and aquatic products on chitosan in recent years, but the refreshment of tilapia is still rare. In this paper, the effects of pH value,molecular weight and concentration of chitosan on antibacterial activity have been studied. And the effects of chitonsan with different molecular weight, concentration,chitosan mixture which consists of 200 ku chitosan and 4ku chitosan combined ozone water sterilization extending the shelf-life of filleted tilapia during refrigerated storage also have been studied. Specific contents and results are as follows:(1) The major factors of antibacterial activity of chitosan. Compare the antibacterial activity of chitosan with Escherichia coli of the factors of different molecular weight,concentration and pH value by inhibition zone and absorbance of bacterial suspension.The results show that the antibacterial activity of chitosan was inversely affected by pH(pH4.5-6.5 range tested), with higher activity at lower pH value, but it is the most reasonable experiment condition when pH value is 5.0. The research also show that there is a positive correlation between antibacterial activity of chitosan and concentration of chitosan within 1%, and chitosan mixture at a proper proportion has more antibacterial activity than the chitosan of single molecular weight.(2)Effects of chitonsan with different molecular extends the shelf-life of filleted tilapia during refrigerated storage. The sensory evaluation value, the total count of bacteria colonies, pH, volatile basic nitrogen(TVB-N value) and freshness indicators(K value) of Tilapia Fillets were measured during cold storage at 4?. The results showed that the sensory evaluation value of Tilapia Fillets treated with chitosan decreased slowly,and their total count of bacteria colonies, pH, TVB-N value, K value were lower than those of the control blank group. The self-life of Tilapia Fillets could be extended 1~3days during cold storage. The Tilapia Fillets treated with lower molecular weight chitosan(4 ku) has a better preservative effect.(3)Effects of chitonsan with different concentration extends the shelf-life of filleted tilapia during refrigerated storage. Compare the quality of tilapia fillets treated by chitosan(4 ku) at the different concentration of 0.5%,1% and 2%.The results show that the tilapia fillets treated with chitosan(4 ku) at the concentration of 1% has a better preservative effect, but the differences are not significant.(4)Effects of chitosan mixture combine ozone water sterilization extend the shelf-life of filleted tilapia during refrigerated storage. Investigate the total count of bacteria colonies of different parts of fresh filleted tilapia and the influence of different concentrations of ozone water sterilization. Besides, Effects of chitosan mixture, consist of 40% chitosan(4ku) and 60% chitosan(200ku), combined ozone water sterilization extends the shelf-life of filleted tilapia during refrigerated storage were researched. The results show that the total count of bacteria colonies of fresh tilapia filleted at the back less than others; ozone water sterilization can reduce the total count of bacteria colonies of fresh tilapia filleted effectively; The tilapia fillets treated with chitosan mixture have better ensory evaluation value, slow pH value change, lower TVB-N value and the total count of bacteria colonies,which indicate has a better preservative effect. |
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