Next Article in Journal
Occupant-Detection-Based Individual Control of Four-Way Air Conditioner for Sustainable Building Energy Management
Previous Article in Journal
The Mediating Role of Total Quality Management between Corporate Social Responsibility and Corporate Environmental Performance
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 16
Issue 17
10.3390/su16177403
sustainability-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Recovery of Phenolic Compounds by Deep Eutectic Solvents in Orange By-Products and Spent Coffee Grounds

by
Cristiane Nunes da Silva
1,2,
Rhonyele Maciel da Silva
2,
Ailton Cesar Lemes
2 and
Bernardo Dias Ribeiro
1,2,*
1
Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro 21941-901, Brazil
2
School of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro 21941-901, Brazil
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(17), 7403; https://doi.org/10.3390/su16177403 (registering DOI)
Submission received: 25 June 2024 / Revised: 14 August 2024 / Accepted: 26 August 2024 / Published: 28 August 2024
(This article belongs to the Section Sustainable Food)
Browse Figure
Review Reports Versions Notes

Abstract

:
Orange and coffee grounds by-products, rich in phenolic bioactive compounds, can be used in the food industry as antioxidants, colorants, flavorings and additives, mainly because they are solvents that are easy to prepare, have a lower cost, are thermally stable, biodegradable, renewable, and are considered GRAS (Generally Recognized as Safe). Deep eutectic solvents, which are sustainable and have lower melting points, are effective for extracting these compounds. This study aimed to evaluate the use of deep eutectic solvents (DES) in extracting Total Phenolic Compounds (TPC), from orange by-products and spent coffee grounds. DES formed by citric acid: mannitol (CM-DES), and lactic acid: glucose (LG-DES), were evaluated by varying the following parameters: water content (10–50%), solid–liquid ratio (1:5–1:50 w/w) and temperature (40–50 °C). DES citric acid: mannitol presented the best efficiency in the extraction of TPC under the conditions of 10% water, 80 °C, and solid–liquid ratio 1:10 (w/w) for the orange by-products (1782.92 ± 4.50 mg GAE/L) and 1:15 (w/w) for spent coffee grounds (1620.71 ± 3.72 mg GAE/L). The highest antioxidant activity was observed in the extraction with CM-DES for both by-products in the three methods evaluated: Ferric Reducing Antioxidant Power (FRAP) (1.087 ± 0.004 and 1.071 ± 0.006 mol ascorbic acid/L), DPPH radical scavenging activity (2,2-difenil-1-picrilhidrazil—DPPH) (0.233 ± 0.003 and 0.234 ± 0.001 mol Trolox equivalent/L), and radical cation scavenging activity ABTS (2,2-azino-bis (3-ethyl-benzothiazoline-6-sulfonic acid—ABTS) (0.284 ± 7.16 and 0.319 ± 0.002 mol Trolox equivalent/L). Therefore, DES with citric acid: mannitol is a promising alternative to conventional solvents to recover phenolic compounds in agro-industrial by-products, such as orange by-products and SCG.

1. Introduction

Agribusiness annually generates more than 2 million tons of by-products rich in different bioactive compounds worldwide [1]. Therefore, exploring these by-products becomes an attractive alternative for obtaining compounds with high added value [2]. Brazil is recognized as the world’s largest producer of oranges and coffee, producing 16.9 million tons of oranges and 59.9 million bags of coffee (60 kg) in 2023 [3]. Orange processing generates a large volume of peel, bagasse, and seeds that come mainly from the production of orange juice, representing 50% of the total weight of the fruit, corresponding to approximately more than 8 thousand tons of by-products [4]. These by-products, mainly orange peel, are recognized for the presence of several bioactive compounds, such as phenolic compounds, essential oils, pectin, natural pigments, and dietary fiber [5,6]. Phenolic compounds represented by flavonoids (hesperidin, narirutin, and naringenin) and phenolic acids (caffeic, p-coumaric, and ferulic acid) are the main bioactive compounds of these by-products and are considered an excellent source of phenolic compounds [6,7]. Phenolic compounds are secondary metabolites present in different parts of plants. Citrus by-products show antioxidant properties in reducing lipid and protein oxidation in meat products [8], antimicrobial activity tested in vitro in Staphylococcus aureus and Escherichia coli strains in a functional beverage [9], antifungal activity in peach-based products (Botrytis cinerea, Monilinia fructicola, and Alternaria alternata) [10], and anticancer activity in reducing tumors derived from esophageal cancer stem cells in vivo [11].
In addition, coffee is one of the most consumed drinks in the world, being the second most-sold product worldwide. The large consumption of coffee results in the production of around 20 million by-products that can be generated at different stages of coffee processing [12]. Spent coffee grounds (SCG) are the by-products obtained from soluble coffee industries and during the preparation of the drink in domestic and commercial establishments [12]. Approximately 7 million tons of SCG production annually is estimated worldwide [13]. Despite their low economic value, SCG contain various compounds, including phenolic compounds, caffeine, oil, and polysaccharides [14]. Phenolic compounds stand out for being one of the essential bioactive groups present in SCG, with chlorogenic acids being the most studied phenolic group due to their potential biological properties [14,15,16]. In addition to the presence of other phenolic acids, such as caffeic, coumaric, ferulic, and gallic acid [14,15,16], SCG have been reported to have antioxidant activity in the protection of fish oil and cinnamon oil [17], antibacterial activity against Escherichia coli [18], antifungal activity against skin antifungal agents (Candida krusei and Trichophyton rubrum), anticancer activity in human tumor cells (gastric adenocarcinoma and breast adenocarcinoma) [19], and antiproliferative activity concerning human lung carcinoma cells (A549) [20].
The recovery of biomolecules from plant matrices is obtained through extraction processes, which allows the isolation, identification, and extraction of different constituents, such as phenolic compounds, flavonoids, and carotenoids [21]. These biomolecules have several functionalities of potential interest to the food, pharmaceutical, and cosmetic industries [22]. Different extraction methods, such as Soxhlet, extraction solvent, and maceration, are commonly used to obtain these biomolecules [21]. However, these methods have some disadvantages, such as a long process time, the use of large amounts of toxic and flammable solvents, and some methods that require high temperatures, making them unsuitable for heat-sensitive substances, such as phenolic compounds [22]. Therefore, it is essential to implement more sustainable and ecological extraction processes to reduce the generation of toxic waste.
Deep eutectic solvents (DES) are green solvents with several advantages that encourage their use in various areas of chemistry, including the extraction of bioactive compounds from plant matrices [23]. DES are formed by combining hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs), resulting in a mixture that has a lower melting point than its components [24]. HBAs and HBDs can be combined to obtain more effective solvents from renewable precursors from natural sources, such as sugars, organic acids, polyalcohols, and amino acids [25]. DES have advantages such as biodegradability, biocompatibility, recyclability, easy preparation, lower cost, low volatility, and lower toxicity than organic solvents [26,27]. However, combining some HBAs and HBDs can lead to DES with high viscosity, making their use difficult. Moreover, adding water can facilitate the use of DES due to viscosity modulation and directly influencing extraction selectivity [27]. The selection of available and safe solvents is essential for the food and pharmaceutical industries. Citric acid, lactic acid, mannitol, and glucose are components of our diet and provide additional benefits to human health. These components are considered GRAS (Generally Recognized as Safe). Therefore, they are more ecological, safer, and highly available alternatives for application in the food and pharmaceutical industries.
DES have already been applied in the recovery of phenolic compounds from different plant matrices, which include blueberry by-products [28], passion fruit peel [29], peanut leaves and stems [30], apple pomace [31], avocado peel [32], and date seeds [33]. Therefore, this study aimed to evaluate the effect of DES (citric acid: mannitol and lactic acid: glucose) on the extraction of total phenolic compounds from orange by-products and SCG. The impact of different water content (10–50% w/v), solid–liquid ratio (1:5–1:50 w/w), and temperature (40–80 °C) were tested to maximize the yield of total phenolic compounds and antioxidant activity of orange by-products and SCG. These conditions were evaluated to increase intermolecular interactions and hydrogen bond formation, responsible for raising the dissolution and extraction of phenolic compounds in DES and, consequently, improving the recovery and bioactivity of these bioactive compounds. To compare the results, a conventional extraction was performed using methanol and water (80%:20% v/v) under the same process conditions.

2. Materials and Methods

2.1. Preparation of Raw Material

Orange by-products and SCG were used to carry out the experiments. The company Cutrale®, located in São Paulo—SP, Brazil, donated the orange by-products. The by-product, composed of dried bark, seeds, pomace, and leaves, was ground in knife mills (Tecnal R-TE-680, Piracicaba, Brazil) and sieved to reach a particle size of ≤0.465 nm. The SCG were acquired from commercial establishments in Rio de Janeiro—RJ, Brazil. Subsequently, this by-product was dried in an oven (Tedesco FTT 150 G, Caxias do Sul, Brazil) at 50 °C for 48 h. The moisture and particle size diameter were set to 5–6% (w/v) and ≤0.465 mm, respectively. The orange by-product and SCG were packaged in polyethylene packaging and stored under refrigeration (<10 °C) and protected from light until analysis.

2.2. Characterization of Orange By-Products and Spent Coffee Grounds

The physicochemical composition of orange by-products and SCG were evaluated according to the AOAC [34] analytical standards, with some modifications. Moisture was determined by drying the by-products in an oven at 105 °C until they reached a constant weight. The ash content was quantified by incineration at 550 °C and the total protein content was quantified by the Kjeldahl method, considering 6.25 as a correction factor. The total lipids were determined by Soxhlet extraction with petroleum ether. Therefore, carbohydrates were determined by the difference from the other components (100–% moisture–% lipids–% protein–% ash). The caloric value was determined according to general conversion factors: total caloric value (kcal/100 g) = (% proteins × 4 kcal/g) + (% lipids × 9 kcal/g) + (% carbohydrates × 4 kcal/g) [35]. All analyses were performed in triplicate.

2.3. Preparation of Deep Eutectic Solvents (DES)

The DES used to extract phenolic compounds were prepared as Ribeiro, et al. [36] described. Two DES were prepared from citric acid + mannitol (CM-DES) in a molar ratio of 1:1 and lactic acid + glucose (LG-DES) in a molar ratio of 5:1 (w/w). Subsequently, the mixture of components was heated at 80 °C (Ika C-Mag HS 4, Campinas, Brazil), under constant stirring until complete homogenization of the liquid occurred. The temperature was continuously monitored. Afterward, the solvents were stored at room temperature (25 °C).

