Extraction of phenolic compounds from spent coffee ground using natural deep eutectic solvents: New modeling approach

Bitter melon (Momordica charantia) is a rich source of phytochemicals including phenolic compounds with diverse health-promoting benefits and potential food industry application due to their antioxidant potential. Bitter melon leaves have been limitedly investigated in comparison to bitter melon fruits. The current work explores the use of green extraction methodology to optimize enhanced extraction of phenolic compounds from bitter melon leaves using ultrasonically assisted extraction and choline chloride-acetic acid (CHAC)–based natural deep eutectic solvent. Extraction using CHAC significantly improved the extraction of total phenolic compounds, total flavonoids, and individual phenolic compounds (including gallic acid, chlorogenic acid, vanillic acid, epicatechin, and quercetin-3-glucoside) in comparison to water, ethanol, and methanol. The effect of molar ratio, water content, temperature, and time on the extraction efficiency of bitter melon leaf phenolic compounds by CHAC was explored and optimized with surface response methodology (central composite design). The optimum condition for the extraction of individual phenolic compounds is a molar ratio of 1:4.35 CHAC with 20.68% water content at 75 °C for 21.23 min. Evaluation of the bioaccessibility of individual phenolic compounds concluded that the most bioaccessible compound was vanillic acid (105.00 ± 2.52%) followed by salicylic acid, chlorogenic acid, syringic acid, gallic acid, epicatechin, and quercetin-3-glucoside.

The extraction of phenolic compounds with antioxidant activity (AA) of winemaking by-products using response surface methodology and fractional factorial design was investigated. The effects of grape pomace from wine (GWP) and juice production (GJP), temperature, solvent type and time on the extraction of total phenolic compounds (TPC) and AA were evaluated. The TPC and AA varied from 17.91 to 35.10 mg (GAE) g−1 (gallic acid equivalent) and from 65.12 to 149.27 µmol Trolox g−1 of pomace, respectively. For both by-products the optimization suggest that solvent acetone at 60 °C was the best condition. However, the best time for GJP and GWP were 15 min and 45 min, respectively. Gallic acid was the major phenolic compound identified by liquid chromatography in the GJP, followed by coumaric acid, ferulic acid, trans-resveratrol and caffeic acid. The content of anthocyanins for GWP and GJP varied from 640 to 780 mg cyanidin g−1. The responses of the factorial design showed that the GJP had the highest content of TPC and AA when compared to the GWP. Despite superiority of the GJP, these finding supporting the utilization of both grape pomace in food industry due to their high amount of bioactive compounds.

Natural deep eutectic solvents (NADESs), as emerging green solvents, can efficiently extract natural products from natural resources. However, studies on the extraction of phenolic compounds from celtuce (Lactuca sativa var. augustana) leaves (CLs) by NADESs are still lacking. This study screened the NADES L-proline-lactic acid (Pr-LA), combined it with ultrasound-assisted extraction (UAE) to extract phenolic compounds from CLs, and conducted a comparative study on the extraction effect with traditional extraction solvents. Both SEM and FT-IR confirmed that Pr-LA can enhance the degree of fragmentation of cell structures and improve the extraction rate of phenolic compounds. Molecular dynamics simulation results show that Pr-LA can improve the solubility of phenolic compounds and has stronger hydrogen bonds and van der Waals interactions with phenolic compounds. Single-factor and Box-Behnken experiments optimized the process parameters for the extraction of phenolic compounds from CLs. The second-order kinetic model describes the extraction process of phenolic compounds from CLs under optimal process parameters and provides theoretical guidance for actual industrial production. This study not only provides an efficient and green method for extracting phenolic compounds from CLs but also clarifies the mechanism of improved extraction efficiency, which provides a basis for research on the NADES extraction mechanism.

