Oxidative enzymes affect industrial strategy for lignocellulosic bioethanol at high dry matter content

Cost and performance of cellulolytic enzyme preparations are crucial for commercialization of second generation bioethanol technologies. Techno-economic assessments of bioprocesses imply very high dry matter content for economic efficiency. New advanced cellulolytic preparations has been found to alter the common perception regarding production strategies at industrial conditions. At 30% dry matter, separate hydrolysis and fermentation (SHF) performed significantly better (90% cellulose to ethanol conversion) than simultaneous saccharification and fermentation (70% final yield), which is contrary to many previous studies conducted with ancestor enzymatic preparations or at low dry matter conditions which are far away from industrial common practice. This change in the historical paradigm is due to incorporation in newer cellulolytic mixture of highly active β-glucosidases and the new class of oxidative enzymes LPMO’s.
Using a new designed bioreactor capable of efficiently mixing the hydrolyzates at up to 40% dry matter it was possible to study the kinetics of LPMOs enzymes while acting on lignocellulose in both strategies (SHF and SSF) at industrial relevant conditions. The results revealed that it was possible to correlate the higher ethanol amount produced during aerobic SHF with a correspondent higher activity of LPMO. The activity of this oxidizing enzyme requires, among others factors, the presence of oxygen. Thus during anaerobic SSF conditions it was possible to observe that the depletion of oxygen reduced the LPMO activity and resulted in lower final ethanol yield. This finding add an important piece to the puzzle regarding function of these new enzymes for a better exploitation in biorefineries.