Deglycosylation of isoflavone C‐glycosides by newly isolated human intestinal bacteria

BACKGROUND: Plant isoflavones are mostly present in the glycoside form. Isoflavone aglycones produced by intestinal microflora are reported to be more bioactive than the glycoside form. However, the deglycosylation of isoflavone C-glycosides is known to be rare, and is less studied. RESULTS: Three new bacteria were isolated from human faecal samples, two of which hydrolysed the C-glycosidic bond of puerarin, daidzein-8-C-glucoside. They were identified as two Lactococcus species, herein designated as MRG-IFC-1 and MRG-IFC-3, and an Enterococcus species, herein designated MRG-IFC-2, based on their 16S rDNA sequences. From a reactivity study, it was found that Lactococcus sp. MRG-IFC-1 and Enterococcus sp. MRG-IFC-2 hydrolysed isoflavone C- and O-glycosides, as well as the flavone O-glycoside apigetrin, but could not hydrolyse the flavone C-glycosidic bond of vitexin. The other Lactococcus sp., MRG-IF-3, could not hydrolyse the C-glycosidic linkage of puerarin, while it showed a broad substrate spectrum of O-glycosidase activity similar to the other two bacteria. Puerarin was completely converted to daidzein within 100 min by Lactococcus sp. MRG-IFC-1 and Enterococcus sp. MRG-IFC-2, which is the fastest conversion among the reported human intestinal bacteria. CONCLUSION: Two new puerarin-metabolising human intestinal bacteria were isolated and identified, and the deglycosylation activity for various flavonoid glycosides was investigated. The results could facilitate the study of C-glycosidase reaction mechanisms, as well as the pharmacokinetics of bioactive C-glycoside natural products.