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

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.