Response Surface Optimization of Enzymatic Hydrolysis of Sugar Beet Leaves into Fermentable Sugars for Bioethanol Production

Abstract

Sugar beet leaves are the major crop waste from sugar beet production, while the unused leaves contain a high number of sugars and polysaccharides. The effects of different enzyme products (cellulase, Cellic CTec2; xylanase, Cellic HTec2; and pectinase, Pectinex Ultra SPL) were determined during high-solids enzymatic hydrolysis of sugar beet leaves at 10% total solids (TS) content. Response surface methodology was used to study the effects of enzyme loadings during the hydrolysis of sugar beet leaves for producing fermentable sugars. It was found that both cellulases and pectinases are important enzymes for the hydrolysis of sugar beet leaves. Enzyme loading and reaction time were important factors. Based on the amount of sugars released, a maximum sugar conversion of 82% was achieved after 72 h of hydrolysis using 30 filter paper unit (FPU) g -1 glucan for cellulase and 150 polygalacturonase unit (PGU) g -1 polygalacturonic acid for pectinase, or 37 FPU g -1 glucan for cellulase and 100 PGU g -1 polygalacturonic acid for pectinase. The corresponding sugar yield and sugar concentration were 0.35 g·g -1 TS, and 35 g·l -1 , respectively. Sugar conversion ranged from 59% - 70%, 68% - 80%, and 74% - 82% after 24 h, 48 h, and 72 h of hydrolysis depending on the design conditions.