7-12: The use of pulp and paper and substrate characterization methods to identify the ways of increasing cellulose accessibility (or specific surface area) to enzymatic hydrolysis

The recalcitrance of biomass toward carbohydrate degrading enzymes necessitates the use of a pretreatment step to increase the accessibility of the cellulose to these enzymes. However, it has proven difficult to quantify the amount of cellulose accessible to cellulases (or the cellulose’s “specific surface area”, SSA) and to identify which substrate characteristic are key to enhancing accessibility during biomass pretreatments. As well as the source of the biomass (i.e. agricultural, softwood, hardwood) and how it has been collected, initially transported and stored (i.e. chips/straw/pellets, moisture content, particle size, etc.) it is likely that substrate characteristics at each of the fiber, fibril and microfibril levels will all influence the SSA. The pulp and paper sector has traditionally used various techniques such as determining the water retention value to give a general indication of biomass “swelling”, to more quantitative methods such as solute exclusion and Simons staining to assess the porosity or cellulose accessibility of a pretreated substrate. The Simons stain technique in particular has proven to be invaluable as it provides a good assessment of the SSA of a range of lignocellulosic substrates regardless of factors such as the pretreatment, pulping, swelling, decrease particle size, etc., methods used to increase cellulose accessibility.  Due to the enriched, direct orange (DO) dye’s approximate similarity in size to cellulases and its high affinity for cellulose, it provided a good indication of the accessibility/SSA of the cellulose present in various pretreated substrates, resulting in an R² value of 0.87 when plotted against enzymatic hydrolysis yields.