New Approaches for the Extraction of Anthocyanins from Grape Skins Using Deep Eutectic Solvents

The effects of a hydrogen bond acceptor and hydrogen bond donor on carbon dioxide absorption via natural deep eutectic solvents were studied in this work. Naturally occurring non-toxic deep eutectic solvent constituents were considered; choline chloride, b-alanine, and betaine were selected as hydrogen bond acceptors; lactic acid, malic acid, and fructose were selected as hydrogen bond donors. Experimental gas absorption data were collected via experimental methods that uses gravimetric principles. Carbon dioxide capture data for an isolated hydrogen bond donor and hydrogen bond acceptor, as well as natural deep eutectic solvents, were collected. In addition to experimental data, a theoretical study using Density Functional Theory was carried out to analyze the properties of these fluids from the nanoscopic viewpoint and their relationship with the macroscopic behavior of the system, and its ability for carbon dioxide absorption. The combined experimental and theoretical reported approach work leads to valuable discussions on what is the effect of each hydrogen bond donor or acceptor, as well as how they influence the strength and stability of the carbon dioxide absorption in deep eutectic solvents. Theoretical calculations explained the experimental findings, and combined results showed the superiority of the hydrogen bond acceptor role in the gas absorption process, with deep eutectic solvents. Specifically, the cases in which choline chloride was used as hydrogen bond acceptor showed the highest absorption performance. Furthermore, it was observed that when malic acid was used as a hydrogen bond donor, it led to low carbon dioxide solubility performance in comparison to other studied deep eutectic solvents. The cases in which lactic acid was used as a hydrogen bond donor showed great absorption performance. In light of this work, more targeted, specific, deep eutectic solvents can be designed for effective and alternative carbon dioxide capture and management.

Recovery of rare earth elements from coal flyash using deep eutectic solvents as leachants and precipitating as oxalate or fluoride

Soursop (Annona muricata L.) leaves are rich in bioactive compounds with promising pharmacological and food applications. Deep eutectic solvents (DESs), a class of green and tunable solvents, offer an efficient and sustainable alternative to their extraction. This study investigates the use of various DES formulations for extracting bioactive compounds from soursop leaves under optimized conditions, considering the temperature, solvent-to-biomass ratio, and extraction time in a solid-liquid system. Conventional techniques, such as magnetic stirring and ultrasonic bath extraction, were also evaluated for comparison. DESs were prepared using choline chloride and menthol as hydrogen bond acceptors (HBAs) combined with lactic acid, oxalic acid, and 1,2-propanediol as hydrogen bond donors (HBDs). The optimal extraction conditions were determined at 50 °C with a biomass-to-solvent ratio of 1:10 (m/v). Solvent performance and interactions with biomass were analyzed using NMR, FTIR, density, viscosity, pH, and total humidity assessments. Compared to water and ethanol, DESs exhibited superior efficiency and stability, enhancing cell wall disruption and improving extraction yields. Among the tested solvents, acidic DES (CCAO) demonstrated the highest extraction efficiency despite its high viscosity and density. These findings pave the way for future applications in the pharmaceutical and food industries, reinforcing DESs as a promising environmentally friendly alternative for the extraction of high-value bioactive compounds from plant biomass.

