Changes In Refrigeration Quality Of Lateolabrax Japonicus Fillets And Isolationidentification Of Its Specific Spoilage Organisms

Aquatic products are rich in high-quality protein,polyunsaturated fatty acids,multivitamins and minerals,low in cholesterol,and have won the favor of consumers with their unique color,fragrance and taste.In 2018,China's annual aquatic product output reached 64.576 million tons.However,the microorganisms and highly active enzymes in the aquatic products can easily change the quality,color,and taste,and cause economic loss.According to statistics,more than 30%of catches are not consumed every year due to spoilage.Therefore,in the process of fishing,storage,transportation and processing of aquatic products,in order to ensure the nutritional value of aquatic products and reduce spoilage,the preservation of aquatic products is very important.As the most commonly used low temperature preservation method,refrigerated preservation can ensure the quality of aquatic products,and avoid freezing the ice to damage the fish fillet tissue and oxidative browning of protein and fat.Lateolabrax japonicus,commonly known as sea bass,is a member of the Perciformes,Percoidei,Percichthyidae and Lateolabrax.As the main marine aquaculture fish in China,there are few studies on its preservation and processing,resulting in a large degree of waste of fish meat and its by-products.Therefore,in this study,the fillets of Lateolabrax japonicus were used as materials,and three aspects of research were carried out.First,the quality changes and quality correlation of the vacuum-packed Lateolabrax japonicus fillets refrigerated at 4? and the shelf life of it was determined.Secondly,the spoilage bacteria at the end of the shelf life of Lateolabrax japonicus fillets were isolated,purified and identified under 4? refrigerated conditions,and the rotten ability of Specific Spoilage Organisms was studied by artificial inoculation of sterile fillets.Finally,the effect of impregnation with biopreservative tea-polyphenols on the quality change of Lateolabrax japonicus fillets refrigerated at 4? was studied.The purpose is to further clarify the action mechanism of tea polyphenols in slowing down the quality deterioration of refrigerated Lateolabrax japonicus fillets and inhibiting the growth and reproduction of Specific Spoilage Organisms,and to provide theoretical support for the specific antibacterial preservation and processing of refrigerated Lateolabrax japonicus fillets.The main research contents and conclusions are as follows:1.Studies on the quality change and quality correlation of vacuum-packed Lateolabrax japonicus fillets refrigerated at 4? show that:the physical,chemical and sensory qualities of vacuum-packed Lateolabrax japonicus fillets refrigerated at 4? continued to deteriorate,reaching the end of the shelf life on the 9th day of storage.Under 4? refrigerated conditions,the water holding capacity and whiteness of Lateolabrax japonicu fillets continued to decrease,the TBA value and the total number of colonies significantly increased,and the p H decreased first and then increased.Correlation analysis found that in addition to water holding capacity,the trends in p H,whiteness,TBA,and total colonies were significantly correlated with sensory comprehensive scores.On the 9th day of storage,the total number of colonies of refrigerated Lateolabrax japonicus fillets exceeded the secondary freshness standard[6log?CFU?/g].The overall sensory score was lower than 6.0,which was unacceptable to the end of the shelf life.2.Eleven strains were isolated from the spoilage bacteria of vacuum-packed Lateolabrax japonicus fillets refrigerated at 4?.Among them,PCA medium,CFC medium,VRBA medium,MRS medium,IA medium,BP medium,and Bengal red medium were 4,1,3,2,1,0,0,and 0 strains,respectively.When the DNA of the above strains were amplified and sequenced,one sample in PCA medium was amplified without bands for multiple times and could not be sequenced;two samples in VRBGA medium had binding problems,and the sequencing results could not be stitched and compared;8 samples could be sequenced and stitched and compared Effective BLAST.The eight strains obtained from the strain identification were:Staphylococcus warneri,Staphylococcus sp.,Shewanella,Klebsiella aerogenes.Enterobacter aerogenes,Delftia tsuruhatensis,Leclercia adecarboxylata,and Moraxella osloensis are classified as Pseudomonas on the genus level Pseudomonas,Enterobacter,Staphylococcus,Shewanella,Leclercia and Delftia.3.Studies on the rot-causing ability of Specific Spoilage Organisms in vacuum-packed Lateolabrax japonicus fillets refrigerated at 4? showed that:Shewanella and Enterobacter aerogenes had the highest rot ability,and were the Specific Spoilage Organisms in refrigerated Lateolabrax japonicus fillets.By artificial inoculation of sterile fish fillets and preliminary screening of sensory scores,it is considered that Enterobacter aerogenes,Staphylococcus warneri,Shewanella and Moraxella osloensis have strong ability to cause spoilage that can be used for the study of the spoilage abilities of Specific Spoilage Organisms.Then,the water holding capacity,p H,TBA value,TVB-N value,total number of colonies and the yield factor Y_TVB-N/CFU and Y_TBA/CFU of Lateolabrax japonicus fillets after inoculation with different spoilage bacteria were calculated.The results showed that Shewanella and Enterobacter aerogenes were the Specific Spoilage Organisms in refrigerated Lateolabrax japonicus fillets.4.Studies on the quality change of vacuum-packed Lateolabrax japonicus fillets impregnated with tea polyphenols show that:Tea polyphenol impregnation can effectively slow down the quality deterioration of refrigerated Lateolabrax japonicus fillets and extend the shelf life of fillets by 12 d.Lateolabrax japonicus fillets were vacuum-packed after being impregnated with a 3%tea polyphenol solution and refrigerated in a refrigerator at?4±0.5??.Through a comprehensive analysis of the sensory,physical and chemical qualities?water holding capacity,p H,whiteness,TBA value and total number of colonies?of Lateolabrax japonicus fillets during storage,it can be found that:except for the whiteness value,the physical and chemical qualities of the fish fillets treated with tea polyphenols were basically the same as those of the fillets that were not impregnated with tea polyphenols,but the indexes of fish fillets impregnated with tea polyphenols changed much more slowly.Combining the results of the senses and the total number of colonies,it can be considered that the Lateolabrax japonicus fillet impregnated with tea polyphenol reached the end of shelf life on the21st day.Compared with the non-tea polyphenol impregnation treatment,the shelf life of Lateolabrax japonicus fillets was prolonged by 12 d.