Changes In Microbial Diversity And Isolation Of Lactic Acid Bacteria During Salting And Fumigating Of Zhenba Bacon

Bacon is a kind of traditional Chinese cured meat products.It is widely popular in folk diets around the world because it has great variety,unique flavor,color and taste texture.In the fermentation process of bacon,microbial flora is a key factor affecting its flavor.In recent years,several studies have shown that lactic acid bacteria(LAB)are the dominant species in the fermentation process of bacon.Lactic acid bacteria consume carbohydrates to produce lactic acid,which can lower the p H of fermentation,inhibit the growth of harmful bacteria and prevent the spoilage of bacon.Some kinds of lactic acid bacteria can also produce flavor compounds to optimize the flavor and taste of bacon products.Zhenba County located in Shaanxi Province,has a northern subtropical monsoon climate,rich vegetation and excellent natural environment.With a long history of bacon production and mature production processes,Zhenba bacon has developed its own unique flavor and taste.Meanwhile,thanks to the development of sequencing technology,the methods to isolate and identify LAB strains with excellent fermentation performance for food and pharmaceutical products has become increasingly mature.Based on these,this study takes Zhenba bacon as the research object,explores the advantages of Zhenba bacon and the optimization of the production process,providing new ideas for the optimization of Zhenba bacon production By analyzing the microbial community structure,volatile substance composition and lactic acid bacteria isolated and screened from bacon samples and exploring their types and probiotic effects.The main experimental results obtained are as follows:1.The production and accumulation of metabolites and flavor substances in Zhenba bacon are influenced by processes and microbial diversity,and the salting and fumigating processes are main periods of their formation.In this study,the volatile substances of samples during salting,fumigating and finished product preserved for one year were analyzed with reference to the raw meat.The results showed that with the advancement of processing,the volatile substances varied greatly in different periods.And the salting and fumigating periods were key periods of volatile substance production.The volatile substances mainly produced in the salting process were terpenes and ethers,such as α-sideroprene,β-pinene and 1,8-eudesmol,while the fumigating process mainly produced aldehydes and phenolic compounds such as furfural,guaiacol and cresol.2.In this study,the microbial community composition on the surface of raw meat,salting and fumigating samples were analyzed by high-throughput sequencing.The bacteria with the highest overall abundance were Firmcutes and Proteobacteria,and the most abundant fungal phyla were Ascomycota and Basidiomycota.The dominant genus varied with advancement of processing steps.The dominant bacterial genus in raw meat was Escherichia-Shigella,and the dominant fungal genus was Fusarium.In salting period,the dominant bacterial genus evolved to Staphylococcus,Latilactobacillus,and Psychrobacter,and the dominant fungal genus evolved to Mortierella.Latilactobacillus and Debaryomyces have became the dominant bacterial and fungal genus during the fumigation period.As the salting and fumigating process progressed,the abundance of harmful bacteria decreased and the abundance of fermentation-friendly microorganisms increased,most of which were anaerobic or partly anaerobic in phenotype,and their functions were mainly focused on carbohydrate,lipid and amino acid metabolism pathways.3.A total of 16 LAB strains were isolated from the samples of Zhenba bacon during the salting period.Including Lactococcus garvieae S4-1～8,S8-1,Lactococcus lactis S8-2,S8-4,S8-6～8,Enterococcus faecalis S8-3 and Weissella viridescens S8-5.Four species of LAB were homotypic fermentation type,can not produce catalase and mucilage,all could effectively use cellobiose,mannitol,salicylic acid and maltose as carbon sources to produce acid.LAB strain S4-1 could also use inulin;strain S8-5 could also use sucrose and lactose;strain S8-3 could also use esculin hydrate,sorbitol,sucrose,inulin and lactose as fermentation substrates for acid production;strain S8-5 is unable to utilize all carbon sources except for cellobiose,mannitol,salicylic acid and maltose.4.Subsequently,this study was conducted to determine the performance of the dominant lactic acid bacteria in Zhenba bacon,and found that all four types of lactic acid bacteria have the characteristics of short growth delay period,long stability period,little difference in acid production performance,not hemolytic,good environmental adaptability and certain safety;all four experimental strains have a certain degree of bacterial inhibition ability,nitrite degradation ability,cholesterol-lowering ability and other functions,of which strain S4 1 has the strongest ability to degrade nitrite,strain S8-2 has the highest acid production efficiency,strain S8-3 has the best bile salt tolerance ability,and strain S8-5 has the best bacterial inhibition ability,cholesterol removal rate and self-aggregation ability.