Combination of Lactic Acid-Based Deep Eutectic Solvents (DES) with β-Cyclodextrin: Performance Screening Using Ultrasound-Assisted Extraction of Polyphenols from Selected Native Greek Medicinal Plants

Chrysa Georgantzi, Antonia-Eleni Lioliou, Nikos Paterakis, Dimitris Makris
2017 Agronomy  
A series of novel L-lactic acid-based deep eutectic solvents (DES) were tested for polyphenol extraction performance, using organically grown, native Greek medicinal plants. The extractions were ultrasonically-assisted and the effect of the addition of β-cyclodextrin (β-CD) as extraction booster was also tested, at a concentration of 1.5% (w/v). The estimation of total polyphenol yield (Y TP ) suggested that DES composed of L-lactic acid and nicotinamide and L-lactic acid and L-alanine, both at
more » ... L-alanine, both at a molar ratio of 7:1, are promising solvents giving significantly higher yields compared with 60% (v/v) aqueous ethanol and water. However, when β-CD was combined with DES comprised of L-lactic acid and ammonium acetate (molar ratio 7:1), the extraction yields obtained in some instances were equal of even higher. The pattern was not consistent when the yield in total flavonoids (Y TFn ) was considered, indicating water, 60% (v/v) aqueous ethanol and L-lactic acid:sodium acetate (molar ratio 7:1) to be the most efficient solvents. In this case, the effect of β-CD was of rather lower magnitude. The examination of the antioxidant activity of the extracts generated showed that there is a close correlation mainly with their concentration in total polyphenols. Agronomy 2017, 7, 54 2 of 12 polyphenol-containing medicinal plants. The interest is on the development of highly performing and cost-effective downstream processes, which aim at producing commodities with crude or purified extracts. A critical parameter in such processes is the efficient retrieval of polyphenols, which is primarily carried out by solid-liquid extraction. The selection of an appropriate solvent is of paramount importance and profoundly defines yield and composition of the extracts produced. Most common solvents to date are of petrochemical origin [5] but they have several inherent disadvantages, being flammable and toxic, while their production is associated with fossil resources. A high number of examinations have been expended on the replacement of hazardous solvents with more eco-friendly alternatives, and in this regard biomass-derived materials offer unprecedented opportunities for green solvent production. Deep eutectic solvents (DES) are an innovative class of eco-friendly liquids comprised of bio-molecules, such as a polyol serving as the hydrogen bond donor (HBD), and an organic salt, which is the hydrogen bond acceptor (HBA) [6] . DES display attractive attributes, including negligible vapour pressure, tunability, lack of toxicity, low cost, etc. These features make DES ideal extraction solvents, possessing unique characteristics, whereas limitations associated with similar materials, such as conventional organic solvents and ionic liquids, may be overcome [7] . DES are usually less expensive, easy to produce (use of bulk commodity chemicals) and biodegradable and, depending on the composition, they may be compatible with foods, pharmaceuticals and cosmetics. Furthermore, tailoring their physicochemical properties could be crucial to manipulating their extraction potency, because several parameters (polarity, viscosity, hydrogen bonding) central to mass transport phenomena may be effectively regulated [8] . Cyclodextrins (CDs) are enzymicaly produced starch derivatives, and owed to the slightly hydrophobic inner surface of their ring-shaped molecules, they can form inclusion complexes with molecules of low hydrophilicity and suitable geometrical size. These cyclic oligosaccharides comprise of 6, 7 or 8 glucopyranose units (α-, βand γ-CDs, respectively) and they differ in size (0.5-0.9 nm in diameter) that determines the accommodation of the guest molecules into the cavity [9] . Recent examinations showed that combining 2-hydroxypropyl β-cyclodextrin with aqueous glycerol may result in increased yield of polyphenol extraction [10, 11] . Similar outcome was reported for water extraction of apple flavonols, using various cyclodextrins [12] . In this framework, this investigation was undertaken with the aim to screening the performance of polyphenol extraction from various organically grown native Greek medicinal plants, using a combination of β-CD with a series of L-lactic acid-based DES. Experimental Section Chemicals β-Cyclodextrin (98%) and ethanol (99.8%) were from Acros Organics (Geel, Belgium). Anhydrous sodium carbonate was from Carlo Erba Reactifs (Val de Reuil, France). Nicotinamide was from Fluorochem (Hadfield, UK). L-Alanine (99%) and choline chloride (99%) were from Alfa Aesar (Karlsruhe, Germany). Aluminium chloride hexahydrate, ammonium acetate, sodium acetate trihydrate, and L-lactic acid (80%) were from Penta (Prague, Czeck Republic). Glycine (99.5%) was from NeoLab Migge Laborbedarf-Vertiebs (Heildelberg, Germany). 2,4,6-Tripyridyl-s-triazine (TPTZ, 99%), Folin-Ciocalteu reagent and ferric chloride hexahydrate were from Fluka (Steinheim, Germany). 2,2-Diphenyl-1-picrylhydrazyl radical (DPPH), caffeic acid, ascorbic acid and rutin (quercetin 3-O-rutinoside) were from Aldrich (Steinheim, Germany). Preparation of DES Previously, reported methodologies were applied to synthesise all the DES tested [13] . Briefly, HBD (L-lactic acid) was mixed with each of the HBAs (Figure 1 ), in 100-mL glass vials, at HBD:HBA
doi:10.3390/agronomy7030054 fatcat:pxv4p7ugfvg2pkaxfpj6b5vry4