| Sour bamboo shoots as a kind of southern special flavor food,are made by natural fermentation using fresh bamboo shoots as raw materials.At present,there are not many studies on fermented sour bamboo shoots,mainly focusing on nutrients and flavor substances.There are few studies on the diversity of microorganisms and their metabolic products during different fermentation stages.In this study,fresh bamboo shoots were used as raw materials,salt-free fermentation was adopted,16 S r DNA high-throughput sequencing technology,UHPLC-Q-TOF-MS,and HPLC and HS-SPME-GC-MS are used to study the changes of microbial diversity,metabolite and flavor substances during the fermentation of sour bamboo shoots.The research results are as follows:(1)Taking the bamboo shoots fermented for 30 days,60 days,90 days,120 days,and 150 days as the research object,the bacterial flora structure and diversity of the acid shoots under different fermentation time conditions were studied.The results of the study found that the bacterial community was rich during the fermentation of sour bamboo shoots.During the fermentation process,the types and numbers of bacteria changed continuously with the environmental changes caused by continuous fermentation.At the phylum level,Firmicutes is dominant,with a relative abundance of 93.73%?99.57%,followed by Proteobacteria and Actinobacteria,with a relative abundance of 0.41%?6.11% and 0.02%?0.14%.Species annotation results at the class and order levels show that the relative abundance of Bacilli and Lactobacillales is up to 93.52%?99.52%.At the family level,the relative abundance of Lactobacillaceae is up to 78.67%?94.89%.The result of species annotation at the subordinate level shows that the dominant bacteria of the five groups of samples are all Lactobacillus,and their relative abundance is 86.06%-95%.In the fermentation process,the relative abundance of Lactobacillus increases and decreases first and then decreases with the extension of fermentation time.The relative abundance is as high as 95.27% when fermented to 90d;Lactococcus increases with the fermentation time.The relative abundance gradually decreased;the relative abundance of Weissella decreased with the extension of fermentation time.(2)During the fermentation of acid bamboo shoots from 0 to 150 days,the total acid content showed an upward trend from 0 to 120 days of fermentation,and tended to be stable after 120 days,with the content up to 11.05k/kg;the content of amino acid nitrogen,The content of total sugar showed a downward trend with the extension of fermentation time,and the content was the highest at 0d of fermentation,the contents were as high as 0.23g/100 g and 2.54mg/g respectively;the content of flavonoids increased first and then decreased with the extension of fermentation time.The content reached 3.56mg/g at 120 d after fermentation.Detection of lactic acid,acetic acid,oxalic acid,citric acid,malic acid,and tartaric acid during the fermentation of sour bamboo shoots.Lactic acid and acetic acid are the main organic acids that contribute to the sour taste.Citric acid and tartaric acid have a weak contribution to the sour taste;The content of the six organic acids in all of them showed an increasing trend,but the growth rate was different.The relative content of lactic acid was as high as 3.71±0.03mg/g when fermented for 150 days;the content of acetic acid was next,and the relative content reached 3.07±0.01mg/g.when fermented for 150 days.(3)The qualitative analysis of volatile components during the fermentation process of sour bamboo shoots from 0-150 days found that the relatively active flavor substances in the fermentation process were mostly esters,phenols and acids.Alcohol content showed a trend of increasing first and then decreasing,the content was as high as 13.94% at 30 days;ester content had been decreasing,and the content was as high as 27.24?g/g at 0 days;phenol content increased first and then decreased The trend is that the content is up to 64.89?g/g at 90 days of fermentation;the acid content increases first and then decreases,and the content is up to 25.86?g/g at 120 days of fermentation.P-cresol is the most abundant flavor substance in the whole fermentation process.Its relative content is as high as 55.4±0.01?g/g at 90 days of fermentation,with a pungent odor.The threshold value of p-cresol is only 0.002mg/kg,which has a high OAV value,so it has a significant impact on the formation of sour bamboo flavor.(4)Establish an efficient and rapid high performance liquid chromatographymass spectrometry analysis method to determine the amount of metabolites in three fermentation time periods(30d,90 d,150d)during the fermentation process of sour bamboo shoots,and apply principal component analysis,yi9 partial least squaresand other metabolomic data analysis methods to screen for significant differences in metabolites between the three periods of sour bamboo shoot fermentation(fermented bamboo shoots 30 d and 90 d,fermented 30 d and 30d)150d sour shoots,fermented90 d and 150 d sour shoots).The results show that under the positive and negative ion monitoring modes,72 significant differential metabolites were found in the three periods,mainly including organic acids such as L-3-phenyl lactic acid and orotic acid,and amino acids such as lysine and aspartic acid,1-Methyladenosine and other nucleoside compounds.The number of organic acids,amino acids and nucleoside compounds in the three periods of sour bamboo shoots showed a trend of first increasing and then decreasing.A total of 22 metabolic pathways were enriched during the fermentation process,of which the most critical metabolic pathways are amino acid metabolism,carbohydrate metabolism,lipid metabolism and nucleotide metabolism.The change multiples of metabolites expressed in 90 d and 150 d fermented bamboo shoots were small,indicating that 90 days was the best period for the enrichment of fermented sour bamboo shoots. |
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