17-10: Comparing SHF and SSF processing of wheat straw, at high dry matter conditions (30% DM), upon enzymatic oxidation and hydrolysis of cellulose

Higher yields in enzymatic saccharification of lignocellulosic biomass has for long been needed. The major aspects pursuing this goal are: enzymes performance and process optimization. Enzyme producers have improved the efficiency of their later generation enzyme mixtures by e.g. adding lytic polysaccharide monooxygenases (LPMOs, previously known as GH61s).To improve the cost competiveness of the process a key factor is to increase the dry matter (DM) content during all steps: from pre-treatment to hydrolysis and fermentation.

We have studied how the new generation of cellulolytic enzymes affects the strategies for lignocellulosic ethanol fermentation at industrial relevant conditions (30% DM). An SHF strategy leads to 30% higher conversion of cellulose to ethanol than SSF when applying more recent generation products (CellicCTec2), and generally higher yields when compared with earlier editions of enzyme cocktails (Celluclast and Novozyme188). Since LPMO activity is a major part of CTec2, oxidized products were measured as a diagnostic element of LPMOs activity: a higher amount of gluconic acid was found in SHF than in SSF. Thus, the effects of process design as well as the biomass recalcitrance were studied in relation to the LPMOs activity. Furthermore lignin was investigated as a natural molecular booster of GH61 in substitution of the well-known artificial ascorbic acid: a similar extent of boosting capacity from plant-derived molecules was observed [1]. Results suggest also that high dry matter (or low water activity) conditions are directly correlated to higher oxidative activity of LPMOs.

[1]  Cannella et al, Biotechnol Biofuels 5-26 (2012).