Enhanced enzymatic hydrolysis of pretreated almond-tree prunings for sugar production

Almond-tree prunings (ATP), an agricultural residue largely available in Mediterranean countries, were pretreated with either hot water or dilute sulphuric acid at 180-230 degrees C. Solids derived from hot water pretreatments were further submitted to alkaline peroxide delignification. In addition, all solids obtained from the three mentioned processes were hydrolysed by cellulases and beta-glucosidases to investigate their enzymatic digestibilities. Hot water pretreatment led to high oligosaccharide yields (18.2 g/100 g ATP at 190 degrees C) while dilute acid pretreatment provided the highest monosaccharide yields (24.0 g/100 g ATP at 190 degrees C) along with low concentrations of fermentation inhibitors. Glucose yields from enzymatic hydrolysis were strongly affected by both pretreatment type and pretreatment temperature. The highest temperature assayed for both hydrothermal and dilute sulphuric acid pretreatment maximized the glucose recovery (49.2% and 72.8%, respectively) while solids derived from alkaline peroxide treatment achieved maximal glucose concentrations (41.9 g/L, 58.4% of potential yield). (C) 2013 Elsevier Ltd. All rights reserved.