The Correlation between 1-deoxynojirimycin Content and alpha-glucosidase Inhibitory Activity in the Bark Ethanol Extract from Ramulus mori

Deoxynojirimycin (DNJ) is a novel well known α-glucosidase inhibitor. We studied the relationships between α-glucosidase inhibitory activity and DNJ content in a bark ethanol extract (BEE) from Ramulus mori. Twenty cultivars of Ramulus mori, a shrub also known as mulberry branch, were used as experimental materials. Aqueous alcohol extraction methods were employed to obtain an ethanol extract from the branch bark powder. In vitro bioactivity assay indicated the 20 types of extracted BEE from mulberry branch had strong α-glucosidase inhibitory activity, with an IC50 value ranging from 3.89 to 22.91 μg/mL. The BEE IC50 values from the XiaoJiGuan and BaiGeLu cultivars were the highest and the lowest, respectively. The DNJ content in these extracts were measured using HPLC after DNJ derivation. The results showed these BEEs varied widely. The cultivar QingSang had the highest DNJ content while HuSang 32 had the lowest. Comparative analysis revealed no obvious correlation between 1-deoxynojirimycin (DNJ) content and α-glucosidase inhibitory activity of the BEEs (R=0.0085). These results indicate, aside from DNJ, other unexamined concerned constituents of the BEE from mulberry branch cultivars have significant α-glucosidase inhibitory activity.