Natural deep eutectic solvents (NADES) have gained significant attention as green solvents due to their unique properties, such as high solubility, low volatility, low toxicity, and tunability. Liquid phase microextraction (LPME) is a sample preparation technique that plays a crucial role in analytical chemistry, and the use of NADES as extraction solvents in LPME offers numerous benefits compared to traditional solvents. NADES can effectively extract bioactive compounds from natural sources without damaging their structure and activity. They can also serve as solvents and catalysts in organic reactions, enhancing the bioavailability of natural compounds. In addition, NADES can be utilized as mobile or stationary phases in chromatographic techniques for separating and analyzing natural compounds. The review highlights the efficiency of NADES in terms of extraction ability, analyte stabilization capacity, and detection compatibility. Moreover, the availability of their components, ease of preparation, low toxicity, cost-effectiveness, and biodegradability make NADES attractive for researchers in the field of analytical chemistry. The applications of NADES in LPME contribute to the principles of green analytical chemistry and green sample preparation by providing a sustainable and environmentally friendly approach to sample preparation. A comprehensive overview of the applications of NADES in liquid phase microextraction is provided, emphasizing their potential for advancing green practices in analytical chemistry.

Choline chloride-based natural deep eutectic solvents for the extraction and stability of phenolic compounds, ascorbic acid, and antioxidant capacity from Citrus sinensis peel

Natural deep eutectic solvents (NDESs) were used to extract flavonoids and polyphenols from lotus (Nelumbo nucifera Gaertn.) leaves at the same time, and the extraction process was optimized to provide reference for the effective development and utilization of lotus leaves. The deep eutectic solvents (DESs) with the highest yield of flavonoids and polyphenols were screened out from 19 different NDES combinations. The response surface method was employed to optimize the extraction process. After a rational design, a lactic acid/glycerol (molar ratio 1:2) DES was chosen as the optimal extraction solvent, and the optimum extraction parameters were as follow: water content (29%), liquid–solid ratio (37:1 mL/g), extraction time (61 min), and extraction temperature (53 °C). Compared with traditional water extraction or ethanol extraction, it improved the yield of flavonoids (126.10 mg/g) and polyphenols (126.10 mg/g). By LC–MS analysis, 19 flavonoids or organic acid compounds with known compound structural formulae were identified in the DES extract of lotus leaves. By comparing the free radical scavenging ability and total reducing ability, the extraction of lotus leaves using the NDES method was superior to both ethanol extraction and water extraction. It is a green, environmentally friendly, and efficient extraction method for antioxidants from leaves of Nelumbo nucifera Gaertn.

In the past decade, natural deep eutectic solvents (NADESs) as green and sustainable extraction solvents with great potential for the efficient extraction of bioactive compounds from the plants are emerging. In this study, a microwave-assisted technology is used to prepare natural deep eutectic solvents. And natural deep eutectic solvents as pretreatment solvents coupled with microwave-assisted hydrodistillation (MAHD) for isolating essential oil (EO) derived from turmeric (Curcuma longa L.) is investigated. To improve the essential oil yield of turmeric (Curcuma longa L.) as a target, various factors affecting extraction efficiency including the type and amount of natural deep eutectic solvents, pretreatment time, pretreatment temperature and hydrodistillation (HD) time are discussed and optimized through central composite design (CCD) of the response surface methodology (RSM). The optimal conditions are as follows: natural deep eutectic solvent composed of choline chloride and oxalic acid (molar ratio with 1:1) as a pretreatment solvent, an amount of 60 g, a pretreatment time of 5 min, a pretreatment temperature of 84 ºC, a hydrodistillation time of 76 min. Under the optimum conditions, the highest essential oil yield of 0.85% is achieved. Additionally, the essential oil is analyzed by using gas chromatography-mass spectrometry (GC-MS), with a total of 49 compounds being identified. Through combining natural deep eutectic solvents with a microwave-assisted hydrodistillation technique, this work provides an eco-friendly extraction way of isolating essential oil, which boosts development in the monitoring other spice quality field.

