Review on Extraction of Phenolic Compounds from Natural Sources Using Green Deep Eutectic Solvents

Application of an alkali destruction technique and natural deep eutectic solvent for greener extraction from peanut shells: optimization and extraction kinetics study

Peanut shells are an agricultural by-product rich in flavonoids, but their utilization is not high at present. This research developed a method for the rational utilization of flavonoids in peanut shells, which could enhance the comprehensive utilization of peanut resources. A green and efficient natural extraction technique based on a natural deep eutectic solvent (NADES) and alkaline destruction was exploited for the extraction of the flavonoids from peanut shells. NADES synthesized with DL-menthol (Me) and DL-lactic acid (LA) was selected as the solvent. KOH was used as a destructive agent that could destroy the structure of Me/LA, which could aid not only recovering the flavonoids, but also aid Me recovery and recycling. The NADES with the molar ratio of Me to LA of 1 : 4 showed a higher extraction capacity for flavonoids and better maintenance of antioxidant activity than water and ethanol. The maximum extraction efficiency was 23.33 mg rutin equivalents per g. In addition, the mass-transfer kinetics model of flavonoids extraction was established using Fick's second law, which well fitted the experimental results and proved that the temperature had a significant effect on the extraction efficiency. These results offered some insights for the research and exploitation of an environmentally friendly method to extract bio-active flavonoids for future applications in actual industrial manufacturing.

Liquefying Flavonoids with Terpenoids through Deep Eutectic Solvent Formation

The formation of deep eutectic solvents (DES) is tied to negative deviations to ideality caused by the establishment of stronger interactions in the mixture than in the pure DES precursors. This work tested thymol and menthol as hydrogen bond donors when combined with different flavonoids. Negative deviations from ideality were observed upon mixing thymol with either flavone or flavanone, two parent flavonoids that only have hydrogen bond acceptor (HBA) groups, thus forming non-ionic DES (Type V). On the other hand, the menthol systems with the same compounds generally showed positive deviations from ideality. That was also the case with the mixtures containing the more complex hydroxylated flavonoid, hesperetin, which resulted in positive deviations when mixed with either thymol or menthol. COSMO-RS successfully predicted the behavior of the solid-liquid phase diagram of the studied systems, allowing for evaluation of the impact of the different contributions to the intermolecular interactions, and proving to be a good tool for the design of DES.

Deep Eutectic Solvent as Green Solvent in Extraction of Biological Macromolecules: A Review

Greater awareness of environmental sustainability has driven many industries to transition from using synthetic organic solvents to greener solvents in their manufacturing. Deep eutectic solvents (DESs) have emerged as a highly promising category of green solvents with well-demonstrated and wide-ranging applications, including their use as a solvent in extraction of small-molecule bioactive compounds for food and pharmaceutical applications. The use of DES as an extraction solvent of biological macromolecules, on the other hand, has not been as extensively studied. Thereby, the feasibility of employing DES for biomacromolecule extraction has not been well elucidated. To bridge this gap, this review provides an overview of DES with an emphasis on its unique physicochemical properties that make it an attractive green solvent (e.g., non-toxicity, biodegradability, ease of preparation, renewable, tailorable properties). Recent advances in DES extraction of three classes of biomacromolecules—i.e., proteins, carbohydrates, and lipids—were discussed and future research needs were identified. The importance of DES’s properties—particularly its viscosity, polarity, molar ratio of DES components, and water addition—on the DES extraction’s performance were discussed. Not unlike the findings from DES extraction of bioactive small molecules, DES extraction of biomacromolecules was concluded to be generally superior to extraction using synthetic organic solvents.

Temperature Optimization by Electrochemical Method for Improving Antioxidant Compound Extraction Efficiency from Origanum vulgare L. and Its Application in a Bread Production

This study aims to evaluate the effect of extraction temperature on the electrochemical activity of antioxidant compounds in oregano extract and its application in a bread production. Temperature optimisation was performed by determining the electrochemical index (EI), calculated on the parameters of individual peaks observed on the square wave voltammograms (SWV). The highest value of EI (2.5758 µA/V) was observed at 85 °C for the oregano extract. The composition of several types of bread with oregano extract or dried oregano leaves was then proposed. To specify bread samples, both newly prepared and during their storage, their antioxidant properties were determined using FRAP (Ferric Reducing Antioxidant Power) and CUPRAC (Cupric Reducing Antioxidant Capacity) methods. The study revealed that the addition of extract from oregano or oregano leaves increased the antioxidant compounds content in the bread from 30% to more than 138% compared to the control bread samples. The performed sensory evaluation of the bread samples revealed their high acceptability. It was found that the stored bread with oregano leaves changed sensory qualities to a lesser extent compared to the bread with oregano extract.

