Cellulases: Agents for fiber modification or bioconversion? The effect of substrate accessibility on cellulose enzymatic hydrolyzability

Biodegradation of cellulose to glucose is the principal reaction in any application involving the treatment of natural fibers with cellulase enzymes, e.g., wood fiber modification, biomass conversion or even textile biopolishing. In an attempt to elucidate the impact of cellulose accessible surface area on the hydrolyzability of cellulosic substrates, steam-exploded Douglas-fir wood with and without bleaching as well as Avicel were hydrolyzed using a complete cellulase system. The term "conversion efficiency" (epsilon(t)) was defined as the percentage of original cellulose converted to glucose after t hours per unit of enzyme used, and the effect of enzyme loading on the initial reaction rate and conversion efficiency was investigated. It was shown that enzyme adsorption capacity and lignin content could not accurately predict the hydrolyzability of a substrate, and that disrupting the fiber structure using a pretreatment method, such as steam explosion, could enhance the initial response of the substrate to enzyme loading and help achieve better conversion yields.