Gluconic acid pretreatment of tobacco stems for hydrolysate production and fermentation

Tobacco stems are lignocellulosic residues generated during tobacco processing, but their conversion into fermentable sugars is limited by the recalcitrant cell-wall structure. Although gluconic acid pretreatment has been applied to several lignocellulosic feedstocks as a bio-based organic acid strategy, its effects on tobacco stems remain unclear. This study investigated gluconic acid pretreatment as a route to improve cellulose accessibility and sugar recovery from tobacco stems. The optimal GA pretreatment performance was obtained with 10.00% gluconic acid at 170 °C, which removed 70.9% of hemicellulose, increased the cellulose content to 61.3%, and gave the highest enzymatic hydrolysis efficiency of 35.5%. Pretreatment also altered crystallinity and surface area, contributing to improved cellulase accessibility. During enzymatic hydrolysis at an elevated solids loading, glucose concentration reached 74.8 g/L at 15% solids loading after 96 h. Based on mass balance analysis, 1000 g of dry tobacco stems produced 344 g glucose and 31 g xylose, corresponding to an overall cellulose-to-glucose conversion rate of 71.3%. The resulting hydrolysate supported butyric acid and bacterial cellulose fermentation, suggesting that it could replace glucose in fermentation media. This study demonstrates that gluconic acid pretreatment is a promising strategy for tobacco stem valorization, providing insights into the further application of gluconic acid pretreatment and the utilization of agricultural residues.