Purification and fermentation characteristics of exopolysaccharide from Fomitopsis castaneus Imaz

Short-chain fatty acids (SCFAs), which are the end products of carbohydrate fermentation in the gut, mainly contribute to energy metabolism in mammals. The amount of SCFAs produced during fermentation is an important parameter that characterizes the fermentation capacity of a system. This paper reports on the fermentation characteristics of exopolysaccharides (EPS) isolated from Fomitopsis castaneus Imaz, a wood-rot fungal species. We isolated and purified the main EPS fraction by freeze drying and DEAE-Sepharose fast flow chromatography. We then analyzed the monosaccharide composition of EPS. The isolated EPS was mainly composed of glucose, galactose, rhamnose, mannose, and arabinose. The characteristic absorption peaks of sugar esters were also detected. Fresh fecal extracts from healthy adults and children were used as fermentation substrate to simulate the human intestinal environment (anaerobic conditions at 37 °C) and study the fermentation characteristics of the purified EPS. Adding the isolated EPS to the fermentation system of the simulated intestinal environment increased the SCFAs content in the fecal extract of adults and children. However, the yield of SCFAs, particularly butyric acid, in the fermentation system of fecal extract in children was higher than that in adults. Furthermore, adding exogenous lactic acid bacteria, such as Enterococcus fecalis and Enterococcus fecium, to the fermentation system effectively increased the SCFAs concentration in the model intestinal system of the children. By contrast, adding E. fecalis, Lactobacillus rhamnosus, and E. fecium increased the content of the produced SCFAs in the system of adults. Those results indicate that EPS isolated from F. castaneus Imaz was effectively fermented in the simulated intestinal environments, and the fermentation capability was enhanced by adding microbial flora.