Tailoring whole slurry bioprocessing for sugary stovers to augment sugar production by integrating soluble and insoluble carbohydrates

Abstract

Obtaining sufficient concentrations of fermentable sugars from the polysaccharides of lignocellulosic materials represents a long-term challenge in achieving sustainable biorefineries. This work aimed to enhance sugar titers by employing high sugar-containing stovers (HSS) and combining its intrinsic soluble sugars with the two insoluble carbohydrates, namely cellulose and hemicellulose. Whole-slurry hydrolysis (WSH) was performed under low-to-high solid conditions using non-detoxified pretreated slurry, which exhibited a decrease in cellulose hydrolysis efficiency (CHE) from 89.08% to 42.1% as the solid loadings increased from 7% to 20%. A further WSH with detoxified slurry showed a significant increase in CHE from 42.1% to 59.52% at 20% solid loading, indicating that inhibitors present in the pretreated slurry had negative effects on CHE. Lower CHE with non-detoxified slurry accompanied by higher losses of cellulase and β-glucosidase activities, particularly at higher solid loadings. Therefore, systematic modification of WSH was performed by incorporating 2% syringic acid during pretreatment and 0.4% polyethylene glycol during saccharification, reformulating enzyme cocktails, and implementing a fed-batch experiment. These modifications resulted in a notable improvement in sugar production under high-solid loading (20%) and non-detoxified conditions, reaching 142.87 g/L total sugars with a CHE of 90.7%. These findings have revealed the potential of integrating soluble sugars with holocellulose for obtaining high-titer fermentable sugars in lignocellulosic biorefineries.