Effects of dilute acid pretreatment on enzyme saccharification of wheat stubble

BACKGROUND: Prehydrolysis of wheat stubble using moderate temperatures and dilute acid strength is an effective means for solubilizing hemicellulose fractions and improving cellulose hydrolysis. Variation in prehydrolysis parameters (temperature, time, and acid strength) and enzymatic saccharification conditions were examined for conversion of wheat stubble into fermentable sugars. RESULTS: Elevating temperature and acid strength maximized sugar release in prehydrolysate liquors. The optimal conditions of 2.0%H₂SO₄/60min/121°C, effectively solubilized 79% of the available hemicellulose. Production of inhibitory hydrolysis and degradation products such as acetic acid and levulinic acid, were detected at levels of 3.4gL⁻¹ and 0.64gL⁻¹, respectively. Sugar yields in prehydrolysate and saccharified liquors were found to increase with treatment severity. Temperature had the greatest impact on sugar release, followed by acid concentration and time. Optimizing prehydrolysis conditions at 1.0% H₂SO₄/90min/121°C, produced a 3.2-fold improvement in cellulose hydrolysis with recoveries approaching 82%. The addition of β-glucosidase and xylanase to the cellulase preparations assisted monomeric sugar release. CONCLUSION: Although treatment conditions for hemicellulose and cellulose hydrolysis differ, the study's findings suggest a good degree of overlap and process flexibility which should permit high recovery of pentose and hexose sugars.