Abstract
Huge quantities of oil palm (Elaeis guineensis Jacq.) leaves (OPL) are generated as agricultural biomass from oil palm plantations. OPL are known to contain significant amounts of flavonoids. For maximal exploitation of these valuable antioxidant compounds, an innovative and sustainable extraction method employing natural deep eutectic solvents (NaDES) combined with ultrasonic assisted extraction was developed. Various NaDES composed of choline chloride as the hydrogen bond donor (HBD) and 1,2 propanediol (PD), 1,4 butanediol (BD), glycerol (GLY), glucose (GLU), maltose (MAL), and lactic acid (LA) as the hydrogen bond acceptor (HBA) were synthesized. The influence of these compositions, the methods of their synthesis, molar ratios, and water contents on their capacity to extract flavonoids from OPL was evaluated. Based on the results, it was found that methods which incorporate a heating step produced NaDES with the best capacity to extract OPL flavonoids. These thermal methods combined with molar ratios of 1:3 or 1:4 and water contents of 17 to 50% were found to be the optimal conditions for preparing NaDES, specifically when applied to the PD, BD, and GLY NaDES. Subsequently, UHPLC-UV/PDA-MS/MS analysis revealed NaDES extracts recovered by macroporous adsorption resin XAD7HP were able to optimally extract at least twelve luteolin and apigenin derivatives in OPL NaDES extracts prepared from glycerol and 1,4-butanediol demonstrated better and comparable efficiency as aqueous methanol in extracting flavonoids from OPL. The in vitro studies of antioxidant and wound healing properties supported these findings by exhibiting good free radical scavenging, cell proliferation, and migration activities. Additionally, the NaDES extracts also showed non-cytotoxicity effects at 1000 µg/mL and below on 3T3 fibroblast cells. Results of the study showed that NaDES could be a promising eco-friendly green solvent to extract bioactive OPL flavonoids that have great potential for applications as wound healing agents.
Highlights
Natural deep eutectic solvent (NaDES) is a generation of a new and revolutionary green solvent developed from the principle of ionic liquids (ILs) and deep eutectic solvents (DES) [1]
The combined supernatant was vacuum evaporated followed by solid-phase extraction (SPE) to remove residual NaDES which, due to its non-volatility, trace amounts of it were still present after vacuum evaporation
The low total flavonoid content (TFC) value of all the NaDES prepared at 1:5 molar ratio indicated the disproportionate amount of hydrogen bond donor (HBD) components (1,2 propanediol, 1,4 butanediol, glycerol, glucose, maltose, and lactic acid) with hydrogen bond acceptor (HBA), which resulted in an inefficient NaDES for flavonoid extraction
Summary
Natural deep eutectic solvent (NaDES) is a generation of a new and revolutionary green solvent developed from the principle of ionic liquids (ILs) and deep eutectic solvents (DES) [1]. Previous studies have reported that NaDES could extract flavonoids from different plant materials as efficiently as COS [4,24,25]. We prepared and optimized various compositions of NaDES for the extraction of flavonoids from OPL, and evaluated the feasibility of incorporating it in the aforementioned integrated process as an alternative green solvent in place of COS. Extracts obtained using the optimal choline chloride-based NaDES formulation were recovered using macroporous resin XAD7HP and further chemically profiled using ultra-high-performance liquid chromatography ultraviolet visible/photodiode array tandem mass spectrometry (UHPLC-UV/PDA-MS/MS). To ascertain the quality and potential biological applications of the end product obtained through the integrated process, the antioxidant and wound healing activities of the NaDES extracts were evaluated. Asa agreen greenstrategy strategyfor forflavonoid flavonoid extraction from oil palm leaves extraction from oil palm leaves (OPL)
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