Whole Genome Sequence Analysis Of Leuconostoc Mesenteroides FX6 And Its Effect On Flavor Quality Of Soybean Paste,Da-jiang

The traditional fermented food has a long production cycle and the product quality is not uniform.Although the flavor is unique,the open production method cannot guarantee the product hygiene.At present,people are actively exploring new bio-starters to realize the industrial production of traditional fermented foods and improve production efficiency and safety.Leuconostoc mesenteroides FX6 screened from northeast traditional fermented soybean paste showed good characteristics in the preliminary experiment.In order to furtherly explore other important metabolic and probiotic properties of FX6 and understand the effect of FX6 on the flavor quality of da-jiang,this study determined the whole genome sequence of FX6 and compared the physicochemical indicators and microorganisms between naturally fermented da-jiang and da-jiang with fortified Leuconostoc mesenteroides.This study aimed at developing a new starter for da-jiang.Results showed that:The whole genome of Leuconostoc mesenteroides FX6 consisted of a 2 047 924 bp circular chromosome and a 28 760 bp circular plasmid.The genome with a GC content of 37.78% contained 72 t RNA genes and 12 r RNAs.The number of open reading frames was 2064.Its genome contains genes related to probiotic properties,DNA replication,DNA repair,transcription,translation,and sugar metabolism and protein metabolism,so we can predict that FX6 had good viability and flavor synthesis ability.The hydroxyl radical scavenging rates of fermented supernatants and cell-free extraction for FX6 were 56.29% and 55.76%,respectively,and the DPPH free radical scavenging rates were 90.85% and62.71%,respectively.The nitrite degradation rate of Leuconostoc mesenteroides FX6 reached 64.82%.The acid production played a major role in the degradation of nitrite.The bacteria itself,intracellular secretions and extracellular secretions can degrad nitrite to different degrees.The fortified Leuconostoc mesenteroides promoted the accumulation of sugar,fat and protein,reduced the total acid and amino acid nitrogen content,inhibited the appearance of nitrite peak during the fermentation of da-jiang,and significantly improved the umami of da-jiang.The color of da-jiang lightened and the nutritional value of amino acids in da-jiang was improved.A total of 6 bacterial phylum and 8 fungal phylum,146 bacterial genera and 95 fungal genera were identified in 20 da-jiang.The microbial richness and diversity during the fermentation of da-jiang were stable.The effect of fortified Leuconostoc mesenteroides on fungi was greater than that on bacteria.Firmicutes,Proteobacteria,Actinobacteri and Ascomycota were the dominant phylum,Weissella,Ignatzschineria,Corynebacterium₁,Aspergillus and Microascus were the dominant genus in the process of da-jiang fermentation.There was a significant difference in the absolute abundance of one bacterial phylum,4 fungal phylum,45 bacterial genera and 34 fungal genera between the two groups of da-jiang.It was found that the relative abundanceof 14 bacteria and 3 fungi was significantly different between traditionally fermented da-jiang and da-jiang with fortified Leuconostoc mesenteroides.The most difference was the relative abundance of Pediococcus.The fortified Leuconostoc mesenteroides can inhibit the growth of Clostridium in food and improve da-jiang safety.The fortified Leuconostoc mesenteroides grew well in group B da-jiang.Time was the main factor affecting the bacterial community.The fortified Leuconostoc mesenteroides was the main factor affecting the fungal community,and the fermentation time was a second factor.Membrane transport,carbohydrate metabolism,amino acid metabolism,replication and repair,and translation were the top five dominant secondary metabolic pathways in the fermentation of soybean paste.Those relative abundance was not significantly different between the two groups of da-jiang.