Enhanced High-Solids Fed-Batch Enzymatic Hydrolysis of Sugar Cane Bagasse with Accessory Enzymes and Additives at Low Cellulase Loading

High cellulase loading is still a major impediment in the production of fermentative sugars from high-solids enzymatic hydrolysis of lignocellulosic substrates in the enzyme-based "biorefinery" industry. This study attempted a high-solids (20%) enzymatic hydrolysis of lignocellulosic substrate at a very low cellulase loading with mixed use of additives and accessory enzymes by fed-batch mode. To avoid the high initial biomass viscosity, the high-solids enzymatic hydrolysis of lignocellulosic substrates was initiated with a solids content of 8%. Thereafter, 4% of the additional substrates were consecutively fed into the hydrolysis system after 6, 12, and 18 h to reach a final solids content of 20%. Some additive mixtures (40 mg/g substrateTween 80 + 10 mg/g substrate tea saponin +20 mg/g substrate BSA) were observed to enable this fed-batch hydrolysis to increase 30% of the glucose yield after the 48 h. The combination of these additives and accessory enzymes (2.4 mg/g substrate xylanase and g substrate AA9) in the high-solids hydrolysis system further boosted the sugar release. This allowed us to achieve an industrially relevant sugar yield (83% cellulose and 90% xylan hydrolysis) and fermentable sugar titer (similar to 160 g/L) after 72 h, with a low cellulase enzyme loading (3 FPU/g substrate). Our results indicate that the fed-batch substrate addition process is a favorable model for high-solids enzymatic hydrolysis of lignocellulosic substrates. Moreover, the synergism between the additives and accessory enzymes can greatly boost the high-solids enzymatic hydrolysis of lignocellulosic substrates.