Pretreatment of sugarcane leaves to enhance cellulase hydrolysis for ehanol fermentation by Saccharomyces cerevisiae

Abstract

Sugarcane leaves pretreated by dilute sulfuric acid was more susceptible to cellulase than those pretreated by lime. Optimal condition for the dilute sulfuric acid pretreatment was 6% (w/v) substrate (20-40 mesh particle size) loading, 1.5% (w/v) H2SO4 at 121oC, 15 lb/in2, 30 min. Hydrolysis of the dilute sulfuric acid pretreated sugarcane leaves slurry by cellulase (10 FPU/g, dry weigh basis (DS): β-glucosidase 3.55 salicin Unit/ml) for 6h yield 0.057 glucose g/g DS. Hydrolysis of the dilute sulfuric acid pretreated sugarcane leaves by AcellulaseTM1000 at 160 FPU/g (DS) (β-glucosidase 400 pNPGU/g) for 6 h resulted in glucose 9.8 g/l. The glucose was further fermented to ethanol by Saccharomyces cerevisiae TISTR 5596 for 24 h. Ethanol yield was 4.71 g/l (0.48 g/g glucose) or 0.20 g/g cellulose (0.08 g ethanol/g (DS) sugarcane leaves). Pretreatment of sugarcane leaves by dilute sulfuric acid released xylose 0.11 g/g (DS) which was the same as glucose released after cellulase hydrolysis (0.12 g/g (DS)). So, both of xylose and glucose were fermented to ethanol by Pichia stipitis and S.cerevisiae TISTR 5596, respectively. Flask scale fermentation gave ethanol from xylose (3.12 g/l or 0.35 g/g xylose) at 96h, and from glucose (2.9 g/l or 0.46 g/g glucose) at 12h. Total ethanol yield in flask scale was 6.02 g or 0.10 g ethanol/g (DS) sugarcane leaves. Three liters scale fermentation in 5L fermenter gave ethanol from xylose (4.08 g/l or 0.47 g/g xylose) at 96h, and from glucose (3.05 g/l or 0.49 g/g glucose) at 12h. Total ethanol yield in 3L fermenter scale was 7.13 g or 0.12 g ethanol/ g (DS) sugarcane leaves.