This study investigated the influence of deep eutectic solvent (DES) acidity/alkalinity on the extraction profiles of phenolics and other biomolecules (phytic acid, reducing sugar, and protein) in defatted rice bran (DFRB). The DES with varying pH levels were prepared using different hydrogen bond acceptors (choline chloride (ChCl) and potassium carbonate (K2CO3)) and hydrogen bond donors (lactic acid, urea, and glycerol). The results reveal that the acidic DES (ChCl-lactic acid; pH 0.42) demonstrated superior extraction efficiency for total phenolic acids (4.33 mg/g), phytic acid (50.30 mg/g), and reducing sugar (57.05 mg/g) while having the lowest protein content (5.96 mg/g). The alkaline DES (K2CO3-glycerol; pH 11.21) showed the highest levels of total phenolic acid (5.49 mg/g) and protein content (12.81 mg/g), with lower quantities of phytic acid (1.04 mg/g) and reducing sugar (2.28 mg/g). The weakly acidic DES (ChCl-glycerol; pH 4.72) exhibited predominantly total phenolics (3.46 mg/g) with lower content of protein (6.22 mg/g), reducing sugar (1.68 mg/g) and phytic acid (0.20 mg/g). The weakly alkaline DES (ChCl-urea; pH 8.41) resulted in lower extraction yields for total phenolics (2.81 mg/g), protein (7.45 mg/g), phytic acid (0.10 mg/g), and reducing sugar (7.36 mg/g). The study also explored the distribution of phenolics among various DESs, with the alkaline DES (K2CO3-glycerol) containing the highest concentration of free phenolics. Notably, ChCl-based DESs predominantly contained soluble esterified bound phenolics and soluble glycosylated bound phenolics. Furthermore, a significant correlation between antioxidant activities and phenolic contents was observed. In conclusion, this study has revealed that the acidity and alkalinity of a DES significantly impact the extraction of phenolics and other value-added biomolecules in DFRB. These findings highlight the potential for manipulating the properties of DESs through pH variation, making them versatile solvents for extracting and isolating valuable compounds from agricultural by-products like DFRB and offering opportunities for sustainable utilization and value addition in various industries.

Green and enhanced extraction of bioactive ingredients from medicinal plants has become a hot research field, and deep eutectic solvents have been considered as a novel kind of sustainable solvents in the extraction process. In this study, hydrogen bond acceptor (choline chloride, etc.) and hydrogen bond donor (l-malic acid, etc.) were used to prepare different kinds of deep eutectic solvents to extract coumarins from Cortex Fraxini. The extraction conditions, including the composition and moisture content of deep eutectic solvents, extraction time, and liquid-solid ratio, were systematically optimized basing on the extraction yield of coumarins. To further investigate the extraction mechanism, Fourier transform infrared spectroscopy was performed, and the microstructures of Cortex Fraxini powders were observed before and after extraction using scanning electron microscope. Results showed that the novel ultrasound-assisted extraction with conditions of deep eutectic solvent containing betaine/glycerin (1:3), aqueous solution (20%), solid-liquid ratio (15mg/mL), and extraction time (30min) exhibited the best extraction yields for the four target coumarins and much better extraction efficiency than with conventional solvent extractions. This suggests that the new ultrasound-assisted deep eutectic solvent extraction could be used as a green and high-efficient approach for extraction of the main coumarins from Cortex Fraxini.

Deep eutectic solvents (DESs) were investigated as tunable, environmentally benign, yet superior extraction media to enhance the extraction of anthocyanins from grape skin, which is usually discarded as waste. Ten DESs containing choline chloride as hydrogen bond acceptor combined with different hydrogen bond donors were screened for high extraction efficiencies based on the anthocyanin extraction yields. As a result, citric acid, D-(+)-maltose, and fructose were selected as the effective DES components, and the newly designed DES, CM-6 that is composed of citric acid and D-(+)-maltose at 4:1 molar ratio, exhibited significantly higher levels of anthocyanin extraction yields than conventional extraction solvents such as 80% aqueous methanol. The final extraction method was established based on the ultrasound-assisted extraction under conditions optimized using response surface methodology. Its extraction yields were double or even higher than those of conventional methods that are time-consuming and use volatile organic solvents. Our method is truly a green method for anthocyanin extraction with great extraction efficiency using a minimal amount of time and solvent. Moreover, this study suggested that grape skin, the by-products of grape juice processing, could serve as a valuable source for safe, natural colorants or antioxidants by use of the eco-friendly extraction solvent, CM-6.

