Formulation and characterization of natural deep eutectic solvents (NADES) for simultaneous phenolics and carotenes extraction from fresh oil palm leaf

In this study, natural deep eutectic solvents (NADES), comprising choline chloride (ChCl) as hydrogen bond acceptor (HBA) with hydrogen bond donor (HBD) including glucose (Glu), fructose (Fru), xylose (Xyl), xylitol (Xyli), and glycerol (Gly), were formulated and characterized for simultaneous extraction of phenolic compounds (polar) and carotenoids (non-polar) from fresh oil palm leaves (OPL). pH, density, polarity, Fourier Transform Infrared Spectroscopy (FT-IR) and rheological analyses were conducted, with relation to the extraction efficiency achieved via homogenizer-assisted heating and stirring extraction approach. Among the NADES formulations tested, ChCl:Xyl (1:1) displayed the highest total phenolic content (TPC) at 20.23825 mg/g OPL, due to its optimal polarity at 49.4654 kcal ${\mathrm{mol}}^{-1}$ and a viscosity of 23288 mPa.s. The highest total carotenoid content (TCC) was observed in ChCl:Xyli (1:1) at 325.94 µg/g OPL, with a lower polarity at 50.0280 kcal ${\mathrm{mol}}^{-1}$. Despite having similar viscosity and polarity, ChCl:Fru (1:2) with a pH of 5.82 outperformed ChCl:Glu (1:1) with a pH of 6.72 due to enhanced phenolic compound solubility and stability. This study shed light on the potential of NADES, particularly in overcoming the challenge of high moisture content in OPL and other fresh biomasses, which often acted as a barrier during phytonutrients extraction.