3-34: The Development of More Representative Assays to Determine the Hydrolytic Performance of “Cellulase Mixtures” used to Obtain Effective Cellulose Hydrolysis of Pretreated Biomass

Various enzyme mediated, biomass-to-ethanol processes are currently being developed around the world. However the industry is still lacking a simple, accurate and reliable means of measuring and predicting the hydrolytic potential/performance of the cellulase mixtures that are used to hydrolyze the cellulose present in pretreated lignocellulosic substrates. Kinetic models generally provide a more detailed and phenomenological interpretation of hydrolysis mechanisms than they do in predicting the performance of an industrially relevant process such as enzymatic hydrolysis. However, it is anticipated that engineering practices for the design and scale-up of enzymatic hydrolysis processes will, at least initially, rely more on “semi-empirical” approaches. We have been looking at two ways of trying to assess the hydrolytic performance of a particular “cellulase mixture”. One is based on the linear relationship between hydrolysis yields and the logarithm of enzyme loading and the other on the nonlinear least-squares fitting of a semi-empirical model. In this way empirical predictive equations from which enzymatic hydrolysis indicators (e.g. specific enzyme performance indexes and biomass hydrolyzability) could be  determined and used to assess the degree of improvement of newly developed commercial cellulase mixtures on a range of industrially relevant biomass feedstocks pretreated by SO₂-catalyzed steam explosion. This approach was also used to assess the impact that industrially relevant process factors  such as, washing, unproductive binding, and the enzymatic hydrolysis mode used (whole slurry, separate hydrolysis, and hybrid hydrolysis and fermentation) might have on sugar yields obtained when high consistency (substrate concentration) hydrolysis was carried out at varying enzyme loadings.