Mild acid pretreatment and enzyme saccharification of Sorghum bicolor straw

Dilute sulphuric acid pretreatment followed by enzyme saccharification of Sorghum bicolor straw was undertaken to examine its potential as a feedstock in bioethanol production in Australia. Factorial design experiments evaluated the impact of pretreatment parameters on hemicellulose solubilisation and cellulose enzymatic hydrolysis. Sugar yields in prehydrolysate and saccharified liquors were found to increase with treatment severity; temperature was found to have the greatest impact. Degradation products were minimal; acetate and total phenolics peaked at 33 and 1.5 mg/g respectively. Conditions for maximum hemicellulose solubilisation (2% H2SO4 for 60 min at 121 °C) differed to those associated with maximum glucose release from solid residue saccharifications (1% H2SO4/90 min /121 °C). Water extractive sugars accounted for over 20% total sugars recovered. Addition of β-glucosidase and xylanase to enzyme saccharification enhanced reaction rates and final sugar yields three-fold, whilst reducing cellulase dosage. Considering its abundance, high sugar potential and apparent ease of conversion, sorghum straw is an appropriate feedstock for the production of second generation fuels.

► High xylose recovery and low acetate release in hydrolysate liquors.
► The solid fraction is acquiescent to enzyme digestion with high glucose release.
► High water extractive (sugar) content in sorghum straw.
► Dilute acid is effective in pretreating sorghum straw.