S27: Solid State Fermentation of Soybean Hulls for Cellulolytic Enzyme Production: Physico-chemical Characteristics of Substrate and Bioreactor Design

Solid state fermentation (SSF) is an effective means of producing cellulolytic enzyme system for biomass hydrolysis for biofuels and chemicals. Due to the particulate nature of the solid state fermentation physico-chemical characteristics of substrate can significantly influence the biology of enzyme production. By the same token, absence of free water and mixing in SSF the studies on scale-up of the process are important for commercial feasibility. Crystallinity, bed porosity and volumetric surface area of treated (acid/alkali and steam) and untreated soybean hulls were investigated. It was explicitly demonstrated that crystallinity and porosity significantly increased all the enzyme activities, except xylanase, of the system in T. reesei. Total cellulase of 4 FPU/g-ds, and endocellulase of 45 IU/g-ds were obtained in treated hulls with higher crystallinity and porosity compared to 0.75 FPU/g-ds and 7.29 IU/g-ds (endocellulase) in untreated hulls with reduced crystallinity and porosity. The cellulosic composition was fairly same between treated and untreated substrates. In A. oryzae both crystallinity and porosity exclusively enhanced endocellulase levels and significantly decreased xylanase levels.  It was revealed that by modifying the physical characteristics of substrate it was possible to direct enzyme synthesis toward one set of enzymes over others. A novel design of bioreactor has been developed for effective aeration to minimize temperature gradients thereby maintaining optimal enzyme production. This will be discussed during presentation. It is our consent that topics dealt in present study featuring both micro- and macro-scale aspects of SSF would be a step forward in successful commercialization of this ancient technology.