Application of Choline Chloride Based Deep Eutectic Solvent for the Extraction of Ferulic Acid from Oil Palm Pressed Fibre

"Extraction of ferulic acid from oil palm have been carried out in the past with alkaline hydrolysis and alcoholysis. However, the yields were low and the harsh extraction conditions were not favoured. Deep eutectic solvent (DES) serves as a new medium for efficient extraction of ferulic acid. Choline chloride based DESs were investigated for their application in the extraction of ferulic acid from palm pressed fibre. Two types of choline chloride based DESs were investigated, choline chloride-acetic acid (ChCl-AA) and choline chloride-citric acid (ChCl-CA) whereby acetic acid was found to be a better hydrogen bond donor to choline chloride than citric acid resulted in higher amount of ferulic acid extracted. Influence of water in DES was investigated whereby viscosity of ChCl-AA and ChCl-CA dropped from 9.678 ± 0.46 to 5.736 ± 0.38 mm2/s and 22.658 ± 0.65 to 10.22 ± 0.34 mm2/s, respectively as the water content in the DES increased from 0 to 50 wt%. The drop in viscosity contributed to higher extraction efficiency in which 41,155 ± 940 mg/kg ferulic acid was obtained from palm pressed fibre after 6 h reflux when ChCl-AA with 30 wt% water was used for the extraction compared to 30,940 ± 621 mg/kg when neat ChCl-AA was used. Although viscosity of the DES could be improved with addition of water, there is a threshold where the DES could tolerate the presence of water without changing its solvent behavior. The optimum condition for extraction of ferulic acid from palm pressed fiber was 6 h heating with DES containing 30 wt% water. Surface response model revealed that interaction between heating duration and water content in DES, as well as second order effect of both heating duration and water content in DES played important roles in the extraction of ferulic acid from oil palm pressed fiber.