Isolation, Identification, and Quantification of Tyrosinase and α-Glucosidase Inhibitors from UVC-Irradiated Mulberry ( Morus alba L.) Leaves

Methanol extracts from ultraviolet (UV) C-irradiated mulberry leaves (UVC-IML) exhibit stronger Tyrosinase and α-glucosidase inhibitory activities than those from unirradiated mulberry leaves. Through a bioassay-guided fractionation and purification process, two oxyresveratrol derivatives, oxyresveratrol (ORT) and 4'-prenyloxyresveratrol (PORT), and six 2-arylbenzofuran derivatives [moracin B (MCB), moracin C (MCC), moracin M (MCM), moracin N (MCN), 6,5'-dimethoxymoracin M (DMMCM), and chalcomoracin (CMC)] were isolated from the methanol extract from UVC-IML. Their chemical structures were determined by UV, mass, and nuclear magnetic resonance spectrometry. ORT and PORT showed potent Tyrosinase inhibitory activities with the half maximal inhibitory concentration (IC₅₀) values of 0.57 and 0.90 μM, respectively, and CMC exhibited significant Tyrosinase and α-glucosidase inhibitory activity with IC₅₀ values of 5.61 and 6.00 μM, respectively. Levels of these eight compounds were increased significantly following irradiation compared with untreated mulberry leaves; ORTs increased approximately 4 fold and moracins increased 2~16 fold. These data suggest that UVC-IML may represent a promising source of nutraceuticals and cosmeceuticals for prevention of diabetes and skin aging.