Abstract:The fermentation process of the water extract of Cirsium setosum was optimized for improving the flavor and the molecular mechanism of fermentation in improving the flavor was analyzed. The fermentation was carried out with single and mixed strains，and response surface methodology was employed to optimize the fermentation process. Metabolomics was employed to elucidate the molecular mechanism of fermentation in improving the flavor of the water extract of C. setosum. The results showed that Lactobacillus acidophilus mixed with Streptococcus thermophilus in a volume ratio of 3∶1 was the optimal fermentation combination.The optimal fermentation process was as follows：inoculation amount of 1.46%，fermentation temperature of 23.65 ℃，and sucrose content of 4.35%. After fermentation，the content of total flavonoids in the water extract of C. setosum did not show obvious variation.The results of metabolomics analysis showed that after fermentation，sweet components such as 6′-sialyllactose and α-lactose，as well as aromatic components such as 2-hydroxycinnamic acid and bishydroxycoumarin，were significantly increased in the water extract of C. setosum. Meanwhile，bitter substances such as picrotoxinin and sennoside C were significantly decreased. The metabolites related to flavor improvement were mainly enriched in the metabolic pathways of sugars，amino acids，and nucleotides.