| The imbalance of redox state caused by additional reactive oxygen species is closely related to many diseases.Therefore,it is necessary for people to consume antioxidants through food.The safety of some synthetic antioxidants has been questioned.Therefore,exploring natural and safe antioxidants from biological sources is worth exploring.Tea has good antioxidant activity,and fermented sour tea has better antioxidant activity than other types of tea.However,the composition of the microbial community and the source of antioxidant capacity of sour tea during fermentation remain to be discussed.This study revealed the composition and differences of microbial communities under different fermentation times by sampling fermented sour tea and analyzing16 Sr RNA gene sequences.By detecting the metabolism of antioxidant substances such as catechins in sour tea,the antioxidant capacity of 24 strains of Lactobacillus plantarum isolated from sour tea and sour tea was tested.Conduct metabolomic analysis of sour tea to understand the antioxidant metabolites associated with Lactobacillus plantarum during the fermentation process of sour tea.Then,transcriptome analysis was used to identify the differential genes related to Lactobacillus plantarum during the fermentation process,and combined with metabolomic results,the main metabolic pathways during the fermentation process of sour tea were identified.The results showed that after fermentation,lactic acid bacteria occupied the dominant position in the composition of its microbial community,and the proportion of lactic acid bacteria was the highest.Through further analysis,it was determined to be Lactobacillus plantarum.In sour tea,Enterobacteriaceae dominates at the beginning of fermentation,but its proportion gradually decreases(83-25%)as fermentation proceeds,in inverse proportion to Lactobacillus.Further analysis of the Enterobacteriaceae confirmed that most of them were Klebsiellavariicola.As the fermentation progresses,the antioxidant capacity of sour tea increases,but during post fermentation(the third month of fermentation),the antioxidant capacity decreases due to changes in the fermentation environment.This indicates that there is still much room for improvement in traditional fermentation methods.The optimal time for fermentation of sour tea remains to be studied.The 24 strains of Lactobacillus plantarum isolated from sour tea have good scavenging rates for 1,1-diphenyl-2-trinitrophenylhydrazine free radicals,but they do not have good hydroxyl radical scavenging rates and superoxide anion scavenging rates.Metabolomic and transcriptome analyses suggest that Lactobacillus plantarum may affect the antioxidant capacity of sour tea by influencing the metabolism of nicotinic acid and nicotinamide,as well as the metabolism of glycine,serine,and threonine,leading to an increase in the content of nicotinic acid,cucurbitine,and betaine.Phenolic acids such as coumarin acid and protocatechuic acid also significantly increased during fermentation,and the increase in the production of these phenolic acids is also closely related to Lactobacillus plantarum.At the same time,pyruvate metabolism is enriched with a large number of differential genes,and the metabolism of nicotinic acid and nicotinamide and glycine,serine,and threonine indirectly affect pyruvate metabolism,which may also be one of the reasons why Lactobacillus plantarum affects the antioxidant capacity of sour tea.Through this experiment,it is clear that the second strain of sour tea fermentation is Lactobacillus plantarum,which further explores the mechanism of Lactobacillus plantarum affecting the antioxidant activity of sour tea.It provides a prerequisite for the standardized production of sour tea and provides publicity for China’s intangible cultural heritage.It provides a solid foundation for the development of the antioxidant capacity of Lactobacillus plantarum and its industrial application in fermenting plant based foods to produce high value-added health products. |
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