Pretreatment and enzymatic hydrolysis of sunflower hulls for fermentable sugar production

Abstract: Sunflower is a widely adapted crop and can be grown in every temperature region. In the U.S., two million acres were cultivated with sunflowers in 2009. During industrial processing, large quantities of hulls are obtained as a waste product from the dehulling process. This study focused on converting the sunflower hulls into fermentable sugars by dilute acid pretreatment and enzymatic hydrolysis. Raw sunflower hulls are composed of β-glucan (34%±1.1%), lignin (25%±0.95%), xylan and arabinan (27%±1.56%), extractives (13%±2.5%) and traces of ash. Sunflower hulls were first subjected to pretreatment by varying three independent factors: 1) acid concentration (0.5%-2%); 2) reaction temperatures (140-160℃); 3) reaction time (10-30 min). Slurry samples obtained after pretreatment were separated into liquid and solid fractions. Liquid fractions were analyzed for monomeric and oligomeric sugars and inhibitor products by High Pressure Liquid Chromatography (HPLC). Enzymatic saccharification was then performed on pretreated solid fractions to convert remaining cellulose (β- glucan) into fermentable sugars. The results showed an increase in acid concentration and reaction temperature gave high xylose yield in the liquid fraction. However, an increase in reaction time resulted in degradation of xylose into furfural. A quadratic model for xylose yield was formulated based on the experimental results. The maximum xylose yield predicted by the model was 62 % at 158 ℃ for 20 min at 1.75 % acid concentration. The maximum β-gluca