10-13: Substrate heterogeneity: What key biomass related factors influence the pretreatment and enzyme cocktail that should be used to achieve effective biomass conversion?

Nature has designed lignocellulosics as structural matrices resistant to breakdown by biological systems. Thus, a cheap and effective pretreatment to fractionate biomass into lignin, hemicellulose and a cellulose fraction easily hydrolyzed at low enzyme loadings is desired. However, biomass based industries such as pulp and paper have long recognized that variations in the feedstock biomass’s characteristics can have a profound influence on downstream processes. The biomass type (softwood, hardwood, agricultural) and its heterogeneity (i.e. the presence of  bark, leaves, particle size and moisture etc.) will influence the choice of pretreatment. We examined the ability of steam and organosolv pretreatments to generate substrates from various biomass samples that could be hydrolyzed with minimal enzyme loadings. Although not immediately obvious, many factors that influenced pretreatment effectiveness could be traced to substrate heterogeneity. For example, earlier work of the Consortia for Applied Fundamentals and Innovation(CAFI) indicated significant differences in pretreatment and enzymatic hydrolysis between two hybrid poplar samples. In this presentation, we tried to identify substrate characteristics that might influence the effectiveness of pretreatment.  For example, when comparing two pretreated corn stover samples, hydrolysis yields were 10-15% higher for the sample that retained more of the SO₂ catalyst. Furthermore, a linear trend was observed with the amount of xylan removed during pretreatment and improvements in hydrolysis yields of pretreated corn stover and poplar. However, similar trends were not observed for softwood. The need to select an “ideal” pretreatment/enzyme mixture for a particular biomass type which anticipates potential substrate heterogeneity will be discussed.