Stability Of Fermentation System Of Traditional Low-salt Paocai And The Effect Of Spices On Fermentation System

Traditional naturally fermented Paocai is usually processed with medium and high salt.Although presence of elevated salt can inhibit the growth of harmful microorganisms,the fermentation cycle is long and high levels of salt have negative effects on human health and the environment.Low-salt fermentation is increasingly desirable with shorter fermentation duration and benefits to human helath.However,a technical challenge to low-salt Paocai fermentation is the difficulties in inhibiting the growth of undesirable bacteria,resulting in unstable fermentation system and inconsistencies in the quality of fermented Paocai products,which seriously restricts the development of traditional low-salt Paocai industry in our country.Spices can improve food flavor and inhibit the growth of certain bacterial populations;therefore are widely used in food fermentation.However,the effects of spices on the fermentation of Paocai,particularly low-salt Paocai,are still unclear.Therefore,to determine the potential benefits of spices in the fermentation of low-salt Paocai,this study investigated the fermentation of low-salt Paocai without added spices(WFL)as compared with that of low-salt Paocai with added spices(YFL),focusing on the microbial communities involved in fermentation using high-throughput sequencing technology.The aim of this study was to understand the effect of microbial community succession on fermentation system stability of traditional low-salt Paocai,which will support the standardization of low-salt production of traditional Paocai.The main results of this study are as follows:(1)The fermentation system of WFL is extremely unstable,and there were obvious differences in physical and chemical indicators and bacterial structure between samples from the same batch.The abundance of Lactococcus,Enterobacteriaceae,Leuconostoc,Massilia,Castellaniella,Lactobacillus,Aeromonas,Faecalibacterium,Blautia and Bacteroides was highly variable in the fermentation system.Leuconostoc was identified as the population with low acidproducing ability while bacterial populations with high acid-producing ability characteristics included Tumebacillus,Stenotrophomona,Pseudomonas,Lactobacillus,Lactococcus,Enterobacteriaceae,and Xanthomonas.(2)The fermentation system of YFL was relatively stable,with consistencies in the physicochemical indexes and composition of dominant bacteria.Leuconostoc was dominant in all samples.The low acid-producing ability were represented by Leuconostoc,while high acidproducing populations were contributed from Enterobacteriaceae,Streptococcus varani,Vibrio,Leuconostoc,Pseudomonas,Streptococcus,Pantoea,Burkholderiaceae.(3)Adding spices could reduce the relative abundance of Enterobacteriaceae,Lactococcus,Pseudomonas and Castellaniella,increase the relative abundance of Leuconostoc and Weissella,reduce the abundance difference between Lactobacillus and Enterobacteriaceae,and maintain the dominance of Leuconostoc in the fermentation system.(4)The addition of spices had a significant effect on the metabolic function of the microbial community in low-salt Paocai.Except for amino acid metabolism,carbohydrate metabolism,cellular community – prokaryotes,membrane transport,and global and overview maps,the abundance of other secondary metabolic pathways was significantly different in WFL and YFL.(5)Phylogenetic analysis showed that most of the microbial biomarkers in WFL were related to the production of nitrite,consumption of organic acids and carbohydrates,while YFL was characterized with the dominance of Leuconostoc,which can be used as a potential starter culture for Paocai.The correlation between microbial biomarkers and physical and chemical indicators further confirmed the results of phylogenetic analysis.(6)The microbial biomarkers identified as Enterobacteriaceae in WFL showed significant positive correlation with amino acid metabolism,chemical structure transformation maps,lipid metabolism,xenobiotics biodegradation and metabolism.The microbial biomarkers identified as Leuconostoc in YFL showed significant positive correlation with the biosynthesis of other secondary metabolites,metabolism of cofactors and microbial,and nucleotide metabolism.