Antioxidant capacity and α-glucosidase inhibitory activity of leaf extracts from ten ramie cultivars

Ramie (Boehmeria nivea L. Gaud) is widely cultivated as a raw material for producing natural textiles due to its fine and strong fibers. Ramie leaves are by-products and rich in bioactive compounds that contribute to the medicinal properties of its extracts. This study was conducted to identify the phenolic compounds and evaluate the antioxidant capacity and α-glucosidase inhibitory activities of ramie leaves extracts, obtained from ten cultivars widely growing in China. The phenolic compounds were identified using advanced analytical techniques such as ultra-high performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOF-MS) and quantified by UPLC-DAD analysis. The antioxidant activity and α-glucosidase inhibitory properties were evaluated using rapid in vitro assays. The content of total phenolic compounds ranged from 0.52 to 2.41 mg/g DW, and the content of total flavonoids varied from 0.40 to 2.50 mg/g DW. UPLC-ESI-QTOF-MS analysis enabled to tentatively identify 15 compounds in ten cultivars, mainly chlorogenic acid, rutin, p-coumaroylmalic acid, caffeoylmalic acid, feruloylquinic acid, hyperoside and isoquercetin. The highest contents of chlorogenic acid, rutin and p-coumaroylmalic acid were found in cultivar Luzhuqing (LZQ) with 439.49 μg/g DW, 339.97 μg/g DW and 345.93 μg/g DW, respectively. All cultivars performed differently on the antioxidant capacity and α-glucosidase inhibitory ability. Principle component analysis revealed that Qianjiangxianma (QJX) and Luzhuqing (LZQ) were the top two cultivars. This study indicates that ramie leaves can be considered as potentially new source of antioxidants and antidiabetic agents, and it gives insights into cultivar selection in the ramie planting and production.