Chapter 3 - Solid State Fermentation for Production of Microbial Cellulases

Abstract

Cellulose, present in renewable lignocellulosic material, is considered to be the most abundant organic substrate on earth for production of hexose and pentose sugars, feedstock for fuel, and for other chemicals. Research on cellulase has progressed very rapidly in the past few decades with an emphasis on enzymatic hydrolysis of cellulose to hexose sugars. The enzymatic hydrolysis of cellulose requires the use of cellulase [1,4-(1,3:1,4)-β-D-glucan glucanohydrolase, EC 3.2.1.4], a multiple enzyme system consisting of endo-1,4,-β-D-glucanases [1,4-β-D-glucanases (CMCase, EC 3.2.1.4)], exo-1,4,-β-D-glucanases [1,4-β-D glucan cellobiohydrolase, FPA, EC 3.2.1.91], and β—glucosidase (cellobiase) (β-D-glucoside glucanohydrolase, EC 3.2.1.21). Major impediments to exploit the commercial potential of cellulases are the economic yield, stability, specificity, and above all, the cost of production. In the last few years, emphasis has been devoted mainly to submerged fermentation and less attention has been given to solid state fermentation (SSF). SSF refers to the process whereby microbial growth and product fermentation occur on the surface of solid materials. This process occurs in the absence of “free” water, where the moisture is absorbed to the solid matrix. The direct applicability of the product, the high product concentration, lower production cost, easy product recovery, and reduced energy requirement make SSF a promising technology for cellulase production. This chapter covers the production of cellulase in SSF using various lignocellulosic substrates, the microorganisms involved, cultural conditions, process parameters (ie, moisture content and water activity, mass transfer processes: aeration and nutrients diffusion, substrate particle size, temperature, pH, surfactants, etc.), bioreactor designs, and the strategies to improve enzyme yield.