As sustainability gains prominence, the circular economy has encouraged the valorization of agri-food by-products, which are rich in phenolic compounds known for their antioxidant and anti-inflammatory properties. Conventional extraction methods commonly employ organic solvents, which contradict green chemistry principles. Natural deep eutectic solvents (NaDESs) have emerged as environmentally friendly alternatives for recovering bioactive compounds from food waste. This review investigated recent studies (2020–2024) on ultrasound (UAE), microwave (MAE), and pressurized liquid extraction (PLE) using NaDESs to extract phenolic compounds from agri-food by-products. A total of 116 publications were initially identified, of which 19 met the inclusion criteria. UAE combined with NaDESs proved effective, particularly for fruit and oilseed residues. MAE achieved good yields for phenolic acids and flavonoids but showed limitations on high temperatures. PLE, though less explored, demonstrated promising results when optimized for temperature, pressure, and NaDES composition. The combination of NaDESs with assisted extraction techniques enhanced yield, selectivity, and environmental performance compared to conventional approaches. These findings highlight a greener and more efficient strategy for phenolic recovery within a biorefinery framework. Ultimately, this approach contributes to the sustainable management and valorization of agri-food by-products, supporting circular economy principles and the development of cleaner extraction technologies for functional ingredients.

Sustainable strategies to obtain bioactive compounds from citrus peels by supercritical fluid extraction, ultrasound-assisted extraction, and natural deep eutectic solvents.

Extraction of natural compounds generally uses organic solvents, which have a high risk to human health. Green solvents based on the natural deep eutectic solvents (NADES) have been used for the extraction of active compounds from coffee cherry waste. This research has formulated eight NADES based on choline chloride by combining fructose, citric acid, glycerol, proline, glucose, xylose, propylene glycol, and lactic acid with a mole ratio of 1:2. The FTIR analysis of NADES showed that there was a hydrogen bond interaction with OH group peaks in the wave number range 3012-3357 cm-1. NADES application was used for phenolic and tannin extraction from coffee cherry waste. The extraction efficiency of phenolic was combined of choline chloride with HBD of proline>xylose>glucose>glycerol>lactic acid >fructose>propylene glycol>citric acid. The maximum phenolic content in the extract using choline chloride-proline was 11.81 mg GAE/g. The ability of NADES to extract tannins using choline chloride with the combination of glucose>proline>lactic acid>propylene glycol>glycerol>citric acid> fructose. The maximum tannin content was obtained at 1.58% using NADES based on choline chloride with glucose. NADES has been successfully used as an environmentally friendly to replace organic solvents to extract phenolic and tannin in coffee cherry waste.

Red-fleshed apple cultivars with an enhanced content of polyphenolic compounds have attracted increasing interest due to their promising health benefits. Here, we have analysed the polyphenolic content of young, red-fleshed apples (RFA) and optimised extraction conditions of phenolics by utilising natural deep eutectic solvents (NDES). We also compare the antioxidant, neuroprotective and antimicrobial activities of NDES- and methanol-extracted phenolics from young RFA. High-performance liquid chromatography coupled to high-resolution mass spectrometry (HPLC-HRMS) was used for phenolics identification and quantification. Besides young RFA, ripe red-fleshed, young and ripe white-fleshed apples were analysed, revealing that young RFA possess the highest phenolic content (2078.4 ± 4.0 mg gallic acid equivalent/100 g), and that ripe white-fleshed apples contain the least amount of phenolics (545.0 ± 32.0 mg gallic acid equivalent/100 g). The NDES choline chloride-glycerol containing 40 % w/w H2O gave similar yields at 40 °C as methanol. In addition, the polyphenolics profile, and bioactivities of the NDES extract from young RFA were comparable that of methanol extracts. Altogether, our data show that NDES extracts of young RFA are a promising source of bioactive polyphenolics with potential applications in diverse sectors, e.g., for functional food production, smart material engineering and natural therapies.

