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

Abstract

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 1 mg/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 (∼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.

Performance targets defined by retro-techno-economic analysis for the use of soybean protein as saccharification additive in an integrated biorefinery

“…However, increase of the solids loading led to decreases of cellulose conversion and process gain. These results were consistent with previous findings that increase of the solids loading enhanced glucose release, while it negatively affected cellulose conversion 14,32,33 . This decrease in conversion could be attributed to problems in mixing and mass transfer, together with the inhibition of cellulases by the products formed during the hydrolysis, which affected saccharification performance when using high solids loadings 32,33 .…”

“…In order to minimize this negative effect of lignin, the use of additives to mitigate the nonproductive binding has been investigated[10][11][12][13] . Among the additives that can be used to reduce the nonproductive adsorption of enzymes are non-ionic surfactants (Tween)14,15 , polymers (PEG -polyethylene glycol)16,17 and noncatalytic proteins (BSA -bovine serum albumin)11,13,16 , that bind into lignin mostly through hydrophobic interaction18,19 . However, there is still a need to evaluate the techno-economic impacts of these additives in the context of biorefineries for the production of 2G ethanol in large-scale industrial processes.…”

Hydrolysis and fermentation steps of a pretreated sawmill mixed feedstock for bioethanol production in a wood biorefinery

“…Depending on the assays, pretreated sawdust mixture solids could be oven-dried (110°C for 24h) or not. Enzymatic hydrolysis of pretreated mixture was performed in 150 mL Erlenmeyer flasks under batch conditions at 50°C in a shaker water bath (Julabo SW22, France) with a mixing speed of 180 rpm according to Mukasekuru et al (2018). Hydrolysis was carried out in a 50 mM acetate buffer solution at pH 4.8 using the cocktail of enzyme mentioned above and streptomycin antibiotics were added to prevent contamination.…”

Alkaline post-incubation improves the saccharification of poplar after hydrogen peroxide–acetic acid pretreatment

“…Moreover, some reports obtained relatively low glucose yields (less than 65.0%) from pretreated poplar and the cellulase loading were higher than 15 FPU/g DM [ 40 – 42 ]. Furthermore, the enzymatic hydrolysis of HPAA-pretreated lignocelluloses needs extra cellulase or surfactant to improve hydrolysis yield [ 11 , 43 , 44 ]. Herein, more than 95.0% glucose yields were got from poplar and only 10 FPU CTec2 per g DM was used in the enzymatic hydrolysis without extra cellulase or surfactant.…”