Microwave Pretreatment of Substrates for Cellulase Production by Solid-State Fermentation

The agricultural residues, wheat bran and rice hulls, were used as substrates for cellulase production with Trichoderma sp 3.2942 by solid-state fermentation. Microwave irradiation was employed to pretreat the substrates in order to increase the susceptibility. Although the highest cellulase yield was obtained by the substrates pretreated by 450 W microwave for 3 min, pretreatment time and microwave power had no significant effect on cellulase production. The initial reducing sugar content (RSC) of substrates was decreased by microwave irradiation, but more reducing sugars were produced in later fermentation. Alkali pretreatment combined with microwave pretreatment (APCMP) of rice hulls could significantly increase cellulase yields and reducing sugar. The maximum filter paper activity, carboximethylcellulase (CMC)ase, and RSC were increased by 35.2%, 21.4%, and 13%, respectively, compared with those of untreated rice hulls. The fermented residues could produce more cellulase and reducing sugars than fresh rice hulls after they were treated by APCMP. The increased accessibility of the substrates by microwave pretreatment was mainly achieved by rupture of the rigid structure of rice hulls. However, for alkali pretreatment and APCMP, delignification and removal of ash played very important roles for increasing the acceptability of substrates.