Microbial Population Structure Analysis And Mixed Bacteria Starter Preparation Of Zhanjiang Traditional Fermented Trachinotus Ovatus

The Trachinotus ovatus is a popular and common fish food because it has the characteristics of thick meat,fresh taste and tenderness,and also has high nutritional value.In recent years,with the high rate of return on the economic benefits of Trachinotus ovatus breeding,the amount of Trachinotus ovatus breeding has continued to increase.Since 2016,the amount of Trachinotus ovatus farming in the Zhanjiang market has far exceeded market demand,and the supply of fresh products has been slow for many times.Therefore,there is an urgent need to develop fish processed products represented by fermented Trachinotus ovatus,to ease the pressure of fresh fish sales,enrich the diversity of products,and increase the total sales.At present,traditional fermented Trachinotus ovatus rely on the fermentation of naturally enriched microorganisms,and the microorganisms involved in the fermentation are unstable,resulting in extremely unstable product quality and hindering the large-scale production of the industry.In order to change the defects of unstable quality,low storage and low production efficiency,it is necessary to in-depth research on traditional fermented Trachinotus ovatus.In this thsis,high-throughput microbial sequencing technology was used to analyze the microbial population structure of traditional fermented Trachinotus ovatus in Wushi Town,Leizhou City,Guangdong Province.Fermentation strains are screened out using traditional isolation techniques,and then their biological characteristics are studied.The flavor and taste measured by the electronic nose and electronic tongue are used as evaluation indicators,and the artificially inoculated mixed bacteria starter was developed to provide a basis for large-scale industrial production.The main research contents and results are as follows:(1)Analyze the microbial population structure of fermented Trachinotus ovatus by high-throughput metagenomic microbial sequencing technology.After quality control of Miseq sequencing sequence,chimera removal and non-characteristic amplification,all aspects of data analysis were carried out.Experiments show that there are 2142 OTUs in total,among which Chao1,ACE,Shannon and Simpson are 16,508.33,43682.36,2.09 and 0.30 respectively.The genus level analysis detected a total of 39 microbial genera,of which 6 were the most dominant bacteria genera,ranging from high to low: Cobetia,Pseudoalteromonas,Salt Salinivibrio,Psychrobacter,Vibrio and Halolactibacillus.(2)Isolation and biological characteristics of dominant strains of fermented Trachinotus ovatus.Separate the Trachinotus ovatus strains by flat coating method,pass Gram staining and microscopic examination,catalase test,fermentation glucose acid production test,fermentation glucose gas production test,salt tolerance test,histamine test,antibacterial test,Screening out eligible fermentation dominant strains,the dominant strains are three: ZJ-02(Pediococcus pentosaceus),TJ-07(Lactobacillus plantarum)and QJ-05(Saccharomyces rouxii).Then,the biological characteristics of the three dominant strains of fermented Trachinotus ovatus were studied.Results show that: 30 ?,pH 5?6,NaCl content 0?5% is the most suitable for the fermentation growth of the three strains;the nitrite content in the fermented Trachinotus ovatus does not affect the growth of Saccharomyces rouxii;In the mixed fermentation broth,Lactobacillus plantarum is the main inhibitor to Escherichia coli and Staphylococcus aureus;in the aroma evaluation of the mixed fermentation broth,methyl,sulfide,nitrogen oxides,alcohols or aldehydes and ketones Organic aromatic sulfides play an important role.The main aroma contribution is Pediococcus pentosaceus;the main contribution of umami in the mixed bacteria fermentation broth is Pediococcus pentosaceus;the main acidity contribution is Lactobacillus plantarum.(3)Three fermentation strains were mixed in different proportions and configured as a starter,and the purchased fresh Trachinotus ovatus was artificially inoculated and fermented.Using electronic nose PCA and radar chart analysis method to analyze 10 kinds of odors such as aromatic benzene,aromatic ammonia,sulfide,and nitrogen oxide on fermented products under different starters.The electronic tongue is used to analyze8 tastes of fermented products,including sour,sweet,bitter,and astringent.Experiments show that the flavors formed by single-strain fermentation are not much different;when Lactobacillus plantarum: Saccharomyces rouxii: Pediococcus pentosaceus = 0:1:2,the electronic nose detects the highest sulfide odor,and the electronic tongue detects higher umami and aftertaste,and the sourness and bitterness are lower.Therefore,the ratio of Lactobacillus plantarum: Saccharomyces rouxii:Pediococcus pentosaceus = 0:1:2 is the best mixture of starter.