2.4. Extraction of Phenolic Compounds by Deep Eutectic Solvents

The extraction of total phenolic compounds (TPC) from orange by-product and SCG using deep eutectic solvents was carried out by evaluating the following process parameters: water content (%), solid–liquid ratio (w/w), and temperature (°C) in the yield of total phenolic compounds and antioxidant activity. For comparison purposes, TPC was extracted with methanol and water (MeOH-80%:20% v/v) for 2 h at 60 °C, with a stirring speed of 1000 rpm using Thermomixer equipment (Thermomixer C, Eppendorf, Hamburg, Germany) [37]. The pH of the system (sample + solvent) was evaluated using a pH meter (Tecnal) before and after the extraction process. The content of TPC was also monitored throughout the extraction process.

2.4.1. Determination of the Effect of Water Content

Initially, 100 mg of sample (orange by-product and SCG) were weighed and solubilized in 1000 mg of DES (citric acid: mannitol (CM-DES) and lactic acid: glucose (LG-DES)) separately in a solid–liquid container with the ratio of 1:10 (w/w). Different water content was added to evaluate the effect of water on the extraction of phenolic compounds (10%, 20%, 30%, 40%, and 50% (v/v)). The water content range was determined based on the solubilization capacity of the matrix (by-products) in the solvent, with adequate viscosity for its operation and extraction of phenolic compounds. Then, the samples were extracted for 2 h, at 60 °C and 1000 rpm, using the Thermomixer equipment (Thermomixer C). The supernatant was collected after centrifugation (5804 R Centrifuge) for 15 min at 10,000 rpm. Subsequently, the samples were stored (−18 °C) until further analysis.

2.4.2. Determination of the Effect of Solid–Liquid Ratio

After studying the best water content to extract TPC using DES, this parameter was fixed and the effect of the solid–liquid ratio was also evaluated, with variations of 1:5, 1:15, 1:20, 1:30, 1:40, and 1:50 (w/w). The samples were subjected to extraction (2 h, 60 °C, 1000 rpm). Phase separation was performed by centrifugation for 15 min at 10.000 rpm (Eppendorf Centrifuge 5804 R), and the supernatant was collected. Afterward, the samples were frozen (−18 °C) and kept away from light until further analysis.

2.4.3. Determination of the Effect of Temperature

To evaluate the effect of temperature, the samples (orange by-product and SCG) were subjected to different temperatures (40, 50, 70, and 80 °C) for 2 h at 1000 rpm, and the water content and solid–liquid ratio were determined in the previous sections (Section 2.4.2 and Section 2.4.1, respectively). Afterward, the samples were centrifuged, and the supernatant was stored frozen (–18 °C) and kept away from light until further analysis.

2.5. Total Phenolic Compounds (TPC)

Total phenolic compounds (TPC) were determined according to the methodology proposed by Almeida et al. [38], with some modifications. The analysis was carried out in 96-well microplates, using a mixture of 10 µL of the sample (1:6 v/v) and 200 µL of Folin-Ciocalteau reagent (1:10 v/v). After 3 min, the reaction was stopped with the addition of 100 µL of sodium carbonate (20% w/v). Absorbance was measured at 765 nm with a spectrophotometer (Spectramax M2, San Jose, CA, USA). The standard curve was performed with gallic acid; the results were expressed in mg gallic acid/L of the sample (mg GAE/L).

2.6. Determination of Antioxidant Activity

Antioxidant activity was determined using ABTS radical cation scavenging activity, DPPH radical scavenging activity, and Ferric Reducing Antioxidant Power (FRAP) methodology. The antioxidant activity using the ABTS method was carried out using the method proposed by Re et al. [39], with some modifications [40]. The ABTS method was carried out by reacting 5 mL aqueous ABTS solution (7 mM) and 88 μL potassium persulfate solution (140 mM) to produce the ABTS radical cation (ABTS+), and this was kept in the dark for 16 h. The ABTS radical was diluted with ethanol to obtain an absorbance of 0.7 ± 0.05 at 734 nm. In the dark, 15 μL of the samples were added to 1500 μL of ABTS radical solution, and after 6 min the absorbance at 734 nm (Spectramax M2) was measured. The results were expressed in mol of Trolox equivalents per liter of the sample (mol of Trolox equivalents/L). Antioxidant activity was also determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical method, proposed by Rufino et al. [41], with some modifications. 45 µL of the sample and 1800 µL of the DPPH solution were added, and after 40 min (in the dark), the absorbance was measured at 515 nm in the spectrophotometer (Spectramax M2). The results were expressed in mol of Trolox equivalents per liter of sample (mol of Trolox equivalents/L). The FRAP method was carried out by preparing the FRAP reagent (1 mL of TPTZ 10 mM, 1 mL of FeCl3 20 mM, and 10 mL acetate buffer 300 mM pH 3.6) in the dark. The reaction was performed by mixing 15 μL of the sample with 285 μL of the FRAP reagent. After 30 min of incubation in the dark the absorbance was measured at 593 nm, and the results were expressed in mol of ascorbic acid equivalent [42].

2.7. Statistical Analysis

All analyses were performed in triplicate, and results were presented as mean values ± standard deviation. The average values of all experiments were evaluated using analysis of variance (ANOVA) and the Tukey mean test at a 5% significance level (p ≤ 0.05), with the Statistica (version 8.0, StatSoft, Tulsa, OK, USA). The results for both by-products were submitted to t-test (version 8.0, StatSoft) to evaluate the best DES in extracting phenolic compounds.

3. Results and Discussion

3.1. Physicochemical Composition of Orange By-Products and SCG

Proteins and lipids are macronutrients that can be extracted from agro-industrial byproducts and transformed into high-value-added ingredients for the food industry. Proteins are macromolecules made up of one or more chains of amino acids joined by peptide bonds, which have techno-functional properties that allow their application in the food industry as gelling agents, emulsifiers, binding agents, foam formation, solubility, thermal stability, and antioxidants [43,44,45]. Lipids are molecules insoluble in water but soluble in organic compounds. Lipids extracted from orange by-products can be applied as potential natural antioxidants in food products to inhibit lipid oxidation and increase shelf life, flavoring, and antimicrobials [46,47]. SCG lipids can be used as a fat substitute, as natural antioxidants (tocopherols), and in the formulation of nutraceutical products (fatty acids) [47,48].
Table 1 presents the physicochemical composition of orange by-products and SCG. Orange by-products and SCG are agro-industrial by-products with high total carbohydrate content, 77.67 ± 0.09% and 74.31 ± 0.67%, respectively. Orange by-products and SCG are rich in cellulose, hemicellulose, and sugars such as mannose, galactose, glucose, and arabinose [49,50]. Furthermore, orange by-products are sources of pectin, and SCG contain high concentrations of galactomannans, which have different technological properties and can be applied in the formulation of various food products in terms of stabilizers, thickeners, texturizers, gelling capacity, and fermentability [49,51]. Other studies in the literature report the physical–chemical composition of orange by-products and SCG; however, there is significant variability in the results. This variability is attributed to the different species of orange and coffee, growing conditions, soil types, climatic conditions, processing (kind of fermentation and degree of coffee roasting), types of extraction methods applied, and coffee beverage preparation techniques [16,52]. In addition, it is worth noting that there may be a difference in the proportionality of the material between peel, leaf, bagasse, and seeds, that is, of all the fragmented material, due to the process used for extraction, which is not always reported in the studies described in the literature. Afrin et al. [53] reported 86.26 ± 0.36% to 87.05 ± 0.43% total carbohydrates for orange by-products. Other studies have reported 24.09 ± 1.51% to 38.10 ± 0.50% for SCG [16,54]. Therefore, orange by-products and SCG are promising sources for extracting high-value compounds with potential applications in the food industry. Afrin, Acharjee and Sit [53] reported a range of 86.26 ± 0.36% to 87.05 ± 0.43% total carbohydrates for orange by-products. Other studies have reported 24.09 ± 1.51% to 38.10 ± 0.50% for SCG [16,54].
SCG had an initial moisture content of 75.15 ± 1.85%, corroborating other studies that reported that SCG have a high moisture content. The dry SCG presented 4.91 ± 0.35% moisture. The low moisture content is essential to reduce chemical degradation reactions and microbial growth. Orange by-products had a lower protein (6.93 ± 0.00%), lipid (2.39 ± 0.10%), and ash (5.75 ± 0.01%) content than reported by Huang and Ma [55], who reported a percentage of 10.38 ± 0.15% of proteins, 3.23 ± 0.21% of lipids, and 3.12 ± 0.01% of ash. Regarding protein content, SCG presented a significant content of this macronutrient. The result of the present study is within the range reported in other studies of SCG with values of 12.83 ± 0.15% to 17.44 ± 0.44% [56,57]. Similar behavior was observed for lipids from 2.29 ± 0.30% to 13.70 ± 0.12% and ash from 1.40 ± 0.18% to 3.40 ± 0.30% [16,57,58]. The orange by-products (359.89 kcal/100 g) and SCG (405.23 kcal/100 g) had high caloric values. A similar result was reported for SCG with 411.00 kcal/100 g [49], whereas a lower calorie content was reported for orange by-products with 195.98 kcal/100 g [59].
In addition to macronutrients, bioactive compounds such as phenolic compounds, were also present and reported in significant quantities in orange by-products and SCG. Phenolic compounds are biologically active compounds present in small amounts in plants [51]. The particular interest in these bioactive compounds is related to their antioxidant activity, which can delay or inhibit the production of reactive species and oxidation reactions of macromolecules, such as proteins and lipids, as well as their antimicrobial activity, which inhibits microbial growth [51]. The orange by-products and SCG presented a total phenolic compound content of 427.79 ± 6.46 mg GAE/L (4.28 ± 0.06 mg GAE/g), and 579.20 ± 5.75 mg GAE/L (5.79 ± 0.05 mg GAE/g) obtained by the conventional method using an MeOH solution (80% v/v). These values agree with those found in other studies of 4.60 to 5.27 mg GAE/g for orange by-products [60,61,62]; and 4.89 to 16.2 mg GAE/g for SCG [16,63,64], using conventional solvents, such as methanol and ethanol, or aqueous mixtures of these solvents. Therefore, extracts rich in phenolic compounds can be applied in the formulation of food products as ingredients or food additives and in the production of bioactive packaging, with the aim of obtaining products rich in natural antioxidants, that are safe and that have a longer shelf life. In addition, their biological effects such as neuroprotective, cardioprotective, anti-aging, anticancer, and anti-inflammatory ones, allow their application in the production of medicines and products in the cosmetic area [65,66].

