Three-phasic fermentation systems for enzyme production with sugarcane bagasse in stirred tank bioreactors: Effects of operational variables and cultivation method

Abstract

The high cost of enzymes is one of the main bottlenecks affecting the industrial production of cellulosic ethanol, which therefore requires the development of improved bioprocesses for the manufacture of cellulases. The present work concerns the selection of operating parameters for enzyme production in three-phasic bioreactors, using sugarcane bagasse as substrate. The parameters considered included cultivation method, substrate particle size and pretreatment, agitation speed, and pH. For both shake flask and stirred tank bioreactor (STB), a new sequential cultivation method employing steam explosion pretreated sugarcane bagasse significantly improved enzyme production, compared to conventional submerged fermentation. Larger substrate particle size provided a better support for fungal growth in shake flasks, while smaller particles resulted in greater homogeneity in stirred tank bioreactors. Maximum endoglucanase and xylanase production in the STB were 1599±66 and 4212±133IUL−1, respectively, under sequential cultivation using pretreated bagasse particles smaller than 0.5mm, agitation speed of 700rpm, and pH 5.0. The findings provide useful information concerning the influence of operational variables on (hemi) cellulases production in STB three-phasic cultivations, which should contribute to the development of bioprocesses using lignocellulosic materials in large-scale bioreactors.