Validation of experimental model
The optimum values of determined variables were obtained by solving the regression equation (Eq. (2)). The optimal conditions of culture media for CMCase production estimated by the model equation were X1 = 12.39 g/L, X2 = 0.48 g/L, and X5 = 6.12 g/L. The theoretical CMCase activity predicted under the above conditions was 1.207 Unit/ml. In order to verify the prediction of the model, the optimal conditions were applied to three independent replicates for CMCase production. The average CMCase activity was observed to be 1.180 ± 0.14 Unit/ml. This verification revealed that the model has a high degree of accuracy of more than 98%. Also, observed CMCase activity which was produced in optimal media was found to be 1.61 fold higher than that in the original medium (0.733 Unit/ml). This value was well fit within the estimated value of the model equation. Thus, this result demonstrates that response surface methodology with appropriate experimental design can be effectively applied to the optimization of the factor of culture media in microbial fermentation. Mainly, this study focused on the application of response surface methodology to optimize the culture media for cellulase production by P. brasilianum KUEB15. This could provide useful information for the development of the economic and efficient production of microbial enzymes.
Conclusion
Various lignocellulosic biomass was used as a carbon source of the fermentation medium for cellulase production. Corn stover, which showed the highest activity of CMCase (0.731 Unit/ml), was determined as a suitable carbon source. The important variables of culture media for CMCase production were investigated by Plackett-Burman design. From the result, the three significant variables (corn stover, urea and ammonium sulfate) were determined for CMCase production and investigated on CCRD. The variables were determined for the effects of five-level-three-factors and their interactions on cellulase production. The results obtained from ANOVA indicated that the determination of coefficient (R2) was calculated as 0.918 for CMCase activity. The maximal production was accomplished by a high concentration of ammonium sulfate and a low concentration of urea with a moderate concentration of corn stover. In this investigation, we confirmed that the CMCase production was strongly inhibited by more than 2 g/L of urea concentration. The optimal conditions of culture media for CMCase production estimated by the model equation were 12.39 g/L corn stover, 0.48 g/L urea and 6.12 g/L ammonium sulfate. The predicted CMCase activity by the model was 1.207 Unit/ml, and the observed CMCase activity which was produced in optimal media was 1.180 Unit/ml. This verification revealed that the model has a high degree of accuracy more than 98%, which was well fitted within the estimated value of the model equation. Thus, this study demonstrated that RSM, with appropriate experimental design can be effectively applied for the optimization of the variables of culture media in microbial fermentation.