Enhancement of 1-deoxynojirimycin content and α-glucosidase inhibitory activity in mulberry leaf using various fermenting microorganisms isolated from Korean traditional fermented food

Abstract

Mulberry leaf is known to be effective in inhibiting increases in blood glucose levels in diabetic patients. 1-Deoxynojirimycin (DNJ), a α-glucosidase inhibitor, is the major effective component in mulberry leaf. The aim of this study was to evaluate the level of DNJ in mulberry leaves fermented by various microorganisms, including lactic acid bacteria, yeast, and the bacillus isolated from Korean traditional fermented soybean food, and to assess the inhibitory effect of fermented mulberry leaf powder extract (FMLE) on α-glucosidase activity. The DNJ content in unfermented mulberry leaf powder extract (UFMLE), the control, was determined to be 53.2 ± 1.5 mg/100 g (dry weight eq.). Lactobacillus plantarum, Zygosaccharomyces rouxii, Wickerhamomyces anomalus, and Bacillus subtilis remarkably increased the DNJ levels in mulberry leaves by 1.2, 1.5, 2.0, and 1.8-fold, respectively, compared to the control. The inhibitory effects of the FMLEs on α-glucosidase were also examined at various concentrations, and their α-glucosidase inhibitory effects tended to be higher than that in UFMLE. These findings suggest that Korean traditional fermenting microorganisms can be used as starter strains for the development of DNJ-enhanced food products, and that FMLEs have the potential to be used in various functional foods for the prevention of diabetes.