Elevated enzymatic hydrolysis by optimization of ultrasonication pretreatment of oil palm empty fruit bunch for glucose production

This study aims to obtain the optimum conditions of ultrasonication pretreatment using response surface methodology (RSM) with Box Behnken Design (BBD) as a first step before going to glucose production by enzymatic hydrolysis. The variables used in the ultrasonication optimization process include temperature (35–55 °C), time (25–65 min), and sulfuric acid concentration (0–1% v/v), with percent cellulose obtained as the response parameter. The optimum conditions for ultrasonication were at temperature of 45,3 °C, a time of 52 min, and an acid concentration of 1%. As a result, the relative cellulose content of oil palm empty fruit bunch (OPEFB) increased from 32.36 to 44.35%. It was found that ultrasound pretreatment can significantly reduce the extractive content of OPEFB. The use of diluted acid also reduces hemicellulose and loosens the bonds between lignin, which leads to an increase of glucose during the enzymatic hydrolysis process. Enzymatic hydrolysis using cellulase from Trichoderma reseii was then carried out, producing 26.5% of glucose yield which is 3 times higher compared to unpretreated (6.6% glucose yield) after 36 h. Examination by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Scanning Electron Microscope (SEM) was able to reveal how the ultrasonic pretreatment affects the microscopic structure, chemical, and physical properties of the OPEFB leading to improvement of the enzymatic conversion to glucose.