3.2. Extraction of Phenolic Compounds Using DES

3.2.1. Effect of Water Content on TPC Extraction

The great interest in DES is related to their advantages that allow the combination of renewable, biocompatible, and biodegradable components due to lower toxicity, volatility, and flammability [67]. The selection of safe and available solvents is essential when the target is application in the food industry. In addition to the advantages in performance, the components used to form DES were citric acid, mannitol, lactic acid, and glucose, which are compounds that, in addition to being part of our diet, provide positive effects on human health [68]. Citric acid is an organic acid derived from citrus fruits, widely used as a natural preservative due to its antioxidant and acidifying properties. Lactic acid is obtained from the natural fermentation process of products, such as cheeses and yogurts, and through the human body during daily physical activity [68]. In the food industry, it is widely used as an acidifier and acidity regulator, as well as in dairy products. Glucose is a monosaccharide that has several applications in the food industry, such as flavor enhancer and sweetener, and it is also used by the body as a source of energy. Mannitol is a naturally occurring sugar alcohol (polyalcohol) found in fruits and vegetables [69]. Its applications in the food industry include stabilizers, texture formation, and as a sugar substitute in the formulation of food products [69,70]. Furthermore, mannitol has biological properties that positively impact human health by eliminating reactive oxygen species [70]. Therefore, they are more ecological alternatives for application in the food industry.
Notably, DES can be regenerated and reused in new extraction processes. DES can be regenerated using different recovery processes, such as antisolvent addition (water, acetone, and ethanol), crystallization agents, membrane filtration, solid–liquid extraction (using a macroporous resin), liquid–liquid extraction, supercritical fluid extraction, and separation by density and viscosity. However, processes using an antisolvent, solid–liquid extraction using macroporous resins, and combinations of methods (addition of antisolvent plus membrane filtration) allow the recovery of over 90% of DES [71]. These DES can be used again for new extraction processes of bioactive compounds from plant matrices, providing a more sustainable, economical process with less waste generation.
Different contents of water (10–50% v/v) were added to different deep eutectic solvents defined as CM-DES, which were composed of citric acid, mannitol, and LG-DES, consisting of lactic acid: glucose, to evaluate the effect of this parameter on extraction efficiency. The MeOH solution (80% v/v) was the standard conventional method to extract the phenolic compounds in orange by-products and SCG. The TPC of orange by-products and SCG were dependent on the type of DES used and the water content, with a significant effect (p ≤ 0.05) on the extraction of TPC. As shown in Table 2, the best results were obtained by adding 10% of water with 786.70 ± 2.26 (CM-DES) and 596.26 ± 1.51 (LG-DES) mg GAE/L for orange by-products, and 756.70 ± 8.57 (CM-DES) and 612.78 ± 4.52 (LG-DES) mg GAE/L for SCG. These results demonstrate that adding 10% of water to CM-DES and LG-DES results in greater efficiency in the extraction of TPC from orange by-products and SCG. Water plays an essential role in the extraction process. Most DES have a high viscosity, which limits mass transfer and extraction performance. The addition of water leads to a reduction in DES viscosity, enhancing mass transfer and consequently improving extraction efficiency [72]. Furthermore, the addition of water favors the change in the polarity of DES, affecting the dissolution capacity of the target compound, according to the principle of like dissolves like. It allows an increase in the solubility of DES due to the ability to form hydrogen bonds with the target compounds (Figure 1) [72,73]. These results were superior to those obtained by the conventional extraction method using MeOH (80% v/v) solution, mainly for CM-DES, 50% and 20% higher for orange by-products and SCG, respectively, supporting DES as a promising alternative to traditional solvents.
Organic solvents are typically used to extract TPCs from plant matrices. The action mechanism involves the solvent’s penetration into the matrix and the solubilization of the target compounds in the solvent. The main TPCs are constituents of a polar nature due to the presence of OH and =O groups in their chemical structure [74]. In turn, organic solvents such as methanol and ethanol are polar compounds, which allow the dissolution of compounds with a similar polarity, such as TPC [74]. However, mixing organic solvents with water can enhance extraction performance by increasing the polarity of the solvents, resulting in increased solubility of the target compound, better mass transfer, and consequently, greater efficiency in the extraction process [75]. However, the disadvantages of these solvents, such as large volumes, toxicity, flammability, and volatility, make it essential to search for more ecological and sustainable solvents such as DES [22].
The water content significantly affects DES’ viscosity, modifying their physical and chemical characteristics [76]. According to Gómez et al. [77] DES formed by mixtures of organic acids and sugars results in solvents with high viscosity, such as citric acid and fructose (115,039.0 mPa.s), and citric acid and glucose (437,768.5 mPa.s), hindering extraction efficiency. The authors observed that the addition of 10–50% water in DES promoted a reduction of 1384.8 mPa.s and 5.8 mPa.s in the viscosity of DES formed by citric acid and fructose, and 3006.2 mPa.s and 5.9 mPa.s in the viscosity of DES formed by citric acid and glucose. Therefore, adding water is an alternative to reduce the viscosity of DES and improve the extraction of target compounds.
By adding 10% water, the viscosity of these solvents can be reduced by breaking the hydrogen bonds formed between the constituents of the eutectic mixture, favoring better extraction efficiency by maximizing the extraction of phenolic compounds [76]. Furthermore, adding water can change the solvent’s polarity, increasing the DES’ polarity and, consequently, the TPC extraction rate [31]. The increase in TPC was observed with the addition of up to 10% of water, but at a content of 20% to 50%, there was a lower efficiency in TPC recovery. Excess water, that is, the addition of water content above 10%, can weaken the formation of hydrogen bonds between DES and TPC, resulting in lower solubility and, consequently, lower mass transfer rate and efficiency in extraction [31]. Therefore, water content is a factor that must be considered to achieve better recovery in the extraction of TPC.
However, despite a significant decrease (p ≤ 0.05) occurring with increasing water content, the addition of 20–40% provided TPC levels higher than those obtained by MeOH (80% v/v) for orange by-products using CM-DES (acid citric: mannitol). These results showed that CM-DES, adding up to 40% water, provides a better TPC extraction rate than the conventional method (MeOH 80% v/v), which still presents more advantageous options and conditions than the traditional method. When evaluating extraction efficiency between the DES used, CM-DES (citric acid: mannitol) provided better extraction of TPCs compared to LG-DES (lactic acid: glucose) for orange by-products and SCG. DES interact with the phenolic molecule through In Proceedings of the by CM-DES and LG-DES. Therefore, the 10% water content was selected to achieve the best extraction yield of TPC by-products per DES.
Ozturk, Parkinson and Gonzalez-Miquel [74] observed higher yields in the extraction of TPC from orange peel with the addition of 10% water in DES and lower yields in the extraction of TPC with the addition of 50% water. Xu, Ran, Chen, Fan, Ren and Yi [73] observed an increase in the extraction of TPC from citrus fruit peels, with a water content of 20% in DES. Regarding the SCG, Tzani et al. [78] reported higher yields in TPC extraction by adding 25% water to NADES. Fanali et al. [79] found that using water contents above 30% resulted in lower efficiency in TPC recovery from SCG. Other studies have found that the addition of up to 30% water results in better performance in the extraction of TPCs in different plant matrices, such as roses (Rosa Damascene Mill) [80], apple pomace [31], and mulberry leaves [81]. Therefore, adding up to 30% water to DES provides better yield in the extraction of TPCs.

3.2.2. Effect of Solid–Liquid Ratio on TPC Extraction

Seven different solvent ratios were studied to evaluate the effect of the solid–liquid ratio on the extraction of TPC from orange by-products and SCG (1:5, 1:10, 1:15, 1:20, 1:30, 1:40, and 1:50 w/w). At the same time, the other parameters remained constant (10% of water content, 60 °C, and 2 h). The results in Table 3 show that the solid–liquid ratio 1:10 (w/w) of DES (CM-DES and LG-DES) presented better efficiency in extracting TPC from orange by-products with values of 1582.42 ± 2.42 mg GAE/L. In contrast, for SCG, the best yields were obtained with DES (CM-DES and LG-DES) at a solid–liquid ratio of 1:15 of 1568.61 ± 8.95 mg GAE/L. An increase was observed in TPC yield in the solid–liquid ratio from 1:5 (862.43 ± 6.80 mg GAE/L (CM-DES) and 743.42 ± 7.64 mg GAE/L for (LG-DES) to 1:10 (1582.42 ± 2.42 mg GAE/L (CM-DES) and 1192.52 ± 1.51 mg GAE/L (LG-DES) for orange by-products. For SCG, this increase was observed in the solid–liquid ratio from 1:5 (1363.74 ± 2.56 mg GAE/L (CM-DES) and 1074.25 ± 5.00 mg GAE/L (LG-DES) to 1:15 (1568.61 ± 8.95 mg GAE/L (CM-DES) and 1305.24 ± 1.45 mg GAE/L (LG-DES). The solid–liquid ratio is a crucial parameter in the extraction of phenolic compounds, as it directly influences the efficiency of the process. This increase in the extraction rate can be attributed to the concentration gradient between the solvent and the solute, resulting in a higher transfer rate of TPC from the interior of the matrix to the solvent and, consequently, a greater extraction yield [31].
Increasing the solvent concentration favors interactions between the solute and the solvent, increasing the extraction rate until solvent saturation [31]. Therefore, an adequate solid–liquid ratio facilitates the diffusion of phenolic compounds from the solute to the solvent. Furthermore, with a greater amount of solvent, the solubilization of the compounds is more efficient, since the concentration gradient is greater, promoting mass transfer. However, in this study, it was observed that a liquid–solid ratio of less than 1:15 (w/w) produces higher amounts of TPC for orange by-products of 1582.42 ± 2.42 mg GAE/L for CM-DES and 1192.52 ± 1.51 mg GAE/L for LG-DES while for SCG it yields 1568.61 ± 8.95 mg GAE/L for CM-DES and 1305.24 ± 1.45 mg GAE/L for LG-DES. It indicated the excellent efficiency of DES, even at lower concentrations. A similar result was reported by Ozturk, Parkinson and Gonzalez-Miquel [74], who obtained a higher TPC content in orange peel using DES based on choline chloride and ethylene glycol 1:4, in a solid–liquid ratio 1:10 (w/w), 10% water, 60 °C, and 100 min.
The increase in the DES ratio from 1:10 to 1:50 (w/w) for orange by-products and from 1:15 to 1:50 (w/w) for SCG resulted in a significant decrease (p ≤ 0.05), with no enhancing effect on TPC extraction. This demonstrates that obtaining a high yield in the extraction of TPC without needing to add large volumes of solvents makes it advantageous by facilitating the purification of the extract and lowering the extraction cost [31]. The lower yields may be related to the fact that the extraction reached equilibrium, not increasing the yield even with an increase in the proportion of solvent [74]. Furthermore, continuous extraction of TPC results in solvent saturation, leading to less extraction [31]. CM-DES (citric acid: mannitol) provided better efficiency in extracting TPCs when compared to LG-DES (lactic acid: glucose) in the different solid–liquid proportions studied. The results showed that the solid–liquid ratio of 1:10 (w/w) provided better yield in extracting TPC from orange by-products and the solid–liquid ratio of 1:15 (w/w) for SCG. These proportions were selected as fixed for further studies.

