Abstract
Coarse cereals are rich in flavonoids, which are bioactive substances with a wide range of functions. Biotransformation is considered an emerging approach to methylate flavonoids, displaying prominent regio- and stereoselectivity. In the current study, liquiritigenin, naringenin, and hesperidin flavonoids were biotransformed using O-methyltransferases that were heterologously expressed in Saccharomyces cerevisiae BJ5464-NpgA. Nuclear magnetic resonance (NMR) spectroscopy was used together with high-resolution mass spectroscopy analysis to determine the structures of the resulting methylated transformants, and their antimicrobial and antiproliferation activities were also characterized. Among the five methylated flavonoids obtained, 7-methoxy-liquiritigenin had the strongest inhibitory effect on Candida albicans SC5314 (C. albicans SC5314), Staphylococcus aureus ATCC6538 (S. aureus ATCC6538), and Escherichia coli ATCC25922 (E. coli ATCC25922), which increased 7.65-, 1.49-, and 0.54-fold in comparison to the values of their unmethylated counterparts at 200, 250, and 400 μM, respectively. The results suggest that 3′-methoxyhesperetin showed the best antiproliferative activity against MCF-7 cells with IC50 values of 10.45 ± 0.45 µM, which was an increase of more than 14.35-fold compared to that of hesperetin. These results indicate that methylation enhances the antimicrobial activities and antiproliferative effects of flavonoids. The current study provides an experimental basis for further research on flavonoids as well as flavonoid-containing crops in the development of antimicrobial and anti-breast cancer drugs in addition to supplementary and health foods. The biotransformation method is ideal, as it represents a means for the sustainable production of bioactive flavonoids.
Highlights
Flavonoids are a type of plant secondary metabolite that are widely present in many minor grains, such as Tartary buckwheat, quinoa, and barley [1,2,3]
The current study confirmed that three of the examined flavonoids tended to be transformed by HsOMT and not LtOMT
Five known flavonoids were extracted and isolated from fermented cultures, and their structures were subsequently characterized by Nuclear magnetic resonance (NMR)
Summary
Flavonoids are a type of plant secondary metabolite that are widely present in many minor grains, such as Tartary buckwheat, quinoa, and barley [1,2,3]. In addition to being diverse in variety, flavonoids possess complex structure types, and they perform many bioactive functions, including antioxidation effects [4,5], antiproliferative effects [6], and antibacterial effects [7,8]. Many natural flavonoids present many disadvantages, such as low content, poor water solubility, and unstable bioavailability. Adverse reactions caused by puerarin have been reported in its clinical application, including fever, allergies, and hemolysis [10], which are related to its poor solubility and low bioavailability.
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