Improving the hypoglycemic activity of phenolic extracts from Dendrobium officinale leaves using the solid-state fermentation of edible fungi

Fermentation is a technique commonly used to improve the health of agricultural products. In this study, Dendrobium officinale leaves were solid-state fermented by edible fungi, and the results showed that Aspergillus oryzae was the suitable strain to increase their inhibition abilities against α-glucosidase and α-amylase by 9.05- and 2.99-times, respectively. Chemical analysis showed that the contents of total phenolics, free phenolics, bound phenolics, quercetin, and rhoifolin were increased by 2.54-, 3.41-, 2.09-, 6.03-, and 8.06-times, while those of luteolin, gallic acid, and kaempferol were increased from undetectable level to 0.45, 46.99, and 4.47 μg/g, respectively, after four days of fermentation by A. oryzae . Furthermore, the hypoglycemic activity of D. officinale leaves was tested in vivo . The fermented group showed higher capacity for decreasing fasting blood glucose levels and insulin resistance, reversing dyslipidemia, ameliorating oxidative stress, and reversing pancreatic and liver lesions in db/db mice. These findings suggest that it is effective to utilize and valorize D. officinale leaves as functional food or food additives through the fermentation by A. oryzae .