Hydrothermal alkaline sulfite pretreatment in the delivery of fermentable sugars from sugarcane bagasse

Abstract

This work aims to demonstrate the importance of hydrothermal alkaline sulfite pretreatment of sugarcane bagasse in the delivery of fermentable sugars. The pretreatment conditions, namely sodium sulfite loads (5.0–10.0 wt%), temperatures (140–160 °C) and reaction times (30–60 min), were tested according to the full factorial design of experiments. The employed pretreatment was characterized by high lignin removal (43–77 wt%) and partial extraction of xylans (up to 25.0 wt%), mainly by cleavage of acetyl and arabinosyl groups. After 72 h of enzymatic hydrolysis with 10 FPU (filter paper unit) cellulase and 10 CBU (cellobiose unit) β-glucosidase per g of pretreated bagasse, the conversion of the carbohydrate-enriched substrates was in the range of 51 to 80 mol% for cellulose and 45 to 71 mol% for xylans. The best hydrothermal alkaline sulfite pretreatment conditions (10.0 wt% sulfite load, 150 °C and 45 min) were found to be highly efficient for the delivery of fermentable sugars with a yield as high as 40.4 ± 1.9 g for 100 g native bagasse.