Optimization Of Submerged Culture Conditions For The Production Of Exopolysaccharide By Pleurotus Nebrodensis And Analysis Of The Components Of The Polysaccharide

Pleurotus nebrodensis is a precious and valuable edible and medicinal mushroom. It belongs to Eumycota, Basidiomycetes, Agaricales, Pleurotaceae, Pleurotus.This nutritional and functional mushroom tastes crisp and delicious with pleasant full-bodied aroma. Besides rich in protein, polysaccharide and fatty acid, it also contains a large number of vitamin, edible fibre and many kinds of mineral elements, for instance, calcium, iron, zinc, manganese and so on. A number of present-day pharmacologic studies have shown that polysaccharide of Pleurotus nebrodensis has immuno-enhancing function, antivirus and antitumor effects, and has shown utility in the lowering of cholesterin content and the prevention of arteriosclerosis.The polysaccharides of Pleurotus nebrodensis not only exist in its fruiting bodies, but also in the mycelia and fermentation broth obtained from liquid culture. Liquid cultures have a lot of advantages, especially for mass production, since they allow for the harvesting of mycelia and the relatively easy extraction of useful material from the fermentation broth. The use of liquid cultures also facilitates the release of polysaccharide.The medicinal properties and applications of Pleurotus nebrodensis polysaccharides had been realized and attached importance to all over the world by now. In recent years, more and more researches have turned to focus on the extraction and physiological function of the Pleurotus nebrodensis polysaccharides at home.In this research the nutritional and environmental conditions for producing exopolysaccharides (EPS) from Pleurotus nebrodensis in submerged culture were optimized for the first time. This will pave the road for the commercial production of polysaccharide from Pleurotus nebrodensis in large scale and its further exploitation. It showed that the optimum combination of carbon and nitrogen sources for producing the maximum EPS yield was maltose with yeast extract. And the optimum fermentation medium obtained by orthogonal test contained 200 g l^-1 bran, 25 g l^-1 maltose, 3 g l^-1 yeast extract, 1 g l^-1 KH2PO4, 1 g l^-1 MgSO4 7H2O. By single factor tests, the optimum fermentation conditions were obtained as follows: initial pH 8.0, 25℃of incubation temperature, 160 rpm of revolution speed, 100 mL liquid medium in a 250-mL Erlenmeyer flask, 0.50 cm2 mycelial block of inoculation volume and 4 days of fermentation time. Under the optimum conditions, the biomass of Pleurotus nebrodensis was 4.13 g/L, 2.3 times the control (1.77 g/L); and the content of EPS was 2.40 g/L, 3.6-fold compared to the control (0.664 g/L).In this research we also separate and purify the polysaccharides from the mycelia and the fermentation broth of Pleurotus nebrodensis respectively. By cellulose DE-52 chromatography, we obtained two polysaccharide components from the mycelial polysaccharides and three polysaccharide components from polysaccharides of the fermentation broth. By Sephadex G-100 chromatography, we obtained the sub-component severally from every polysaccharide component.We analyze the constitute of the monosaccharides of Pleurotus nebrodensis polysaccharides for further exploitation. The results are as follows: the sub-components of mycelial polysaccharides mainly contain rhamnose; and the sub-components of polysaccharides from fermentation broth mainly contain arabonose.