Structure, degree of polymerization, and starch hydrolase inhibition activities of bird cherry (Prunus padus) proanthocyanidins

The structure of proanthocyanidins extracted from bird cherry fruits was characterized by HPLC-ESI/MS² and MALDI-TOF/MS analyses, and their subunits and mean degree of polymerization (mDP) were investigated by thiolysis reaction, and the inhibition activity against starch hydrolases measured using the high-throughput turbidity assay. This is the first mass spectrometric analysis to thoroughly investigate the structure and mDP of proanthocyanidins in bird cherry fruits. Bird cherry proanthocyanidins were categorized as oligomeric proanthocyanidins (mDP = 5.6), which constituted of (epi)gallocatechins and (epi)catechins. The proanthocyanidins increased from a (epi)gallocatechin-[(epi)catechin]₃ tetramer to a (epi)gallocatechin-[(epi)catechin]₁₁ dodecamer through the addition of one (epi)catechin with both A-type and B-type linkages. The proanthocyanidins had potent α-amylase and α-glucosidase inhibition activities with IC₅₀ values of 0.19 ± 0.01 µg/mL and 0.18 ± 0.006 µg/mL, comparing favorably to commercial drug acarbose. Bird cherry oligomeric proanthocyanidins are a promising starch hydrolase inhibitor for the application of potential functional food components.

Optimization of Deep Eutectic Solvent Extraction of Phenolic Acids and Tannins from Alchemilla vulgaris L

Alchemilla vulgaris L. is a good source of antioxidant components with an emphasis on phenolic acids and tannins. In this study, gallic acid, ellagic acid, and hydrolyzable tannins (HT) were extracted from this plant with different deep eutectic solvents (DESs), varying the amount of added H₂O, temperature and extraction time. Seventeen DESs (n = 3) were used for the extraction, of which choline chloride:urea (1:2) proved to be the most suitable. The selection of the best solvent was followed by the examination of the influence of the extraction type and parameters using response surface methodology (RSM). Gallic acid content was in the range of 0.00-1.89 µg mg^-1, ellagic acid content was 0.00-12.76 µg mg^-1 and hydrolyzable tannin (HT) content was 3.06-181.26 µgTAE mg^-1, depending on the used technique and the extraction conditions. According to the results, extraction by stirring and heating was the most suitable since the highest amounts of gallic acid, ellagic acid, and HT were extracted, and the obtained optimal values using response surface methodology (RSM) are confirmed by experimentally obtained values.

Novel insights on extraction and encapsulation techniques of elderberry bioactive compounds

BACKGROUND

Elderberry (Sambucus nigra L.) has been used in traditional medicine and as a supplement in many beverages and meals. Elderberry is a good source of bioactive flavonoids like quercetin, kaempferol, and rutin, as well as other phenolic compounds. Extraction techniques significantly influence the efficiency of extraction of bioactive compounds. Green chemistry elements such as safety, environmental friendliness, run-down or at least minimal contaminants, efficiency, and economic criteria should all be addressed by an effective bioactive extraction process. Furthermore, micro/nanoencapsulation technologies are particularly effective for increasing bioavailability and bioactive component stability.

SCOPE AND APPROACH

This review article comprehensively describes new developments in elderberry extraction and encapsulation. Elderberry is largely employed in the food and pharmaceutical industries due to its health-promoting and sensory characteristics. Elderberry has traditionally been used as a diaphoretic, antipyretic, diuretic, antidepressant, and antitumor agent in folk medicine.

KEY FINDINGS AND CONCLUSIONS

Conventional extraction methods (e.g. maceration and Soxhelt extraction) as well as advanced green techniques (e.g. supercritical fluids, pulsed electric field, emulsion liquid extraction, microwave, and ultrasonic extraction) have been used to extract bioactives from elderberry. Over the other protective measures, encapsulation techniques are particularly recommended to protect the bioactive components found in elderberry. Microencapsulation (spray drying, freeze drying, extrusion, emulsion systems) and nanoencapsulation (nanoemulsions, solid lipid nanoparticles and nanodispersions, nanohydrogels, electrospinning, nano spray drying) approaches for elderberry bioactives have been examined in this regard.

