Fermentable Sugar Production from the Peels of Two Durian (Durio zibethinus Murr.) Cultivars by Phosphoric Acid Pretreatment

Abstract

The potential of durian (Durio zibethinus Murr.) peel as feedstock for the production of fermentable sugars was evaluated. Durian peel biomass from two cultivars, monthong (Durio zibethinus Murr. cv. Monthong) and chanee (Durio zibethinus Murr. cv. Chanee), were pretreated with different concentrations (70%, 75%, 80%, and 85%) of phosphoric acid (H3PO4) at a moderate temperature of 60 °C for 60 min. The H3PO4-pretreated durian peel biomass was then subjected to enzymatic hydrolysis. Significantly higher glucan (44.74 ± 0.21%) content was observed in the monthong peel compared to the chanee peel (42.06 ± 0.28%). Phosphoric acid pretreatment caused the significant solubilization of the xylan and acid soluble lignin (ASL) contents. This enhanced the enzymatic hydrolysis process causing a significant increase in the hydrolysis efficiency and glucose concentration. The highest hydrolysis efficiency and glucose concentration were obtained after 72 h from the 75% H3PO4-pretreated peel biomass for both the monthong (90.33 ± 0.42% and 9.55 ± 0.11 g/L, respectively) and chanee (90.06 ± 0.40% and 8.56 ± 0.13 g/L, respectively) peels. Biomass to glucose recovery for monthong and chanee were improved by approximately 7- and 6-fold, respectively. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis showed destruction of the peel biomass structure and changes in the cellulose crystallinity index (CrIs).