Effect Of Map Combined With Nutural Perservative On Quality And Bacterias Of Large Yellow Croaker(Pseudosciaena Crocea)

Large yellow croaker (Pseudosciaena crocea) is one of the most important marine-cultured fish species in China,which is rich in protein, unsaturated fatty acids, vitamins, and inorganic substance, etc in muscle. The content of crude protein is about18%and crude fat is11%. During the storage after the death of fish, due to the complex physiological and biochemical reaction and the growth of microorganisms, the quality of fish decrease quickly and cause the degration of fish, then following the spoilage and the decline of the sensory quality. Therefore, to research the method of preservation technology of large yellow croaker is still a problem to be solved.In view of the above-mentioned facts, the large yellow croaker was studied to evaluate the qualities by the microbial, physicochemical and sensory parameter,this paper studied the effect of Modified atmosphere package (MAP) on the quality of large yellow croaker, based on this, MAP combine with natural preservative to further evaluate the quality changes during the large yellow croaker and mechanism of compound fresh-preserving.1、Compared to air package and vacuum package, MAP can improve the quality of large yellow croaker stored at4℃. The result showed that MAP could inhibit the growth of TVC effectively, maintained a good sensory quality of large yellow croaker, at the same time, Pseudomonas spp. and H2S-producing bacteria were significantly decreased, TVB-N was delayed, maintained the low pH and steady hardness and elasticity, but the drip loss was obvious. At15days, the TVC was6.15log10cfu/g, TVB-N was25.76mg/100g. The shelf life of AP, VP, MAP was5,10and15d respectively. Therefore, MAP has a good effect on inhibiting the growth of special spoilage and keep good quality in the result of extending shelf-life.2、The effect of MAP combined with tea polyphenols, Nisin and chitosan coatings on large yellow croaker is better than MAP and single natural preservatives. During the storage, MAP+Ch+TP+Nisin, Ch+TP+Nisin and MAP group can reduce the initial TVC of large yellow croaker and inhibit the growth of5spoilage bacteria, at the end of shelf life, the TVC of MAP+Ch+TP+Nisin group was less than3log10cfu/g. Three treatment group can inhibit the increase of pH and k value, accumulation of TVB-N, maintained low TBA value, delayed the changes of sensory quality, especially MAP+Ch+TP+Nisin group, which can also decrease drip loss. Basd on the evaluation of TVC， physical and chemical parameters (TVB-N, k value, TBA) and sensory parameter, the shelf life of control, Ch+TP+Nisin, MAP, MAP+Ch+TP+Nisin were4-5d,8d,16d and20d respectively. And during the refrigerated storage, MAP act as main role in the MAP combine with compound preservative treatment.3、After Analysing6kinds medium on evaluation the TVC of large yellow croaker, the TVC of TSA is the highest, at the end of storage the TSA, NA, PCA, LH and CFC were similar, but the TVC of IA was slightly lower. The result showed TSA was best to evaluate the TVC of large yellow croaker.16S rDNA PCR amplification and sequencing were applied in researching the bacteria phase change of large yellow croaker. The large yellow croaker initial bacteria is diverse, mainly included Shewanella (25%), Pseudomonas (25%), Vibrio anguillarum (25%), Serratia, psychrophilic bacteria, Aeromonas. As the extension of storage time, the diversity of bacteria decreased, mainly included Shewanella (71.5%), Vibrio anguillarum (9.5%), Serratia, Pseudomonas, Enterobacterium, Aeromonas among which Shewanella baltica is dominant bacteria. After obtaining the DNA of bacteria, PCR-DGGE was applied to analyse the bacteria phase change. Comparing to cultured methods, the DGGE profiles of direct extraction from the fish was more diverse, but the main band was less obvious than cultured methods. On the other hand, the band of treatment group was fewer and less lightly than control group, but the main band was similar. The result of tapping sequencing showed that the main band was all Shewanella, including Shewanella. baltica, Shewanella. frigidimarina and Shewanella. putrefaciens. The result of16S rDNA PCR sequencing and tapping sequencing was similar. Selective culture methods,16S rDNA PCR and PCR-DGGE proved Shewanella is dominant spoilage bacteria and Compound preservative treatment could inhibit these bacteria and have a effect on bacteria phase.