3.2.3. Effect of Temperature on TPC Extraction

The effect of different temperatures (40 °C, 50 °C, 60 °C, 70 °C, and 80 °C) on the efficiency of TPC extraction by DES was evaluated. In Table 4, it shows that the TPC yield increased with increasing temperatures. The highest TPC yields were obtained at the maximum studied temperature of 80 °C. Orange by-products obtained 1782.92 ± 4.50 mg GAE/L, and 1582.91 ± 3.85 mg GAE/L for CM-DES and LG-DES, respectively. SCG obtained 1620.71 ± 3.72 mg GAE/L, and 1512.61 ± 8.44 mg GAE/L for CM-DES and LG-DES, respectively, whereas the lowest yields were observed at 40 °C. Orange by-products obtained 1476.81 ± 2.6 mg GAE/L, and 1114.11 ± 2.63 mg GAE/L for CM-DES and LG-DES, respectively. SCG obtained 1372.15 ± 6.65 mg GAE/L, and 1014.60 ± 5.51 mg GAE/L for CM-DES and LG-DES, respectively.
Some DES have a high viscosity that can negatively influence extraction performance due to the lower mass transfer rate and recovery of target compounds. This high viscosity and lower ionic mobility are associated with the presence of a hydrogen bond network, electrostatic and van der Waals forces between the hydrogen bond acceptor and the hydrogen bond donor [52]. The higher yields obtained at higher temperatures (80 °C) may be associated with the fact that the temperature reduces the viscosity due to the weakening of the hydrogen bond networks formed between the components, reducing the surface tension and increasing the solubility of TPC to DES, the effective diffusivity, and extraction efficiency [82,83].
Furthermore, the increase in TPC with increasing temperature may be related to polarity, as temperature can also affect the polarity of DES. Polarity results from combining specific components used to form the solvent [22]. Increasing temperature tends to reduce the polarity of DES, strongly influencing extraction performance [84]. This occurs because the temperature can modulate the polarity of the DES, aligning the eutectic mixture’s polarity with the solute’s polarity, thus favoring an increase in solubility and extraction yield [84]. This process can improve extraction time and facilitate the transfer of TPCs to solvents (DES) [73]. Xu, Ran, Chen, Fan, Ren and Yi [73] observed that temperatures above 50 °C did not improve the yield of TPC extraction by DES from citrus fruit peel because some phenolic compounds are sensitive to high temperatures and can be degraded.
CM-DES was the solvent that enabled the best extraction of TPC from orange by-products and SCG in all evaluated parameters (water content, solid–liquid ratio, and temperature). CM-DES is a eutectic mixture of citric acid and mannitol in a 1:1 ratio. Citric acid is characterized by a low pH (~2.5) and high acidity, while mannitol is a polyalcohol (sugar). Citric acid is an organic acid with a tricarboxylic hydroxyl acid, which has a greater number of −COOH groups compared to lactic acid, which has a monocarboxylic hydroxyl acid [85]. Thus, citric acid has more opportunities to form hydrogen bonds with target compounds [85]. Furthermore, the best results obtained by CM-DES may be related to the fact that the acidic nature of DES influences the extraction performance due to the influence on hydrogen bonds formed between the matrix and the solvent (Figure 1) [73]. According to Gómez-Urios, Viñas-Ospino, Puchades-Colera, Blesa, López-Malo, Frígola and Esteve [68], DES based on organic acids are more polar and acidic. Therefore, they result in a more excellent yield of TPCs due to their ability to form hydrogen bonds with TPCs, increasing the dissolution capacity of these target compounds in DES. Furthermore, DES formed by acids have free H+, which can cause the hydrolysis of polysaccharides, such as cellulose, hemicellulose, and pectin, resulting in increased mass transfer and diffusion of TPC from the matrix to the solvent [86,87]. Therefore, the combination of citric acid and mannitol showed a greater affinity with TPC and consequently allowed greater solubilization and release of these bioactive present in the cell wall of orange by-products and SCG.
The high content of phenolic compounds found in the by-products studied using citric acid and mannitol under the best processing conditions may be associated with the presence of flavanones, represented by hesperidin, narirutin, naringenin, and naringin, and other phenolic compounds, such as caffeic acid, p-coumaric acid, ferulic, gallic, catechin, and epicatechin for orange by-products [6,7]. SCG are related to chlorogenic acid, caffeic acid, ferulic, p-coumaric, and synaptic acid. These phenolic compounds are responsible for the potent antioxidant activity of these by-products [14,15,16].
However, the extraction with LG-DES, formed by the mixture of lactic acid and glucose, presented lower results than those obtained in the extraction by CM-DES (citric acid: mannitol), demonstrating that LG-DES had a lower efficiency in mass transfer and the yield of TPC compared to CM-DES. This result may be related to the lower affinity of LG-DES with TPC, influencing the extraction yield. However, it is worth highlighting that although LG-DES did not provide as significant a yield in TPC extraction as CM-DES, the results obtained were superior to those found for the conventional method, using 80% MeOH, showing that DES is more promising in the extraction of TPC from orange by-products and SCG compared to the traditional methods commonly used for the extraction of TPC.
However, studies have reported that increasing the temperature can result in the degradation of phenolic compounds due to the sensitivity of these bioactive compounds to high temperatures [31,73]. In the present study, the highest results were obtained at the maximum temperature studied (80 °C), with an increase in TPC as the extraction temperature increased, which may be related to higher temperatures favoring a more significant reduction in the viscosity of the DES studied, allowing more excellent mass transfer and better extraction efficiency. In addition, the higher the temperature, the greater the energy expenditure and probability of degradation of other bioactive compounds present in the by-products. Therefore, the use of 80 °C was the ideal temperature to obtain the maximum yield of phenolic compounds in the orange by-products and SCG. Furthermore, studies suggest that DES can increase the stability of phenolic compounds due to intermolecular interactions, especially the formation of hydrogen bonds between DES and target compounds [68,88,89]. The strong hydrogen bond formed between extracts and DES promotes better thermal stability when compared to conventional solvents [68,88,89]. However, further studies are needed to investigate the effect of DES on the stability of bioactive compounds in plant matrices.

3.3. Antioxidant Activity

Antioxidants are abundant components in plant matrices known to delay/inhibit the oxidative reactions of biomolecules caused by reactive species [90]. No single method for determining antioxidant activity evaluates the effect of all antioxidants present in a matrix that makes up different types of bioactive compounds [68]. Therefore, it is necessary to select more than one method to determine antioxidant activity due to the various mechanisms of action of antioxidant agents, origin of antioxidant compounds, and reactive species [68].
This study used three methods (ABTS, DPPH, and FRAP) to evaluate the antioxidant activity of orange by-products and SCG. The antioxidant activity was determined only for the optimal conditions of TPC extraction from orange by-products and SCG using CM-DES (citric acid: mannitol) and LG-DES (lactic acid: glucose) (Table 5). The extracts from orange by-products and SCG using CM-DES had higher antioxidant activity than LG-DES for the three methods evaluated. These results agree with the higher yields obtained for the extraction of TPC since CM-DES was the solvent that provided greater efficiency in the recovery of TPC from orange by-products and SCG. TPCs are recognized as bioactive molecules with high antioxidant activity and are being highly studied due to their biological properties, which are associated with several health benefits [91,92,93].
Furthermore, the increase in antioxidant activity may be related to the fact that DES increase electron transfer and neutralize oxidative reactions [88,94]. This is due to the ability of DES to increase the stability of phenolic compounds during the extraction process, due to the existence of intermolecular interactions, mainly the formation of hydrogen bonds between DES and the target compounds [85,88,89]. These intermolecular interactions can reduce oxidative degradation by reducing the movement of target compounds and the contact of oxygen on the DES surface and air, providing stability and protection to target compounds [94,95]. Lee et al. [96] observed that DES based on betaine and glycerol provided greater stability to the phenolic compounds from kale residues compared to ethanol extraction. It is worth mentioning that extracts rich in phenolic compounds can be used in the formulation of food, cosmetic, and pharmaceutical products since they are extracts rich in antioxidant activity with positive effects on health.
The different antioxidant activity values obtained for the three methods studied, namely ABTS, DPPH, and FRAP, can be attributed to differences in the mechanisms of action between the methods, which allow the identification of different antioxidant compounds. FRAP is a simple method that measures the ability of samples to donate electrons to reduce the ferric ion complex (Fe3+) into the ferrous form (Fe2+) with an intense blue color at acidic pH (pH 3.6) [7]. The acidic environment allows the solubility of iron ions and favors better electron transfer. The ABTS method is based on the ability of antioxidants to neutralize the ABTS radical (2,2′-azinobis (3-ethylbenzenethiazoline6-sulfonic acid), and this has solubility in water and organic solvents, allowing the detection of lipophilic and hydrophilic antioxidant compounds in a wide pH range. The DPPH method consists of neutralizing the DPPH radical (1,1-diphenyl-2-picrylhydrazyl) in the last electronic layer, making the molecules stable and unavailable for the formation of chain oxidation reactions [7].

