17-20: Optimization of Enzymatic Hydrolysis of Sugar Beet Leaves for Ethanol Production and Protein Recovery

Optimization of biofuel production and high value by-product recovery are critical for cost- and energy-effective biorefinery operations. While sugarbeet roots have been used as one of the primary feedstock for bioethanol production in Europe, sugar beet leaves accounting for 30-50% of the whole sugarbeet crop weight remain unused. This study was carried out to develop an efficient enzymatic hydrolysis process to convert beet leaves as a substrate model for leafy biomass into fermentable sugars and to recover protein as a valuable by-product. Response surface methodology was used to optimize the enzymatic hydrolysis of beet leaves at 12% total solid content using a mix of cellulases, hemicellulases and pectinases. The effect of enzyme concentrations was studied using a five-level rotatable central composite design for maximum conversion of sugar beet leaves to fermentable sugars. The results showed that cellulases, pectinases, and quadratic terms of each enzyme had significant effect on the response. The optimum enzyme loadings for achieving the maximum reducing sugars yield after 24 h of hydrolysis were 24 FPU/g cellulose for cellulase, 1171 XU/g hemicellulose for hemicellulase, and 136 PGU/g pectin for pectinase. The predicted reducing sugar release after 24 h of hydrolysis at the optimal points is 0.29 g RSS/g total solids, accounting for the maximum conversion efficiency of 71%. The model adequacy was satisfactory with coefficient of determination of 0.855. Peptides and proteins were recovered from sugar beet leaf hydrolysate and determined for the potential of producing leaf protein concentrate.