Antioxidant, antimicrobial activity and inhibition of α-glucosidase activity by Betula alnoides Buch. bark extract and their relationship with polyphenolic compounds concentration.

Betula alnoides has been widely used in local traditional medicinal treatment for a variety of diseases, wounds and to cure diabetes. The air-dried, powdered (200 g) bark was extracted with 80% methanol at room temperature. The combined 80% methanolic extract was partitioned with organic solvents to yield n-hexane, ethyl acetate (EtOAc), n-butanol (BuOH; water saturated), and aqueous fractions for the investigation of antioxidant and antimicrobiology and α-glucosidase activity effects (GAE) of B. alnoides. Antioxidant activity was studied by using antioxidant tests, including electron donation ability test, reducing power, and metal-chelating activity assay. Antioxidant, antimicrobial activity and α-glucosidase inhibitory effect of 80% methanolic extracts and fractions derived from the bark of B. alnoides were evaluated and determined. The results showed that 80% methanolic extracts exhibited high 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity (80.68%). In addition, both the 80% methanolic extract and EtOAc fraction exhibited more potent reducing activity than did butylated hydroxyanisole (BHA) and trolox. The aqueous fraction had higher metal-chelating activity than other fractions. The EtOAc fraction had the highest phenolic and flavonoid content (217.73 ± 1.02 mg GAE/g extract, and 38.42 ± 1.87 mg QE/g extract, respectively). The 80% methanolic extract and EtOAc fraction showed higher levels of antimicrobial activity than did other fractions. The 80% methanolic extract had the most powerful α-glucosidase inhibitory effect (98.46%) at a concentration of 40 µg/mL. The results suggest that bark extracts of B. alnoides could be a potential source of natural antioxidants and for treating pathogenic diseases.