4. Conclusions

This work demonstrates the feasibility of applying DES (citric acid: mannitol and lactic acid: glucose) to recover phenolic compounds with greater antioxidant activity from orange by-products and SCG. DES based on citric acid and mannitol provided better TPC extraction and greater antioxidant activity from orange by-products and SCG. The optimal conditions for TPC extraction were with DES based on citric acid and mannitol, 10% water, 80 °C, and a solid–liquid ratio of 1:10 (w/w) for orange by-products and 1:15 mg for SCG. In addition to providing good yields in the extraction of TPC, there is the possibility of recovering phenolics from DES in different ways, but as the DES studied are GRAS (Generally Recognized as Safe) and come from natural sources, there is no need to separate TPC from DES, with them remaining active in the extract and being able to be incorporated into the formulation of new products in the food industry. Therefore, DES are a promising alternative for the recovery of high-value compounds with potential antioxidant activity from agro-industrial by-products.

Author Contributions

Conceptualization, A.C.L. and B.D.R.; methodology, C.N.d.S. and R.M.d.S.; software, C.N.d.S.; validation, A.C.L. and B.D.R.; formal analysis, C.N.d.S.; investigation, C.N.d.S. and R.M.d.S.; resources, C.N.d.S. and R.M.d.S.; writing—original draft preparation, C.N.d.S. and R.M.d.S.; writing—review and editing, A.C.L. and B.D.R.; visualization, A.C.L. and B.D.R.; supervision, A.C.L. and B.D.R.; project administration, A.C.L. and B.D.R.; funding acquisition, A.C.L. and B.D.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

The authors acknowledge the Coordenação de Aperfeiçoamento de Pessoal deNível Superior—Brasil (CAPES—Finance Code 001), Conselho Nacional de Desenvolvimento Científico (CNPq) and Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ).

