Microbial Community Succession And The Quality Changes During Spontaneous And Inoculation Fermentation Of Stinky Mandarin Fish(chouguiyu)

Mandarin fish(Siniperca chuatsi)is a kind of common edible fish and one of the “four freshwater fish” in China.Chouguiyu is a kind of traditional fermented product with a unique flavor that is made from fresh mandarin fish as raw material.In this paper,Chouguiyu as the research object,and use of orthogonal experimental design to optimize the traditional Chouguiyu fermentation process and the sensory evaluation was used to determine the optimal fermentation process conditions.The changes of microorganisms,volatile base nitrogen(TVBN),thiobarbituric acid(TBA),and volatile flavor compounds were examined during the fermentation of Chouguiyu.Through experiments,the traditional Chouguiyu fermentation process was optimized,and Chouguiyu fermentation was conducted using the starter culture,which provided a reference for the industrial production of Chouguiyu and the preparation of starter culture.This topic is mainly studied the following aspects.1.The fermentation time,fermentation temperature and salt content as experimental factors,an orthogonal test was designed to optimize Chouguiyu fermentation process.The sensory evaluation and validation tests yielded superior fermentation process conditions: fermentation temperature 12 °C,salt 6% and fermentation for 7 days.Analysis of the basic components of fresh mandarin fish and Chouguiyu revealed that the content of water,crude fat,crude protein and total sugar of mandarin fish decreased after fermentation.The results of 16 S rDNA sequencing showed that the changes of Fusobacteria,Cyanobacteri and Proteobacteria before and after fermentation were the most significant in chouguiy.The change of microorganisms could cause the change of volatile substances.Use E-nose and GC-MS analysis of volatile components of fresh and fermented mandarin fish showed that volatile flavor components had greatest changes.2.The microorganisms,TVB-N,TBARS,pH value,texture(TPA)and volatile flavor substances were detected during the fermentation process of Chouguiyu.The results showed the hardness,gumminess and chewiness increased first in the fermentation process.On the fourth day of fermentation,Oceanisphaera,psychrilyobacter,Fusobacterium and Arcobacter increased,and the detection results of E-nose and GC-MS also showed significant changes.These microorganisms may play an important role in the formation of flavor and quality of Chouguiyu.PCA analysis of microorganisms and fermentation time showed that the microorganisms in the fermentation system tend to be similar with the prolongation of fermentation time.E-nose and GC-MS result with fermentation time,microorganisms for redundancy analysis(RDA)respectively.In the early stages of fermentation,Vibrio and Photobacterium related closely to aldehyde and aromatic compounds,while in the later stages,Oceanisphaera,Pseudoalteromonas,Psychrilyobacter,Fusobacterium and Arobacter are the main microorganisms which produced ester,hydrocar,aromatic,alcohols,ketones,acids and nitrogen compounds.GC-MS results using odor activity values(OAVs>1)determined that the aroma-active compounds(AACs)were 1-octen-3-ol,linalool,2-methyl-3-octanone,piperitone,hexanal,heptanal,nonanal,indole,and anethole.3.L.lactis M10 and W.cibaria M3 isolated from Chouguiyu were used to inoculate the mandarin fish,and the starter culture groups: L(L.lactis M10),W(W.cibaria M3),LW(L.lactis M10 and W.cibaria M3)and control(no any starter culture).It was found that L.lactis could quickly establish advantage in the fermentation system,and there was competition between L.lactis and W.cibaria,and the starter culture could inhibit the growth of other microorganisms.The contents of TVB-N,TBARS and biogenic amines in the inoculation group were lower than control group,indicated that the strains could inhibit the accumulation of TVBN,TBARS and biogenic amines.E-nose and GC-MS results showed that L.lactis had a greater influence on the flavor in the early fermentation stage,and the LW group was most similar to the Control 7 sample in the late fermentation stage.The sensory evaluation score of the LW sample was the highest,and it showed that Inoculation the mixed bacteria LW can shorten the time required for the fermentation of the Chouguiyu.4.The products obtained from the fermentation of old soup were detected by microorganisms,TVB-N,TBARS,TPA,and flavor substances.A.bestiarum,M.morganii and V.fluvialis were the main bacteria in the Basa fish samples.The dominant species were A.bestiarum,Aeromonas sp,A.veronii and V.fluvialis in mandarin fish samples.TVB-N and TBARS values of the 6 groups old soup fermentation samples were all lower than those of the normal 7d samples,and the pH was higher than the 7d samples.The texture of the Basha fish was significantly lower than that of the 7d samples,and the texture of the mandarin fish sample remained basically unchanged.It was indicated that controling the same amount of bacteria per round cannot produce similar product to Chouguiyu.Based on the above research resulted,the optimized fish fermentation process can be used for the industrial production of Chouguiyu.However,traditional fermented Chouguiyu products have some hidden safety and health hazards.Inoculation starter culture can effectively inhibit the production of harmful microorganisms and biogenic amines,improve the quality of Chouguiyu,and provide a solid theoretical basis for safe and sanitary industrialized production of Chouguiyu.