Structural studies of Myceliophthora Thermophila Laccase in the presence of deep eutectic solvents

Using the basic principle of construction between a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD), four bio-based deep eutectic solvents (DESs) were prepared in a 1:2 molar ratio of HBA:HBD. 2,3-Dihydroxypropyl-1-triethylammonium chloride ([C9H22N+O2]Cl−) was synthesized from raw glycerol and used as an HBA. Lactic acid, urea, pure glycerol, and ethylene glycol were selected as HBD. Attempts to prepare DESs, using citric acid and benzoic acid as HBDs, were unsuccessful. All these DESs were characterized using FTIR and NMR techniques. Besides, physicochemical parameters such as pH, viscosity, density, and melting point were determined. The behavior of these DES to fractionate olive pomace was studied. Lignin recovery yields spanned between 27% and 39% (w/w) of the available lignin in olive pomace. The best DES, in terms of lignin yield ([C9H22N+O2]Cl− -lactic acid), was selected to perform a scale-up lignin extraction using 40 g of olive pomace. Lignin recovery on the multigram scale was similar to the mg scale (38% w/w). Similarly, for the holocellulose-rich fractions, recovery yields were 34% and 45% for mg and multi-gram scale, respectively. Finally, this DES was used to fractionate four fruit pruning samples. These results show that our novel DESs are alternative approaches to the ionic liquid:triethylammonium hydrogen sulfate and the widely used DES: choline chloride:lactic acid (1:10 molar ratio) for biomass processing.

Deep eutectic solvents (DESs) are evolving as green extraction media in the search for efficient extraction of bioactive compounds. In the current study, four different choline chloride based DESs (eutectics of Choline chloride with ethylene glycol, malic acid, oxalic acid, and tartaric acid) were prepared with their physico-chemical properties and cytotoxicity evaluation. The FT-IR spectra of all solvents showed a very strong and broad band at 3350–3450 cm−1 due to intermolecular hydrogen bonding between choline chloride and hydrogen bond donors. The DESs were employed for the ultrasound-assisted extraction (UAE) of bioactive compounds from Cymbopogon citratus (lemongrass) to signify the extraction efficiency of DESs over aqueous methanol. The optimization of extraction parameters (time, temperature and biomass to solvent ratio) was done using Box–Behnken design (BBD). These solvents have negligible values of cytotoxicity in the range of 3.67 to 10.20%. The extraction yields obtained with DESs were significantly higher than aqueous methanol. The highest quantities of total phenolic contents (TPC) 116 mg GAE/g dry matter, total flavonoids contents (TFC) 98 mg QE/g dry matter and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition 95% were assessed with choline chloride/ethylene glycol solvent due to reduced viscosity. The maximum inhibition zones 45 ± 1.2 mm and 40 ± 1.3 mm against bacterial strains S. aureus and E. coli, respectively and 38 ± 1.2 mm and 29 ± 0.5 mm against fungal strains F. solani and A. niger, respectively were observed by choline chloride/ethylene glycol solvent. The DESs have revealed considerable high extraction yield due to extensive hydrogen bonding, which ultimately relates to the higher antioxidant and antimicrobial activities. The developed DESs would be the best alternative for the green and efficient extraction of phenolic compounds from natural sources.

Quantum chemical investigation of choline chloride-based deep eutectic solvents

A novel process based on low-energy mechanical pulp and deep eutectic solvents (DESs) was evaluated with the goal of producing fibers suitable for papermaking. Ideally, these fibers could be produced at much lower costs, especially when applied to an existing paper mill equipped with a thermomechanical pulp (TMP) production line that was threatened with shutdown due to the decreasing demand for wood-containing paper grades. The efficiency of DES delignification in Teflon-coated autoclaves and in a specially designed non-standard flow extractor was evaluated. All tested DESs had choline chloride ([Ch]Cl) as the hydrogen bond acceptor. Lactic acid, oxalic acid, malic acid, or urea acted as hydrogen bond donors. The temperatures and times of the delignification tests were varied. Chemical analysis of the pulp samples revealed that DESs containing lactic acid, oxalic acid, or urea decreased the lignin content by approximately 50%. The DES delignification based on [Ch]Cl and urea exhibited good hemicellulose retention while DES systems based on organic acids resulted in varying hemicellulose losses. The [Ch]Cl / urea mixture did not appear to be corrosive to stainless steel, which was another advantage of this DES system.