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Singh, R.; Das, R.; Sangwan, S.; Rohatgi, B.; Khanam, R.; Peera, S.K.P.G.; Das, S.; Lyngdoh, Y.A.; Langyan, S.; Shukla, A.; et al. Utilisation of agro-industrial waste for sustainable green production: A review. Environ. Sustain. 2021, 4, 619–636. [Google Scholar] [CrossRef]
  2. Turan, O.; Isci, A.; Yılmaz, M.S.; Tolun, A.; Sakiyan, O. Microwave-assisted extraction of pectin from orange peel using deep eutectic solvents. Sustain. Chem. Pharm. 2024, 37, 101352. [Google Scholar] [CrossRef]
  3. FAO. World Food and Agriculture-Statistical Yearbook; FAO: Rome, Italy, 2023; p. 384. [Google Scholar]
  4. Ortiz-Sanchez, M.; Omarini, A.B.; González-Aguirre, J.-A.; Baglioni, M.; Zygadlo, J.A.; Breccia, J.; D’Souza, R.; Lemesoff, L.; Bodeain, M.; Cardona-Alzate, C.A.; et al. Valorization routes of citrus waste in the orange value chain through the biorefinery concept: The Argentina case study. Chem. Eng. Process. Process Intensif. 2023, 189, 109407. [Google Scholar] [CrossRef]
  5. Viñas-Ospino, A.; Rita Jesus, A.; Paiva, A.; Esteve, M.J.; Frígola, A.; Blesa, J.; López-Malo, D. Comparison of green solvents for the revalorization of orange by-products: Carotenoid extraction and in vitro antioxidant activity. Food Chem. 2024, 442, 138530. [Google Scholar] [CrossRef] [PubMed]
  6. Tahir, Z.; Khan, M.I.; Ashraf, U.; Adan, I.R.D.N.; Mubarik, U. Industrial application of orange peel waste: A review. Int. J. Agric. Biosci. 2023, 12, 71–76. [Google Scholar] [CrossRef]
  7. Li, K.; Zhong, W.; Li, P.; Ren, J.; Jiang, K.; Wu, W. Recent advances in lignin antioxidant: Antioxidant mechanism, evaluation methods, influence factors and various applications. Int. J. Biol. Macromol. 2023, 251, 125992. [Google Scholar] [CrossRef] [PubMed]
  8. Liang, Z.; Veronica, V.; Huang, J.; Zhang, P.; Fang, Z. Combined effects of plant food processing by-products and high oxygen modified atmosphere packaging on the storage stability of beef patties. Food Control. 2022, 133, 108586. [Google Scholar] [CrossRef]
  9. Selahvarzi, A.; Ramezan, Y.; Sanjabi, M.R.; Mirsaeedghazi, H.; Azarikia, F.; Abedinia, A. Investigation of antimicrobial activity of orange and pomegranate peels extracts and their use as a natural preservative in a functional beverage. J. Food Meas. Charact. 2021, 15, 5683–5694. [Google Scholar] [CrossRef]
  10. Hernández, A.; Ruiz-Moyano, S.; Galván, A.I.; Merchán, A.V.; Pérez Nevado, F.; Aranda, E.; Serradilla, M.J.; Córdoba, M.d.G.; Martín, A. Anti-fungal activity of phenolic sweet orange peel extract for controlling fungi responsible for post-harvest fruit decay. Fungal Biol. 2021, 125, 143–152. [Google Scholar] [CrossRef]
  11. Tajaldini, M.; Samadi, F.; Khosravi, A.; Ghasemnejad, A.; Asadi, J. Protective and anticancer effects of orange peel extract and naringin in doxorubicin treated esophageal cancer stem cell xenograft tumor mouse model. Biomed. Pharmacother. Biomed. Pharmacother. 2020, 121, 109594. [Google Scholar] [CrossRef]
  12. Silva, M.R.; Jelley, R.E.; Carneiro, R.L.; Fedrizzi, B.; Weber, C.C.; Funari, C.S. Green solvents for the selective extraction of bioactive compounds from by-products of the coffee production chain. Innov. Food Sci. Emerg. Technol. 2023, 86, 103365. [Google Scholar] [CrossRef]
  13. Beaudor, M.; Vauchel, P.; Pradal, D.; Aljawish, A.; Phalip, V. Comparing the efficiency of extracting antioxidant polyphenols from spent coffee grounds using an innovative ultrasound-assisted extraction equipment versus conventional method. Chem. Eng. Process. Process Intensif. 2023, 188, 109358. [Google Scholar] [CrossRef]
  14. Corrado, I.; Argenziano, R.; Borselleca, E.; Moccia, F.; Panzella, L.; Pezzella, C. Cascade disassembling of spent coffee grounds into phenols, lignin and fermentable sugars en route to a green active packaging. Sep. Purif. Technol. 2024, 334, 125998. [Google Scholar] [CrossRef]
  15. Zhao, N.; Liu, Z.; Yu, T.; Yan, F. Spent coffee grounds: Present and future of environmentally friendly applications on industries-A review. Trends Food Sci. Technol. 2024, 143, 104312. [Google Scholar] [CrossRef]
  16. Solomakou, N.; Loukri, A.; Tsafrakidou, P.; Michaelidou, A.-M.; Mourtzinos, I.; Goula, A.M. Recovery of phenolic compounds from spent coffee grounds through optimized extraction processes. Sustain. Chem. Pharm. 2022, 25, 100592. [Google Scholar] [CrossRef]
  17. Hwang, H.-S.; Winkler-Moser, J.K.; Kim, Y.; Liu, S.X. Antioxidant Activity of Spent Coffee Ground Extracts Toward Soybean Oil and Fish Oil. Eur. J. Lipid Sci. Technol. 2019, 121, 1800372. [Google Scholar] [CrossRef]
  18. Bouhlal, F.; Aqil, Y.; Chamkhi, I.; Belmaghraoui, W.; Labjar, N.; Hajjaji, S.E.; Benabdellah, G.A.; Aurag, J.; Lotfi, E.M.; Mahi, M.E. GC-MS Analysis, Phenolic Compounds Quantification, Antioxidant, and Antibacterial Activities of the Hydro-alcoholic Extract of Spent Coffee Grounds. J. Biol. Act. Prod. Nat. 2020, 10, 325–337. [Google Scholar] [CrossRef]
  19. Calheiros, D.; Dias, M.I.; Calhelha, R.C.; Barros, L.; Ferreira, I.C.F.R.; Fernandes, C.; Gonçalves, T. Antifungal Activity of Spent Coffee Ground Extracts. Microorganisms 2023, 11, 242. [Google Scholar] [CrossRef]
  20. Balzano, M.; Loizzo, M.R.; Tundis, R.; Lucci, P.; Nunez, O.; Fiorini, D.; Giardinieri, A.; Frega, N.G.; Pacetti, D. Spent espresso coffee grounds as a source of anti-proliferative and antioxidant compounds. Innov. Food Sci. Emerg. Technol. 2020, 59, 102254. [Google Scholar] [CrossRef]
  21. Zhang, M.; Zhang, Z.; Gul, Z.; Tian, M.; Wang, J.; Zheng, K.; Zhao, C.; Li, C. Advances of responsive deep eutectic solvents and application in extraction and separation of bioactive compounds. J. Sep. Sci. 2023, 46, e2300098. [Google Scholar] [CrossRef]
  22. Aktaş, H.; Kurek, M.A. Deep eutectic solvents for the extraction of polyphenols from food plants. Food Chem. 2024, 444, 138629. [Google Scholar] [CrossRef] [PubMed]
  23. Gonzalez-Diaz, A.; García-Núñez, J.A. Hydrophilic deep eutectic solvents: A new generation of green and safe extraction systems for bioactive compounds obtaining from natural oil & fats—A review. Sustain. Chem. Pharm. 2023, 36, 101278. [Google Scholar] [CrossRef]
  24. Bamigbade, G.B.; Subhash, A.J.; Al-Ramadi, B.; Kamal-Eldin, A.; Gan, R.Y.; Liu, S.Q.; Ayyash, M. Gut microbiota modulation, prebiotic and bioactive characteristics of date pomace polysaccharides extracted by microwave-assisted deep eutectic solvent. Int. J. Biol. Macromol. 2024, 262, 130167. [Google Scholar] [CrossRef] [PubMed]
  25. Sportiello, L.; Favati, F.; Condelli, N.; Di Cairano, M.; Caruso, M.C.; Simonato, B.; Tolve, R.; Galgano, F. Hydrophobic deep eutectic solvents in the food sector: Focus on their use for the extraction of bioactive compounds. Food Chem. 2023, 405, 134703. [Google Scholar] [CrossRef]
  26. He, S.; Yin, F.; Wu, Y.; Wang, M.; Wang, Y.; Row, K.H.; Tang, W. Deep eutectic solvents as extraction media for food-derived biomacromolecules. TrAC Trends Anal. Chem. 2024, 171, 117521. [Google Scholar] [CrossRef]
  27. Mansour, F.R.; Bedair, A.; Hamed, M.; Magdy, G.; Ali, I.; Locatelli, M. Applications of (natural) deep eutectic solvents in liquid phase microextraction: A review. Microchem. J. 2024, 198, 110178. [Google Scholar] [CrossRef]
  28. Alchera, F.; Ginepro, M.; Giacalone, G. Microwave-assisted extraction (MAE) of bioactive compounds from blueberry by-products using a sugar-based NADES: A novelty in green chemistry. LWT 2024, 192, 115642. [Google Scholar] [CrossRef]
  29. Vo, T.P.; Phan, T.H.; Nguyen, T.H.P.; Nguyen, V.K.; Dang, T.C.T.; Nguyen, L.G.K.; Chung, T.Q.; Nguyen, H.Q.; Chau, P.T.T.; Thinh, L.D.A.; et al. Green extraction of phenolics and terpenoids from passion fruit peels using natural deep eutectic solvents. J. Food Process Eng. 2024, 47, e14503. [Google Scholar] [CrossRef]
  30. Cheng, Y.; Zhao, H.; Cui, L.; Hussain, H.; Nadolnik, L.; Zhang, Z.; Zhao, Y.; Qin, X.; Li, J.; Park, J.H.; et al. Ultrasonic-assisted extraction of flavonoids from peanut leave and stem using deep eutectic solvents and its molecular mechanism. Food Chem. 2024, 434, 137497. [Google Scholar] [CrossRef]
  31. Rashid, R.; Mohd Wani, S.; Manzoor, S.; Masoodi, F.A.; Masarat Dar, M. Green extraction of bioactive compounds from apple pomace by ultrasound assisted natural deep eutectic solvent extraction: Optimisation, comparison and bioactivity. Food Chem. 2023, 398, 133871. [Google Scholar] [CrossRef]
  32. Posta, S.D.; Gallo, V.; Ascrizzi, A.M.; Gentili, A.; De Gara, L.; Dugo, L.; Fanali, C. Development of a green ultrasound-assisted procedure for the extraction of phenolic compounds from avocado peel with deep eutectic solvents. Green Anal. Chem. 2023, 7, 100083. [Google Scholar] [CrossRef]
  33. Airouyuwa, J.O.; Mostafa, H.; Riaz, A.; Stathopoulos, C.; Maqsood, S. Natural Deep Eutectic Solvents and Microwave-Assisted Green Extraction for Efficient Recovery of Bioactive Compounds from By-Products of Date Fruit (Phoenix dactylifera L.) Processing: Modeling, Optimization, and Phenolic Characterization. Food Bioprocess Technol. 2023, 16, 824–843. [Google Scholar] [CrossRef]
  34. AOAC. Official Methods of Analysis of AOAC International; Association of Official Analytical Chemists: Washington, DC, USA, 1995. [Google Scholar]
  35. FAO. Food and Nutrition—Food Energy—Methods of Analysis and Conversion Factors; FAO: Rome, Italy, 2002; p. 87. [Google Scholar]
  36. Ribeiro, B.D.; Florindo, C.; Iff, L.C.; Coelho, M.A.Z.; Marrucho, I.M. Menthol-based Eutectic Mixtures: Hydrophobic Low Viscosity Solvents. ACS Sustain. Chem. Eng. 2015, 3, 2469–2477. [Google Scholar] [CrossRef]
  37. Santos-Martín, M.; Cubero-Cardoso, J.; González-Domínguez, R.; Cortés-Triviño, E.; Sayago, A.; Urbano, J.; Fernández-Recamales, Á. Ultrasound-assisted extraction of phenolic compounds from blueberry leaves using natural deep eutectic solvents (NADES) for the valorization of agrifood wastes. Biomass Bioenergy 2023, 175, 106882. [Google Scholar] [CrossRef]
  38. Almeida, F.D.L.; Cavalcante, R.S.; Cullen, P.J.; Frias, J.M.; Bourke, P.; Fernandes, F.A.N.; Rodrigues, S. Effects of atmospheric cold plasma and ozone on prebiotic orange juice. Innov. Food Sci. Emerg. Technol. 2015, 32, 127–135. [Google Scholar] [CrossRef]
  39. Re, R.; Pellegrini, N.; Proteggente, A.; Pannala, A.; Yang, M.; Rice-Evans, C. Antioxidant activity applying an improved ABTS radical cation decolorization assay. Free. Radic. Biol. Med. 1999, 26, 1231–1237. [Google Scholar] [CrossRef] [PubMed]
