Production of biomass-degrading enzymes by Trichoderma reesei using liquid hot water-pretreated corncob in different conditions of oxygen transfer

Abstract

Enzymatic hydrolysis accounts for 20% of the total cost in the conversion process of lignocellulosic biomass into bioethanol. Therefore, production of biomass-degrading enzymes by using lignocellulosic residue as a fermentation substrate may be an alternative to decrease the production costs. In this study, corncob (CC) has been pretreated by liquid hot water (LHW) at 200 °C for 30 min and used as inducer source for production of biomass-degrading enzymes by Trichoderma reesei MUM 97.53. The pretreatment was used to increase the cellulose content and the accessibility to lignocellulosic material. Although the filamentous fungus secreted a broad range of cellulolytic and hemicellulolytic enzymes when grown on untreated CC, higher enzyme productions were obtained when cultured on LHW-pretreated CC in a 2-L stirred tank bioreactor (STB). Besides, the effects of aeration (2 and 4 vvm) and agitation (150 and 250 rpm) rates on enzyme production were studied by submerged fermentation in a batch STB and correlated with the volumetric oxygen transfer coefficient (kLa). Maximal cellulase, xylanase, and -xylosidase productions were found at 150 rpm and 4 vvm, while the highest -glucosidase levels were obtained at 150 rpm and 2 vvm, that corresponded to kLa values of 32.50 h1 and 16.41 h1, respectively. At higher agitation, a lower enzymatic production was observed probably due to the high shear stress in the fungal hyphae.