16-02: The need to increase the specific surface area of cellulose: how pretreatment and the nature of the “cellulase complex” are critical to obtaining high-yield sugar streams from lignocellulosic substrates when using low enzyme dosages

The resistance of lignocellulosic materials, particularly the cellulosic component, to enzymatic attack is due to nature using physical, mechanical and chemical mechanisms to make it remarkably difficult to actually access the chemical bonds that we in the bioconversion community want to ultimately hydrolyze. It has been shown that, regardless of substantial differences in the source, structure and chemical composition of lignocellulosic feedstocks and the pretreatment technology used to “open up” the substrate, the susceptibility of the cellulose to enzymatic hydrolysis is strongly dependent on the specific surface area (SSA) of the cellulose to the enzymes. An effective pretreatment process should ideally provide good recovery of the lignin, hemicellulose and cellulose in a useable form, be inexpensive and applicable to a wide range on feedstocks, while significantly increasing the SSA. However, various compromises often have to be made to try and meet all of these goals. It is apparent that the “optimum enzyme cocktail” used to hydrolyze the cellulose is significantly influenced by both the nature of the substrate and the pretreatment technology used. By maximizing the synergies between pretreatment and enzymatic hydrolysis it is possible to both minimize the dehydration reactions that decrease carbohydrate recovery while enhancing the SSA of the cellulose so that effective hydrolysis can be achieved at low enzyme dosages. We will discuss how key components in the “cellulase complex” such as accessory enzyme and mechanisms such as amorphogenesis all play a role in increasing cellulose accessibility and allowing the enzymes actually access the β-1,4 bond.