Influence of the extraction method on the recovery of bioactive phenolic compounds from food industry by-products

Agro-foodindustries generate colossal amounts of non-edible waste and by-products, easily accessible as raw materials for up-cycling active phytochemicals. Phenolic compounds are particularly relevant in this field given their abundance in plant residues and the market interest of their functionalities (e.g. natural antioxidant activity) as part of nutraceutical, cosmetological and biomedical formulations. In "bench-to-bedside" achievements, sample extraction is essential because valorization benefits from matrix desorption and solubilization of targeted phytocompounds. Specifically, the composition and polarity of the extractant, the optimal sample particle size and sample:solvent ratio, as well as pH, pressure and temperature are strategic for the release and stability of mobilized species. On the other hand, current green chemistry environmental rules require extraction approaches that eliminate polluting consumables and reduce energy needs. Thus, the following pages provide an update on advanced technologies for the sustainable and efficient recovery of phenolics from plant matrices.

Stability of Chlorogenic Acid from Artemisiae Scopariae Herba Enhanced by Natural Deep Eutectic Solvents as Green and Biodegradable Extraction Media

A green and inexpensive natural deep eutectic solvent (NADES) was screened and integrated with an ultrasonic technique for extracting chlorogenic acid (CGA) from artemisiae scopariae herba. Response surface methodology was employed to investigate significant factors and optimize their influence. Proline-malic acid exhibited an excellent extraction capacity with a yield of 28.23 mg/g under the optimal conditions of water content of 15% (wt), solid-liquid ratio of 1.0/10 (g/mL), ultrasonic power of 300 W, and extraction time of 25 min. Simultaneously, the stability and antioxidant activity analysis exhibited a better performance of CGA in NADES than that in water and ethanol. The hydrogen-bonding interaction between CGA and natural deep eutectic molecules enhanced the stability and meanwhile protected the antioxidant activity of CGA.

Latest Insights on Novel Deep Eutectic Solvents (DES) for Sustainable Extraction of Phenolic Compounds from Natural Sources

Phenolic compounds have long been of great importance in the pharmaceutical, food, and cosmetic industries. Unfortunately, conventional extraction procedures have a high cost and are time consuming, and the solvents used can represent a safety risk for operators, consumers, and the environment. Deep eutectic solvents (DESs) are green alternatives for extraction processes, given their low or non-toxicity, biodegradability, and reusability. This review discusses the latest research (in the last two years) employing DESs for phenolic extraction, solvent components, extraction yields, extraction method characteristics, and reviewing the phenolic sources (natural products, by-products, wastes, etc.). This work also analyzes and discusses the most relevant DES-based studies for phenolic extraction from natural sources, their extraction strategies using DESs, their molecular mechanisms, and potential applications.

Development of a colorless Centella asiatica (L.) Urb. extract using a natural deep eutectic solvent (NADES) and microwave-assisted extraction (MAE) optimized by response surface methodology

This study outlines a green process for Centella asiatica (L.) Urb. (CA) extraction. Natural deep eutectic solvents (NADESs) and microwave-assisted extraction (MAE) were combined to provide a high bioactive compound yield and high antioxidant activity. Among the NADESs evaluated, the combination of acetylcholine chloride : malic acid : water (1 : 2 : 2): water (40 : 60) was the best for extraction. These conditions provide high madecassoside (MS) (21.7 mg g-1 dry weight) and asiaticoside (AS) (12.7 mg g-1 dry weight) yields, with greater than 80% (v/v) EtOH (13.3 mg g-1 MS and 7.80 mg g-1 AS). In addition, the extracts from this process showed higher antioxidant activity (IC50 = 0.26 mg mL-1) than the CA aqueous EtOH and water extracts. Moreover, the color of the extract products was less green than that of the extracts prepared using EtOH and aqueous EtOH as solvents, which are suitable for cosmeceutical products. Response surface methodology (RSM) was used for MAE optimization. The ANOVA data from the central composition design (CCD) of RSM were fitted with quadratic models yielding acceptable R 2 (>0.93), adjusted R 2 (>0.87), predicted R 2 (>0.81), and nonsignificant lack of fit (p  > 0.05) values. The quadratic model was validated using optimal conditions (30 s, power 300 W, and a liquid to solid ratio 20 mL g-1), and the model validation showed more than 80% accuracy in both MS and AS yields. This research presented an effective green process for CA extraction, which resulted in an environmentally friendly CA extract requiring little energy consumption and no organic solvents.