Response surface optimization for deep eutectic solvents extraction of bamboo shoots proteins

In this work, we investigated the effects of a single covalent link between hydrogen bond donor species on the behavior of deep eutectic solvents (DESs) and shed light on the resulting interactions at molecular scale that influence the overall physical nature of the DES system. We have compared sugar-based DES mixtures, 1:2 choline chloride/glucose [DES(g)] and 1:1 choline chloride/trehalose [DES(t)]. Trehalose is a disaccharide composed of two glucose units that are connected by an α-1,4-glycosidic bond, thus making it an ideal candidate for comparison with glucose containing DES(g). The differential scanning calorimetric analysis of these chemically close DES systems revealed significant difference in their phase transition behavior. The DES(g) exhibited a glass transition temperature of -58°C and behaved like a fluid at higher temperatures, whereas DES(t) exhibited marginal phase change behavior at -11°C and no change in the phase behavior at higher temperatures. The simulations revealed that the presence of the glycosidic bond between sugar units in DES(t) hindered free movement of sugar units in trehalose, thus reducing the number of interactions with choline chloride compared to free glucose molecules in DES(g). This was further confirmed using quantum theory of atoms in molecule analysis that involved determination of bond critical points (BCPs) using Laplacian of electron density. The analysis revealed a significantly higher number of BCPs between choline chloride and sugar in DES(g) compared to DES(t). The DES(g) exhibited a higher amount of charge transfer between the choline cation and sugar, and better interaction energy and enthalpy of formation compared to DES(t). This is a result of the ability of free glucose molecules to completely surround choline chloride in DES(g) and form a higher number of interactions. The entropy of formation for DES(t) was slightly higher than that for DES(g), which is a result of fewer interactions between trehalose and choline chloride. In summary, the presence of the glycosidic bond between the sugar units in trehalose limited their movement, thus resulting in fewer interactions with choline chloride. This limited movement in turn diminishes the ability of the hydrogen bond donor to disrupt the molecular packing within the lattice structure of the hydrogen bond acceptor (and vice versa), a crucial factor that lowers the melting point of DES mixtures. This inability to move due to the presence of the glycosidic bond in trehalose significantly influences the physical state of the DES(t) system, making it behave like a semi-solid material, whereas DES(g) behaves like a liquid material at room temperature.

Pretreatment is still the most expensive step in lignocellulosic biorefinery processes. It must be made cost-effective by minimizing chemical requirements as well as power and heat consumption and by using environment-friendly solvents. Deep eutectic solvents (DESs) are key, green, and low-cost solvents in sustainable biorefineries. They are transparent mixtures characterized by low freezing points resulting from at least one hydrogen bond donor and one hydrogen bond acceptor. Although DESs are promising solvents, it is necessary to combine them with an economic heating technology, such as microwave irradiation, for competitive profitability. Microwave irradiation is a promising strategy to shorten the heating time and boost fractionation because it can rapidly attain the appropriate temperature. The aim of this study was to develop a one-step, rapid method for biomass fractionation and lignin extraction using a low-cost and biodegradable solvent. In this study, a microwave-assisted DES pretreatment was conducted for 60 s at 800 W, using three kinds of DESs. The DES mixtures were facilely prepared from choline chloride (ChCl) and three hydrogen-bond donors (HBDs): a monocarboxylic acid (lactic acid), a dicarboxylic acid (oxalic acid), and urea. This pretreatment was used for biomass fractionation and lignin recovery from marine residues (Posidonia leaves and aegagropile), agri-food byproducts (almond shells and olive pomace), forest residues (pinecones), and perennial lignocellulosic grasses (Stipa tenacissima). Further analyses were conducted to determine the yield, purity, and molecular weight distribution of the recovered lignin. In addition, the effect of DESs on the chemical functional groups in the extracted lignin was determined by Fourier-transform infrared (FTIR) spectroscopy. The results indicate that the ChCl-oxalic acid mixture affords the highest lignin purity and the lowest yield. The present study demonstrates that the DES-microwave process is an ultrafast, efficient, and cost-competitive technology for lignocellulosic biomass fractionation.

Conversion of sunflower stalk based cellulose to the valuable products using choline chloride based deep eutectic solvents