Enhanced and green extraction of bioactive compounds from Lippia citriodora by tailor-made natural deep eutectic solvents

This investigation focused on assessing and enhancing ultrasound‐assisted extraction (UAE) using natural deep eutectic solvents (NADES) to extract phenolics and terpenoids from sweet basil leaves. The initial stage involved evaluating the extraction performance of twelve NADES and ethanol. A NADES comprising lactic acid and glucose with a 2 : 1 molar ratio and 20% water content (WC) obtained the highest total phenolic content (TPC) and total terpenoid content (TTC). Single‐factor experiments systematically examined the impact of liquid‐to‐solid ratio (LSR), water content in NADES (WC), ultrasound power, temperature, and exposure time on the extraction yield. Optimization using Box–Behnken Design (BBD) models for the lactic acid and glucose‐based UAE revealed the optimal conditions to be 80 ml/g LSR, 30% water, 300 W, 50°C temperature, and a 15‐minute exposure time. Under these optimized parameters, the extraction achieved the highest TPC and TTC at 69.88 mg GAE/g and 110.71 mg UA/g, respectively. This study presents an environmentally friendly and sustainable extraction protocol for the extraction of phenolic compounds and terpenoids from sweet basil leaves.

Shale instability is a significant problem, accounting for approximately 70% of wellbore challenges during drilling operations. To address this issue, shale inhibitors are commonly added to drilling mud to stabilize the encountered shale formations. Ionic liquids and deep eutectic solvents have been recognized as effective shale inhibitors due to their environmental friendliness and effectiveness. However, despite their advantages, these solutions still lack full environmental sustainability, leading researchers to explore more natural alternatives like Natural Deep Eutectic Solvents (NADES). This study focuses on the synthesis and application of a NADES composed of Potassium Chloride (KCl) and glycerine, aiming to enhance the environmental profile and efficacy of shale inhibitors. The NADES was prepared with a 1:8 molar ratio at a temperature of 60 °C. Characterization analyses, including Fourier Transform Infrared and Thermogravimetric Analysis, confirmed the formation of bonds between –(OH) and Cl− and demonstrated the NADES's thermal stability up to 200 °C. Incorporating 3% NADES into water-based mud, prepared following API 13B-1 standards, resulted in significant improvements in mud rheology. Specifically, the addition of 3% NADES reduced filtrate volume by 14.2% and mud cake thickness by 19.2%. Furthermore, the 3% NADES exhibited remarkable inhibition of clay swelling by 69.23% and demonstrated a shale recovery rate of 58%. When compared with 3% KCl and 3% 1-ethyl-3-methylimidazolium chloride (EMIM-Cl), the NADES-based mud outperformed both in terms of efficacy. These findings were further supported by additional analyses, including d-spacing measurements (XRD), Zeta Potential, Surface tension, and Field Emission Scanning Electron Microscopy. Additionally, the rheological behavior of the NADES-based mud aligned with the Yield Power Law at both 25 °C and 100 °C. The study's findings contribute to the advancement of greener drilling practices and highlight the applicability of KCl-based NADES as a potential drilling fluid additive.

The native fruits of the Cerrado have an interesting composition of bioactive compounds responsible for antioxidant, anti-inflammatory, and antimicrobial activities, with technological potential for functional industries. This study investigated the extraction of bioactive compounds in cagaita and mamacadela fruits, under different conditions, using eutectic solvents based on choline chloride (CC) with citric acid (CA) or tartaric acid (TA), plus ethanol as reference. For a better understanding of the extracts, their antioxidant capacity was assessed by the DPPH•, FRAP, ABTS•+, and total phenolic compounds and flavonoids assays, as well as for color, water activity, and identification of bioactive compounds by mass spectrometry. Additionally, the carotenoid contents were evaluated in the ethanolic extracts. The results showed that ethanol was efficient for the extraction of flavonoids and presented advantages demonstrated in the antioxidant analyses of ABTS•+ and FRAP. However, eutectic solvents stood out in the extraction of phenolic compounds, with yields 14.0 and 4.5 times higher than ethanol for mamacadela and cagaita, respectively. In addition, when compared to cagaita, mamacadela had twice the carotenoid content. Furthermore, the CC:TA solvent was the most efficient, demonstrating, by DI-ESI-MS, 29 phenolic compounds in mamacadela and 27 in cagaita. Therefore, the extracts obtained present potential for use as natural pigments, adding value to the fruits and encouraging their exploration by industries.