Optimization of fermentation process for the production of intracellular polysaccharide from Paecilomyces cicadae and the immuno-stimulating activity of intracellular polysaccharide.

Optimization of fermentation process for the production of intracellular polysaccharide (IPS) from the fungus Paecilomyces cicadae and the immuno-stimulating activity of IPS were carried out. The quantitative effects of initial pH, fermentation temperature and time on the yield of IPS content produced by P. cicadae in submerged fermentation were investigated separately using response surface methodology (RSM). The three factors chosen for the present investigation were based on the results of a previous Plackett-Burman (PB) design. The experimental data obtained were fitted to a second-order polynomial equation using multiple regression analysis and also analyzed by appropriate statistical methods. RSM analysis showed good correspondence between experimental and predicted values. It was found that three parameters represented significant effect. Probability value (p < 0.0001) demonstrated a very high significance for the regression model. By solving the regression equation and analyzing the response surface contour plots, the optimal process parameters were determined, i.e. fermentation temperature 24.53 °C, initial pH 7.46 and fermentation time 73.9 h. The maximum predicted yield of IPS was 356.02 μg/ml under the optimal conditions. Meanwhile, IPS from P. cicadae was found to have direct immuno-stimulating activity in vitro on murine macrophage RAW264.7 proliferative response and to stimulate nitric oxide generation in a dose-dependent manner.