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Tartary buckwheat ( Fagopyrum tataricum ) is a rich dietary source of flavonoid glycosides, which can be enzymatically converted to ethyl rutinoside (ER) by the endogenous rutin-hydrolysing enzyme (RHE) in tartary buckwheat. However, owing to the lack of commercially available RHE, its optimal catalytic conditions and substrate specificity have not been systematically characterised. Herein, food-grade RHE was successfully isolated from tartary buckwheat, and optimal conditions for ER production were established. The highest catalytic efficiency was achieved at pH 5.0, 40°C and 20% ethanol, with a substrate-to-enzyme ratio of <6. Substrate specificity assays revealed that RHE preferentially hydrolysed 3-O-rutinoside flavonoids, including rutin, kaempferol rutinoside, cyanidin rutinoside and delphinidin rutinoside, as indicated by their high catalytic efficiency constant. Molecular docking validated the favourable binding affinity of RHE for these substrates. When added to extracts from various tartary buckwheat tissues, RHE efficiently catalysed ER formation. These findings provide a theoretical foundation for targeted ER production and highlight the potential of RHE as a promising biocatalyst for modifying flavonoid glycosides in functional food development. • Plant-derived RHE was purified and used for ER biosynthesis. • 3-O-rutinoside flavonoids serve as suitable substrates for ER biosynthesis. • Tartary buckwheat flowers contain the highest level of 3-O-rutinoside flavonoids.
Xiao et al. (Wed,) studied this question.