  40. Rufino, M.d.S.M.; Alves, R.E.; de Brito, E.S.; Pérez-Jiménez, J.; Saura-Calixto, F.; Mancini-Filho, J. Bioactive compounds and antioxidant capacities of 18 non-traditional tropical fruits from Brazil. Food Chem. 2010, 121, 996–1002. [Google Scholar] [CrossRef]
  41. Rufino, M.S.M.; Alves, R.E.; Brito, E.S.; Morais, S.M.; Sampaio, C.G.; Pérez-Jiménez, J.; Saura-Calixto, F.D. Comunicado Técnico 125—Metodologia científica: Determinação da atividade antioxidante total em frutas pelo método de redução do ferro (FRAP). In Embrapa Agroindústria Tropical; Embrapa: Fortaleza, Brazil, 2006; pp. 1–4. [Google Scholar]
  42. Benzie, I.F.; Strain, J.J. The ferric reducing ability of plasma (FRAP) as a measure of "antioxidant power": The FRAP assay. Anal. Biochem. 1996, 239, 70–76. [Google Scholar] [CrossRef]
  43. Hadidi, M.; Aghababaei, F.; Gonzalez-Serrano, D.J.; Goksen, G.; Trif, M.; McClements, D.J.; Moreno, A. Plant-based proteins from agro-industrial waste and by-products: Towards a more circular economy. Int. J. Biol. Macromol. 2024, 261, 129576. [Google Scholar] [CrossRef]
  44. Ribeiro, E.; Rocha, T.d.S.; Prudencio, S.H. Potential of green and roasted coffee beans and spent coffee grounds to provide bioactive peptides. Food Chem. 2021, 348, 129061. [Google Scholar] [CrossRef]
  45. Valdés, A.; Castro-Puyana, M.; Marina, M.L. Isolation of proteins from spent coffee grounds. Polyphenol removal and peptide identification in the protein hydrolysates by RP-HPLC-ESI-Q-TOF. Food Res. Int. 2020, 137, 109368. [Google Scholar] [CrossRef]
  46. Jackson-Davis, A.; White, S.; Kassama, L.S.; Coleman, S.; Shaw, A.; Mendonca, A.; Cooper, B.; Thomas-Popo, E.; Gordon, K.; London, L. A Review of Regulatory Standards and Advances in Essential Oils as Antimicrobials in Foods. J. Food Prot. 2023, 86, 100025. [Google Scholar] [CrossRef] [PubMed]
  47. Meryem, S.; Mohamed, D.; Nour-eddine, C.; Faouzi, E. Chemical composition, antibacterial and antioxidant properties of three Moroccan citrus peel essential oils. Sci. Afr. 2023, 20, e01592. [Google Scholar] [CrossRef]
  48. Loyao, A.S.; Villasica, S.L.G.; Dela Peña, P.L.L.; Go, A.W. Extraction of lipids from spent coffee grounds with non-polar renewable solvents as alternative. Ind. Crops Prod. 2018, 119, 152–161. [Google Scholar] [CrossRef]
  49. Martinez-Saez, N.; García, A.T.; Pérez, I.D.; Rebollo-Hernanz, M.; Mesías, M.; Morales, F.J.; Martín-Cabrejas, M.A.; del Castillo, M.D. Use of spent coffee grounds as food ingredient in bakery products. Food Chem. 2017, 216, 114–122. [Google Scholar] [CrossRef] [PubMed]
  50. Mussatto, S.I.; Machado, E.M.S.; Martins, S.; Teixeira, J.A.C. Production, Composition, and Application of Coffee and Its Industrial Residues. Food Bioprocess Technol. 2011, 4, 661–672. [Google Scholar] [CrossRef]
  51. Bondam, A.F.; Diolinda da Silveira, D.; Pozzada dos Santos, J.; Hoffmann, J.F. Phenolic compounds from coffee by-products: Extraction and application in the food and pharmaceutical industries. Trends Food Sci. Technol. 2022, 123, 172–186. [Google Scholar] [CrossRef]
  52. Saini, R.; Kumar, S.; Sharma, A.; Kumar, V.; Sharma, R.; Janghu, S.; Suthar, P. Deep eutectic solvents: The new generation sustainable and safe extraction systems for bioactive compounds in agri food sector: An update. J. Food Process. Preserv. 2022, 46, e16250. [Google Scholar] [CrossRef]
  53. Afrin, S.M.; Acharjee, A.; Sit, N. Convective drying of orange pomace at different temperatures and characterization of the obtained powders. J. Food Sci. Technol. 2022, 59, 1040–1052. [Google Scholar] [CrossRef]
  54. Aguilar-Raymundo, V.G.; Sánchez-Páez, R.; Gutiérrez-Salomón, A.L.; Barajas-Ramírez, J.A. Spent coffee grounds cookies: Sensory and texture characteristics, proximate composition, antioxidant activity, and total phenolic content. J. Food Process. Preserv. 2019, 43, e14223. [Google Scholar] [CrossRef]
  55. Huang, Y.-L.; Ma, Y.-S. The effect of extrusion processing on the physiochemical properties of extruded orange pomace. Food Chem. 2016, 192, 363–369. [Google Scholar] [CrossRef] [PubMed]
  56. Montemurro, M.; Casertano, M.; Vilas-Franquesa, A.; Rizzello, C.G.; Fogliano, V. Exploitation of spent coffee ground (SCG) as a source of functional compounds and growth substrate for probiotic lactic acid bacteria. LWT 2024, 198, 115974. [Google Scholar] [CrossRef]
  57. Ballesteros, L.F.; Teixeira, J.A.; Mussatto, S.I. Chemical, Functional, and Structural Properties of Spent Coffee Grounds and Coffee Silverskin. Food Bioprocess Technol. 2014, 7, 3493–3503. [Google Scholar] [CrossRef]
  58. Mendes, J.F.; Martins, J.T.; Manrich, A.; Sena Neto, A.R.; Pinheiro, A.C.M.; Mattoso, L.H.C.; Martins, M.A. Development and physical-chemical properties of pectin film reinforced with spent coffee grounds by continuous casting. Carbohydr. Polym. 2019, 210, 92–99. [Google Scholar] [CrossRef] [PubMed]
  59. Cayres, C.A.; Ascheri, J.L.R.; Couto, M.A.P.G. Evaluation of nutritional characteristics and consumers’ acceptance of gluten-free sweet biscuits made from rice-based pregelatinized composite flours containing orange pomace and soy protein isolate. SN Appl. Sci. 2021, 3, 183. [Google Scholar] [CrossRef]
  60. Barrales, F.M.; Silveira, P.; Barbosa, P.d.P.M.; Ruviaro, A.R.; Paulino, B.N.; Pastore, G.M.; Macedo, G.A.; Martinez, J. Recovery of phenolic compounds from citrus by-products using pressurized liquids—An application to orange peel. Food Bioprod. Process. 2018, 112, 9–21. [Google Scholar] [CrossRef]
  61. Omoba, O.S.; Obafaye, R.O.; Salawu, S.O.; Boligon, A.A.; Athayde, M.L. HPLC-DAD Phenolic Characterization and Antioxidant Activities of Ripe and Unripe Sweet Orange Peels. Antioxidants 2015, 4, 498–512. [Google Scholar] [CrossRef]
  62. Ozturk, B.; Winterburn, J.; Gonzalez-Miquel, M. Orange peel waste valorisation through limonene extraction using bio-based solvents. Biochem. Eng. J. 2019, 151, 107298. [Google Scholar] [CrossRef]
  63. Okur, I.; Soyler, B.; Sezer, P.; Oztop, M.H.; Alpas, H. Improving the Recovery of Phenolic Compounds from Spent Coffee Grounds (SCG) by Environmentally Friendly Extraction Techniques. Molecules 2021, 26, 613. [Google Scholar] [CrossRef]
  64. Mussatto, S.I.; Carneiro, L.M.; Silva, J.P.A.; Roberto, I.C.; Teixeira, J.A. A study on chemical constituents and sugars extraction from spent coffee grounds. Carbohydr. Polym. 2011, 83, 368–374. [Google Scholar] [CrossRef]
  65. Zeng, Y.; Zhou, W.; Yu, J.; Zhao, L.; Wang, K.; Hu, Z.; Liu, X. By-Products of Fruit and Vegetables: Antioxidant Properties of Extractable and Non-Extractable Phenolic Compounds. Antioxidants 2023, 12, 418. [Google Scholar] [CrossRef]
  66. Dorsey, B.M.; Jones, M.A. Chapter 2—Healthy components of coffee processing by-products. In Handbook of Coffee Processing By-Products; Galanakis, C.M., Ed.; Academic Press: Cambridge, MA, USA, 2017; pp. 27–62. [Google Scholar]
  67. Bener, M.; Şen, F.B.; Önem, A.N.; Bekdeşer, B.; Çelik, S.E.; Lalikoglu, M.; Aşçı, Y.S.; Capanoglu, E.; Apak, R. Microwave-assisted extraction of antioxidant compounds from by-products of Turkish hazelnut (Corylus avellana L.) using natural deep eutectic solvents: Modeling, optimization and phenolic characterization. Food Chem. 2022, 385, 132633. [Google Scholar] [CrossRef]
  68. Gómez-Urios, C.; Viñas-Ospino, A.; Puchades-Colera, P.; Blesa, J.; López-Malo, D.; Frígola, A.; Esteve, M.J. Choline chloride-based natural deep eutectic solvents for the extraction and stability of phenolic compounds, ascorbic acid, and antioxidant capacity from Citrus sinensis peel. LWT 2023, 177, 114595. [Google Scholar] [CrossRef]
  69. Saha, B.C.; Racine, F.M. Biotechnological production of mannitol and its applications. Appl. Microbiol. Biotechnol. 2011, 89, 879–891. [Google Scholar] [CrossRef] [PubMed]
  70. Lama-Muñoz, A.; Contreras, M.d.M.; Espínola, F.; Moya, M.; Romero, I.; Castro, E. Content of phenolic compounds and mannitol in olive leaves extracts from six Spanish cultivars: Extraction with the Soxhlet method and pressurized liquids. Food Chem. 2020, 320, 126626. [Google Scholar] [CrossRef]
  71. Isci, A.; Kaltschmitt, M. Recovery and recycling of deep eutectic solvents in biomass conversions: A review. Biomass Convers. Biorefinery 2022, 12, 197–226. [Google Scholar] [CrossRef]
  72. Vilková, M.; Płotka-Wasylka, J.; Andruch, V. The role of water in deep eutectic solvent-base extraction. J. Mol. Liq. 2020, 304, 112747. [Google Scholar] [CrossRef]
  73. Xu, M.; Ran, L.; Chen, N.; Fan, X.; Ren, D.; Yi, L. Polarity-dependent extraction of flavonoids from citrus peel waste using a tailor-made deep eutectic solvent. Food Chem. 2019, 297, 124970. [Google Scholar] [CrossRef]
  74. Ozturk, B.; Parkinson, C.; Gonzalez-Miquel, M. Extraction of polyphenolic antioxidants from orange peel waste using deep eutectic solvents. Sep. Purif. Technol. 2018, 206, 1–13. [Google Scholar] [CrossRef]
  75. Mokrani, A.; Madani, K. Effect of solvent, time and temperature on the extraction of phenolic compounds and antioxidant capacity of peach (Prunus persica L.) fruit. Sep. Purif. Technol. 2016, 162, 68–76. [Google Scholar] [CrossRef]
  76. Alam, M.A.; Muhammad, G.; Khan, M.N.; Mofijur, M.; Lv, Y.; Xiong, W.; Xu, J. Choline chloride-based deep eutectic solvents as green extractants for the isolation of phenolic compounds from biomass. J. Clean. Prod. 2021, 309, 127445. [Google Scholar] [CrossRef]
  77. Gómez, A.V.; Tadini, C.C.; Biswas, A.; Buttrum, M.; Kim, S.; Boddu, V.M.; Cheng, H.N. Microwave-assisted extraction of soluble sugars from banana puree with natural deep eutectic solvents (NADES). LWT-Food Sci. Technol. 2019, 107, 79–88. [Google Scholar] [CrossRef]
  78. Tzani, A.; Lymperopoulou, T.; Pitterou, I.; Karetta, I.; Belfquih, F.; Detsi, A. Development and optimization of green extraction process of spent coffee grounds using natural deep eutectic solvents. Sustain. Chem. Pharm. 2023, 34, 101144. [Google Scholar] [CrossRef]
  79. Fanali, C.; Della Posta, S.; Dugo, L.; Gentili, A.; Mondello, L.; De Gara, L. Choline-chloride and betaine-based deep eutectic solvents for green extraction of nutraceutical compounds from spent coffee ground. J. Pharm. Biomed. Anal. 2020, 189, 113421. [Google Scholar] [CrossRef]
  80. Koraqi, H.; Aydar, A.Y.; Khalid, W.; Ercisli, S.; Rustagi, S.; Ramniwas, S.; Pandiselvam, R. Ultrasound-assisted extraction with natural deep eutectic solvent for phenolic compounds recovery from Rosa damascene Mill.: Experimental design optimization using central composite design. Microchem. J. 2024, 196, 109585. [Google Scholar] [CrossRef]
  81. Zhou, P.; Wang, X.; Liu, P.; Huang, J.; Wang, C.; Pan, M.; Kuang, Z. Enhanced phenolic compounds extraction from Morus alba L. leaves by deep eutectic solvents combined with ultrasonic-assisted extraction. Ind. Crops Prod. 2018, 120, 147–154. [Google Scholar] [CrossRef]
