Abstract: The enhancing effect of Chinese yam fermentation with Cordyceps militaris on its antioxidant activity was studied, and the underlying mechanism was analyzed. Fresh and fermented (with Cordyceps militaris and its metabolites) samples were compared for differences in their antioxidant activity in terms of scavenging of superoxide anion and 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radical. Moreover, fingerprinting analysis by high performance liquid chromatography (HPLC) was conducted as well as scanning electron microscopy (SEM) and Fourier transform infrared spectrometer (FTIR). The result showed that free radical scavenging rates of the fermented sample were significantly higher than the fresh sample (P < 0.05). The contents of total phenol, total flavonoids, total saponins were significantly higher in the former than in the latter (P < 0.05). The fermented sample contained some compounds not found in the fresh one, and there were significant changes in the contents of the six shared compounds between them. The microstructure of Chinese yam could be broken down by Cordyceps militaris. Sugars in Chinese yam such as polysaccharide and cellulose could be metabolized as a carbon source by Cordyceps militaris into phenols and saponins. This study confirmed fermentation with Cordyceps militaris to be effective in enhancing the antioxidant activity of Chinese yam, which may be mainly ascribed to the changes in the types and contents of bioactive components as well as the microstructure.

Key words: Chinese yam; Cordyceps militaris; fermented Chinese yam with Cordyceps militaris and its metabolites; antioxidant activity; enhancement