| Broad bean paste is a traditional Chinese condiment,in which hazard nitrogen metabolites,such as biogenic amines,have become increasingly prominent,due to the rich nitrogen source in the fermentation system.Meanwhile,the research on microbial diversity and its effect on biogenic amines metabolite in the industrial fermentation of broad bean paste is relatively lacking.Based on this,the formation law of biogenic amines in the industrial fermentation of broad bean paste paste and the factors affecting its formation were firstly determined.Secondly,the microbial diversity in the industrial fermentation of broad bean paste was analyzed and its correlation with biogenic amines was explored.Finally,the biogenic amines-degrading strains were screened and the effects of biogenic amine-degrading strains on biogenic amines and microorganisms during the fermentation of broad bean paste were investigated.The specific research contents and conclusions are as follows:?1?The content of biogenic amines during the industrial fermentation of broad bean paste was detected by HPLC.The results showed that the main biogenic amines in the fermentation of broad bean paste were putrescine,spermidine and spermine.Putrescine was 50.67 mg·kg-11 in the initial stage,rapidly rose to a maximum value of 134.96 mg·kg-11 after making koji,and then gradually decreased to 26.42 mg·kg-11 with fermentation.Spermidine and spermidine were present in the original stage,and decreased to less than 5 mg·kg-11 after the end of making koji,and then gradually increased to about 20 mg·kg-1.Through the Person correlation analysis of physical-chemical parameters,amino acids and the content of various biogenic amines,it was found that environmental factors presented a certain significant correlation with the content of some biogenic amines;arginine had a certain negative correlation with putrescine,and was significantly positive correlation with spermine;and putrescine and spermidine showed significant negative correlation.?2?High-throughput sequencing was used to detect the contents of biogenic amines of broad bean paste,and the results showed that the relative abundance of Firmicutes accounted for more than 80%of the bacteria in the whole fermentation.In the initial stage,Staphylococcus?19.27%?,Lactococcus?11.88%?,Leuconostoc?9.74%?,Lactobacillus?17.81%?and Weissella?15.26%?were the dominant bacteria.At the end of koji-making,Bacillus?17.81%?and Streptococcus?12.88%?were found.After fermentation with brine,the relative abundance of Streptococcus and Lactococcus increased gradually with the relative decrease of Staphylococcus.The relative abundance of Streptococcus and Lactococcus reached a peak on the 14-20th day.And then Staphylococcus increased sharply on the 26th day.Ascomycetes are the main phylum of fungal microorganisms.While Aspergillus is the most important fungal genus in the whole fermentation process at the level of genus,which the relative abundance is 63.48%-99.98%.In the initial stage,there also were candida,Fusarium,Epicoccum and some unclassified genera in addition to Aspergillus with a relative abundance of 63.48%.With the fermentation with brine,zygomyces appeared on the 14th day,and the relative abundance reached 27.19%at the end of fermentation.At the same time,the results of principal component analysis?PCA?showed that the total biogenic amine and putresine may be related to Bacillus,Lactobacillus,Weissella and Cronobacter,especially there was a close relationship with Bacillus.While spermidine and tryptamine may be associated with Lactococcus and Pantoea,and spermine has a certain correlation with Aspergills,Leuconostoc and Staphylococcu.?3?Through high-throughput screening of biogenic amines-degrading strains,two strains with good biogenic amines degradation effects were obtained.The strain of 1-G6 was Bacillus Amyloliquefaciens,which showed a degradation effect on putrescine?34.92%?,cadaverine?24.04%?,histamine?12.8%?and spermidine?43.27%?.While Bacillus licheniformis?2-B3?had a degradation effect on phenethylamine?13.64%?,putrescine?12.78%?,histamine?19.42%?and spermine?8.68%?.At the same time,the degradation characteristics of the two biogenic amines-degrading strains were tested.Then it was found that strains 1-G6 and 2-B3 had the highest degradation rate when pH was 6,temperature was 35-40?and NaCl concentration was 0-6%.Finally,two strains were applied in the fermentation of broad bean paste to explore the influence of biogenic amines-degrading strains on the fermentation of broad bean paste.In the whole fermentation process,the total biogenic amines content of the fermented broad bean paste added with 1-G6 was lower than the control group at 10-30 mg·kg-1,with a degradation rate of about 20%.While the strain of 2-B3 was added,the total biogenic amine content decreased by 6-24 mg·kg-1,and the degradation rate was about 10%.At the same time,we found that the relative abundance of Bacillus genus was 20.66%-41.42%,which had a significant improvement compared the control group with the relative abundance of 12.52%-23.36%in the whole fermentation process.According to the analysis of Spearman's rank correlation,the inhibitory effect of Bacillus on bacterial genera such as Staphylococcus and Lactobacillus in the experimental group inoculated with biogenic amine-degrading strains was significantly higher than that in the control group.But it had almost no effect on the fungal diversity and the content of physichochemical parameters during the fermentation of bean paste. |
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