  82. Viñas-Ospino, A.; Panić, M.; Bagović, M.; Radošević, K.; Esteve, M.J.; Radojčić Redovniković, I. Green approach to extract bioactive compounds from orange peel employing hydrophilic and hydrophobic deep eutectic solvents. Sustain. Chem. Pharm. 2023, 31, 100942. [Google Scholar] [CrossRef]
  83. Panda, D.K.; Bhargava, B.L. Molecular dynamics investigation of non-ionic deep eutectic solvents. J. Mol. Graph. Model. 2022, 113, 108152. [Google Scholar] [CrossRef]
  84. Dheyab, A.S.; Abu Bakar, M.F.; AlOmar, M.; Sabran, S.F.; Muhamad Hanafi, A.F.; Mohamad, A. Deep Eutectic Solvents (DESs) as Green Extraction Media of Beneficial Bioactive Phytochemicals. Separations 2021, 8, 176. [Google Scholar] [CrossRef]
  85. Liu, Y.; Li, J.; Fu, R.; Zhang, L.; Wang, D.; Wang, S. Enhanced extraction of natural pigments from Curcuma longa L. using natural deep eutectic solvents. Ind. Crops Prod. 2019, 140, 111620. [Google Scholar] [CrossRef]
  86. Tebbi, S.O.; Debbache-Benaida, N.; Kadri, N.; Kadi, R.; Zaidi, S. A novel strategy to improve the recovery of phenolic compounds from Pistacia lentiscus L. fruits using design-based statistical modeling for ultrasound-deep eutectic solvents extraction and the evaluation of their antioxidant potential. Sustain. Chem. Pharm. 2023, 31, 100933. [Google Scholar] [CrossRef]
  87. Lu, W.; Alam, M.A.; Pan, Y.; Wu, J.; Wang, Z.; Yuan, Z. A new approach of microalgal biomass pretreatment using deep eutectic solvents for enhanced lipid recovery for biodiesel production. Bioresour. Technol. 2016, 218, 123–128. [Google Scholar] [CrossRef] [PubMed]
  88. Barbieri, J.B.; Goltz, C.; Batistão Cavalheiro, F.; Theodoro Toci, A.; Igarashi-Mafra, L.; Mafra, M.R. Deep eutectic solvents applied in the extraction and stabilization of rosemary (Rosmarinus officinalis L.) phenolic compounds. Ind. Crops Prod. 2020, 144, 112049. [Google Scholar] [CrossRef]
  89. Kang, S.; Namgoong, H.; Son, W.S.; Kim, Y.D.; Jeong, K.M.; Jin, Y.; Won, H.-S.; Hong, J.; Jeong, J.; Lee, J. Insights into the Vastly Different Effects of Eutectic Solvents on the Stability of Phenolic Compounds. J. Phys. Chem. Lett. 2020, 11, 5268–5272. [Google Scholar] [CrossRef]
  90. Sharma, N.; Banerjee, S.; Kaushik, S.; Tomar, R.S. Comparative study of total reducing and total antioxidant capacity of Escherichia coli on different media composition obtained by response surface methodology. Res. J. Biotechnol. 2023, 18, 19–26. [Google Scholar] [CrossRef]
  91. Ortiz-Sanchez, M.; Cardona Alzate, C.A.; Solarte-Toro, J.C. Orange Peel Waste as a Source of Bioactive Compounds and Valuable Products: Insights Based on Chemical Composition and Biorefining. Biomass 2024, 4, 107–131. [Google Scholar] [CrossRef]
  92. Syed, A.A.; Reza, M.I.; Yadav, H.; Gayen, J.R. Hesperidin inhibits NOX4 mediated oxidative stress and inflammation by upregulating SIRT1 in experimental diabetic neuropathy. Exp. Gerontol. 2023, 172, 112064. [Google Scholar] [CrossRef]
  93. Apaijit, K.; Pakdeechote, P.; Maneesai, P.; Meephat, S.; Prasatthong, P.; Bunbupha, S. Hesperidin alleviates vascular dysfunction and remodelling in high-fat/high-fructose diet-fed rats by modulating oxidative stress, inflammation, AdipoR1, and eNOS expression. Tissue Cell 2022, 78, 101901. [Google Scholar] [CrossRef]
  94. Dai, Y.; Rozema, E.; Verpoorte, R.; Choi, Y.H. Application of natural deep eutectic solvents to the extraction of anthocyanins from Catharanthus roseus with high extractability and stability replacing conventional organic solvents. J. Chromatogr. A 2016, 1434, 50–56. [Google Scholar] [CrossRef]
  95. Mišan, A.; Nađpal, J.; Stupar, A.; Pojić, M.; Mandić, A.; Verpoorte, R.; Choi, Y.H. The perspectives of natural deep eutectic solvents in agri-food sector. Crit. Rev. Food Sci. Nutr. 2020, 60, 2564–2592. [Google Scholar] [CrossRef]
  96. Lee, S.Y.; Liang, Y.N.; Stuckey, D.C.; Hu, X. Single-step extraction of bioactive compounds from cruciferous vegetable (kale) waste using natural deep eutectic solvents. Sep. Purif. Technol. 2023, 317, 123677. [Google Scholar] [CrossRef]
Sustainability 16 07403 g001
Figure 1. Flowchart and mechanism of action of DES in the extraction of phenolic compounds.
Figure 1. Flowchart and mechanism of action of DES in the extraction of phenolic compounds.
Sustainability 16 07403 g001
Table 1. Physicochemical composition of orange by-products and spent coffee grounds.
Table 1. Physicochemical composition of orange by-products and spent coffee grounds.
CompositionOrange By-Products (%)Spent Coffee Grounds (%)
Moisture (dry fresh)____75.15 ± 1.85
Moisture (dry base)7.26 ± 0.064.91 ± 0.35
Proteins6.93 ± 0.0012.99 ± 0.00
Ash5.75 ± 0.011.56 ± 0.03
Lipids2.39 ± 0.106.23 ± 0.60
Carbohydrates77.67 ± 0.0974.31 ± 0.67
Caloric Value (kcal/100 g)359.89405.23
TPC (mg GAE/L)427.79 ± 6.46579.20 ± 5.75
Results are expressed as mean ± standard deviation (n = 3).
Table 2. Effect of water content on the extraction of total phenolic compounds from orange by-products and spent coffee grounds (SCG) using deep eutectic solvents (DES).
Table 2. Effect of water content on the extraction of total phenolic compounds from orange by-products and spent coffee grounds (SCG) using deep eutectic solvents (DES).
Water Content (%)Orange By-Products
(mg GAE/L)		Spent Coffee Grounds
(mg GAE/L)
CM-DESLG-DESCM-DESLG-DES
Control MeOH (80% v/v)400.20 ± 7.3 eA455.39 ± 5.43 bB611.70 ± 4.93 cA546.70 ± 6.57 bB
DES-10%786.70 ± 2.26 aA596.26 ± 1.51 aB756.70 ± 8.57 aA612.78 ± 4.52 aB
DES-20%632.70 ± 3.15 bA430.17 ± 2.61 cB643.50 ± 3.29 bA471.04 ± 6.02 cB
DES-30%603.31 ± 5.90 cA375.39 ± 6.90 dB607.19 ± 2.68 cA457.13 ± 6.02 cB
DES-40%427.22 ± 2.68 dA340.61 ± 3.01 eB429.20 ± 6.75 dA373.65 ± 1.51 dB
DES-50%279.67 ± 4.42 fB329.30 ± 6.02 eA351.30 ± 7.01 eA296.26 ± 6.57 eB
CM-DES: citric acid and mannitol, LG-DES: lactic acid and glucose. a–f Means within the same column with lowercase letters are significantly different (Tukey test, p ≤ 0.05) between different water contents for the same DES and by-product. A, B Means with uppercase letters are significantly different (t-test, p ≤ 0.05) between different solvents (CM-DES and LG-DES) for the same by-product.
Table 3. Effect of solid–liquid ratio on the extraction of total phenolic compounds from orange by-products and SCG using DES.
Table 3. Effect of solid–liquid ratio on the extraction of total phenolic compounds from orange by-products and SCG using DES.
Solid–Liquid Ratio (w/w)Orange By-Products (mg GAE/L)Spent Coffee Grounds
(mg GAE/L)
CM-DESLG-DESCM-DESLG-DES
1:5862.43 ± 6.80 cA743.42 ± 7.64 bB1363.74 ± 2.56 cA1074.25 ± 5.00 dB
1:101582.42 ± 2.42 aA1192.52 ± 1.51 aB1513.40 ± 8.57 bA1225.56 ± 4.52 cB
1:151125.12 ± 1.96 bA505.26 ± 1.44 cB1568.61 ± 8.95 aA1305.24 ± 1.45 aB
1:20670.60 ± 7.86 dA342.10 ± 1.46 dB1472.36 ± 6.34 bA1257.00 ± 4.90 bB
1:30610.00 ± 4.49 eA327.00 ± 2.50 dB1179.55 ± 7.81 dA842.10 ± 2.80 eB
1:40619.80 ± 5.22 eA185.52 ± 1.44 eB752.88 ± 3.60 eB805.50 ± 2.50 fA
1:50367.01 ± 5.15 fA187.25 ± 2.53 eB662.27 ± 5.64 fB793.94 ± 6.29 gA
CM-DES: citric acid and mannitol, LG-DES: lactic acid and glucose. a–f Means within the same column with lowercase letters are significantly different (Tukey test, p ≤ 0.05) between different solid–liquid ratios for the same DES and by-product. A, B Means with uppercase letters are significantly different (t-test, p ≤ 0.05) between different solvents (CM-DES and LG-DES) for the same by-product.
Table 4. Effect of temperature on the extraction of total phenolic compounds from orange by-products and spent coffee grounds (SCG) using deep eutectic solvents (DES).
Table 4. Effect of temperature on the extraction of total phenolic compounds from orange by-products and spent coffee grounds (SCG) using deep eutectic solvents (DES).
Temperature
(°C)		Orange By-Products
(mg GAE/L)		Spent Coffee Grounds
(mg GAE/L)
CM-DESLG-DESCM-DESLG-DES
40 °C1476.81 ± 2.63 eA1114.11 ± 2.63 eB1372.15 ± 6.65 cA1014.60 ± 5.51 eB
50 °C1540.82 ± 2.75 dA1159.42 ± 1.84 dB1395.77 ± 8.32 cA1178.11 ± 5.99 dB
60 °C1582.42 ± 2.42 cA1192.52 ± 1.51 cB1450.65 ± 2.01 bA1340.15 ± 1.66 cB
70 °C1622.00 ± 3.61 bA1356.46 ± 4.44 bB1444.12 ± 6.20 bA1389.60 ± 3.20 bB
80 °C1782.92 ± 4.50 aA1582.91 ± 3.85 aB1620.71 ± 3.72 aA1512.61 ± 8.44 aB
CM-DES: citric acid and mannitol, LG-DES: lactic acid and glucose. a–e Means within the same column with lowercase letters are significantly different (Tukey test, p ≤ 0.05) between different temperatures for the same DES and by-product. A, B Means with uppercase letters are significantly different (t-test, p ≤ 0.05) between different solvents (CM-DES and LG-DES) for the same by-product.
Table 5. Antioxidant activity of orange by-product and SCG extracts using deep eutectic solvents (DES).
Table 5. Antioxidant activity of orange by-product and SCG extracts using deep eutectic solvents (DES).
Orange By-ProductsSpent Coffee Grounds
CM-DESLG-DES 2CM-DESLG-DES
ABTS0.284 ± 0.007 aA0.133 ± 0.002 bB0.319 ± 0.002 aA0.284 ± 0.002 bB
DPPH0.233 ± 0.003 aA0.151 ± 0.001 bB0.234 ± 0.001 aA0.224 ± 0.003 bB
FRAP1.087 ± 0.004 aA0.101 ± 0.001 bB1.071 ± 0.006 aA0.367 ± 0.006 bB
CM-DES: citric acid and mannitol, LG-DES: lactic acid and glucose. a, b Means within the same column with lowercase letters are significantly different (Tukey test, p ≤ 0.05) between different methods for the same DES and by-product. A, B Means with uppercase letters are significantly different (t-test, p ≤ 0.05) between different solvents (CM-DES and LG-DES) for the same by-product. ABTS (mol equivalent Trolox/L), DPPH (mol equivalent Trolox/L), FRAP (mol ascorbic acid/L).
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Silva, C.N.d.; Silva, R.M.d.; Lemes, A.C.; Ribeiro, B.D. Recovery of Phenolic Compounds by Deep Eutectic Solvents in Orange By-Products and Spent Coffee Grounds. Sustainability 2024, 16, 7403. https://doi.org/10.3390/su16177403

AMA Style

Silva CNd, Silva RMd, Lemes AC, Ribeiro BD. Recovery of Phenolic Compounds by Deep Eutectic Solvents in Orange By-Products and Spent Coffee Grounds. Sustainability. 2024; 16(17):7403. https://doi.org/10.3390/su16177403

Chicago/Turabian Style

Silva, Cristiane Nunes da, Rhonyele Maciel da Silva, Ailton Cesar Lemes, and Bernardo Dias Ribeiro. 2024. "Recovery of Phenolic Compounds by Deep Eutectic Solvents in Orange By-Products and Spent Coffee Grounds" Sustainability 16, no. 17: 7403. https://doi.org/10.3390/su16177403

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Article metric data becomes available approximately 24 hours after publication online.
Back to TopTop