Cellulase Production Under Solid-State Fermentation by Ethanolic Zygomycetes Fungi: Application of Response Surface Methodology

Background and Objectives: Cellulase is an important enzyme with multiple applications in industries, including food, laundry, pharmaceutical, textile, pulp, paper and biofuel industries. Solid-state fermentation (SSF) is a method for cellulase production, which includes several advantages, compared to submerged fermentation. In this study, cellulase was produced by three filamentous fungi, i.e., Mucor indicus, M. hiemalis and Rhizopus oryzae, through SSF on wheat brans. Materials and Methods: Effects of cultivation time, temperature, and moisture content of the culture media on cellulase production were investigated using response surface methodology (RSM). Experiments were carried out using an orthogonal central composite design. Based on the analysis of variance, a quadratic model was suggested as a function of the three variables to express cellulase production. The optimum parameters for cellulase production by the fungi were achieved and the highest cellulase activity was reported. Results: The fungi produced significant amounts of cellulase. Models fitted to the experimental activities of the fungi included high regression coefficients. The optimum media temperature for all fungi was 26.6 ºC. For M. indicus and R. oryzae, the optimum moisture content and cultivation time of the media were 71.8% and 33.2 h, respectively. These parameters were respectively reported as 38.18% and 66.81 h for M. hiemalis. The highest cellulase activities by R. oryzae, M. indicus and M. hiemalis were 281, 163 and 188 U per g of dry wheat bran, respectively. The maximum enzyme production was seen in R. oryzae. Conclusions: In conclusion, these three advantageous fungal strains can successfully be used for cellulase production through SSF with relatively high yields, compared to other fungal strains.