Fermentable sugar recovery from durian peel by using ultrasound-assisted chemical pretreatment

Durian peel, an abundant waste in Malaysia could be a potential substrate for fermentable sugar recovery for value-added biochemical production. Common pretreatment such as acid or alkaline pretreatment resulted in the need for extensive solid washing which generated wastewater. Herein, this study aims to introduce sonication on top of chemical pretreatment to destruct lignin and reduce the chemical usage during the durian peel pretreatment process. In this study, the morphology and the chemical composition of the pretreated durian peels were studied. The sugar yield produced from the chemical pretreatment and the combined ultrasound and chemical pretreatment were compared. The morphology and chemical structure of durian peels were investigated by Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR) analysis and X-ray diffraction (XRD). The SEM images showed that the structural change became more significant when sonication was introduced. Second, XRD profile indicated a relatively higher crystallinity index and FTIR spectra displayed a lower intensity of lignin and hemicellulose for ultrasound plus alkaline (UB) pretreatment as compared to acid, alkaline and ultrasound plus acid (UA) pretreatment. UB and UA pretreatment portrayed higher yield (376.60 ± 12.14 and 237.38 ± 3.96 mg reducing sugar/g dry biomass, respectively) than their controls without the application of ultrasound. Therefore, it could be concluded that ultrasound was able to intensify the fermentable sugar recovery from durian peel by inducing physical and chemical effect of cavitation to alter the morphology of durian peel. Fermentation of UB treated durian peel resulted in 2.68 mol hydrogen/mol consumed sugar and 131.56 mL/L_medium/h of hydrogen productivity. This study is important because it will shed light on a way to handle durian waste disposal problems and generate fermentable sugars for the production of high value-added products.