Enhancement of 1-deoxynojirimycin content in leaf extracts of Morus alba L. by lactic acid bacteria fermentation

The α-glucosidase inhibitor plays a key role to control postprandial blood glucose levels in diabetic patients with type 2 diabetes and 1-deoxynojirimycin (DNJ) is the main αglucosidase inhibitor in mulberry (Morus alba L.). Mulberry leaf was extracted with 30% ethanol and the extracts were fermented using seven kinds of lactic acid bacteria (LABs) in order to increase the contents of DNJ in the leaf extracts. The DNJ content of Lactobacillus acidophilus among LABs examined in this study was the highest to 21.77 μg/ml and appeared to be about 2.5 times higher than 8.38 μg/ml of non-fermented control. All of the fermented mulberry leaf extracts appeared to enhance a certain degree of α-glucosidase inhibitory activity and the IC₅₀ values against α-glucosidase, compared to the non-fermented extract. Among LABs, L. casei KCTC 3109 (Inhibition = 43.83% ± 0.98%, IC₅₀=290.06 μg/ml) showed more remarkable inhibitory effects than the non-fermented control (30.78%±1.89%, IC₅₀=429.80 μg/ml). Furthermore, dose-dependent inhibition of the extract showed a significant level of inhibitory effects within only the range of 1 mg/ml concentration. The results suggest that the fermentation method with LABs can enhance the increase of the contents of hypoglycemic constituents such as DNJ on ethanol extracts of mulberry leaves.