This protocol details the utilization of a polyol-based microwave-assisted extraction method for extracting phenolic compounds and natural antioxidants, representing a practical and environmentally sustainable approach to the development of ready-to-use extracts.
The utilization of polyols as green solvents for extracting bioactive compounds from plant materials has gained attention due to their safety and inert behavior with plant bioactive chemicals. This study explores the sustainable extraction of phenolic compounds and natural antioxidants from coffee silverskin using the microwave-assisted extraction (MAE) method with polyol-based solvents: glycerin, propylene glycol (PG), butylene glycol (BG), methylpropanediol (MPD), isopentyldiol (IPD), pentylene glycol, 1,2-hexanediol, and hexylene glycol (HG). A comparative analysis was conducted on conventional and non-conventional solvent extractions, focusing on their impact on the bioactive compounds of MAE, encompassing parameters such as total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities like the 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay (DPPH), the 2,2′-azino-bis(-3-ethylbenzothiazoline-6-sulphonic acid) radical scavenging assay (ABTS), and the ferric reducing antioxidant power assay (FRAP). The highest values were observed for TPC with aqueous-1,2-hexanediol extraction (52.0 ± 3.0 mg GAE/g sample), TFC with aqueous-1,2-hexanediol extraction (20.0 ± 1.7 mg QE/g sample), DPPH with aqueous-HG extraction (13.6 ± 0.3 mg TE/g sample), ABTS with aqueous-pentylene glycol extraction (8.2 ± 0.1 mg TE/g sample), and FRAP with aqueous-HG extraction (21.1 ± 1.3 mg Fe (II) E/g sample). This research aims to advance eco-friendly extraction technology through natural plant components, promoting sustainability by minimizing hazardous chemical use while reducing time and energy consumption, with potential applications in cosmetics.
Nowadays, there is a global trend towards environmental awareness in the beauty industry, leading manufacturers to focus on green technology for extracting plant components using sustainable alternatives1. Typically, traditional solvents such as ethanol, methanol, and hexane are used to extract plant phenolic components and natural antioxidants2. Nevertheless, the presence of solvent residues within plant extracts poses a potential risk to human health, inducing skin and eye irritation3, particularly concerning their intended application in cosmetics. Consequently, it is challenging to eliminate such solvent residues from the extracts, a process that demands considerable investment in time, energy, and human resources4. Recently, superheated water, ionic liquids, deep eutectic solvents, and bio-derived solvents have emerged as promising approaches for green solvent extraction5. However, their use is still limited by product separation in aqueous-based processes. To address these challenges, the development of ready-to-use extracts emerges as a viable solution6.
Polyols are often used in cosmetic formulations as humectants because of their good polarity and ability to retain moisture from the environment7. In addition, polyols such as glycerin, propylene glycol, butylene glycol, methylpropanediol, isopentyldiol, pentylene glycol, 1,2-hexanediol, and hexylene glycol can be utilized for plant extractions. They are considered non-toxic, biodegradable, environmentally friendly, non-reactive, and safe solvents for use in plant extraction8. Additionally, polyols can withstand the heat generated during microwave-assisted extraction (MAE) due to their elevated boiling points and polarity9. These polyols are generally recognized as safe (GRAS) chemicals by the United States Food and Drug Administration (FDA). Unlike conventional solvents such as ethanol or methanol, which may require rigorous removal from the extract due to their potentially harmful effects, polyols offer the advantage of minimizing the energy, time, and costs associated with solvent removal processes10. This not only streamlines the extraction process but also enhances the overall efficiency and sustainability of the extraction method. Previous investigations have employed polyols such as propylene glycol and butylene glycol as solvents in the extraction of bioactive compounds from Camellia sinensis flowers10 and coffee pulp11, revealing significant potential for their role as sustainable alternative solvents in the plant extraction process. Thus, the continued development and optimization of a polyols-water solvent system holds the potential for significant advancements in green chemistry and sustainable industrial practices.
Generally, bioactive compounds found in plants are synthesized as secondary metabolites. These compounds can be categorized into three primary groups: terpenes and terpenoids, alkaloids, and phenolic compounds12. Various extraction methods are utilized under different conditions to isolate specific bioactive compounds from plants. Bioactive compounds from plant materials can be extracted using either conventional or non-conventional techniques. Traditional methods include maceration, reflux extraction, and hydro-distillation, while non-conventional methods consist of ultrasound-assisted extraction, enzyme-assisted extraction, microwave-assisted extraction (MAE), pulsed electric field-assisted extraction, supercritical fluid extraction, and pressurized liquid extraction13. These non-conventional methods are designed to enhance safety by utilizing safer solvents and auxiliaries, improving energy efficiency, preventing degradation of the bioactive components, and reducing environmental pollution14.
Furthermore, MAE is among the sophisticated green technologies for extracting bioactive compounds from plants. Conventional extraction procedures require significant amounts of time, energy, and high temperatures, which over time might degrade heat-sensitive bioactive compounds13. In contrast to conventional thermal extractions, MAE facilitates the extraction of bioactive compounds by generating localized heating within the sample, disrupting cell structures, and enhancing mass transfer, thereby increasing the efficiency of compound extraction. Heat is transferred from inside the plant cells by microwaves, which operate on the water molecules within the plant components13. Moreover, MAE has advanced to improve the extraction and separation of active compounds, increasing product yield, enhancing extraction efficiency, requiring fewer chemicals, and saving time and energy while preventing the destruction of bioactive compounds15.
This research focuses on the extraction of plant phenolic compounds and natural antioxidants through microwave-assisted extraction (MAE) using different types of polyols as solvents. The total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities (DPPH, ABTS, and FRAP) of polyol-based MAE extracts are determined. Additionally, polyol-based MAE is compared with MAE using conventional solvents such as water and ethanol. This research is expected to contribute to the development of environmentally sustainable extraction technology for natural components, promoting sustainability by reducing reliance on hazardous chemicals, shortening processing times, and minimizing energy consumption in raw material production for potential applications within the cosmetics industry.
The details of the reagents and the equipment used in this study are listed in the Table of Materials.
1. Experimental preparation
2. Extraction process
3. Determination of phenolic compounds
4. Determination of the antioxidant activities
5. Statistical analysis
Effect of polyols solvents and conventional solvents on total phenolic content, total flavonoid content, DPPH, FRAP, and ABTS antioxidant assays
Solvent polarity should be compatible with that of targeted active molecules to improve the extraction efficiency of bioactive substances from plants22. Experiments were conducted using various solvents (water, ethanol, glycerin, propylene glycol, butylene glycol, methylpropanediol, isopentyldiol, pentylene glycol, 1,2-hexanediol, and hexylene glycol) to assess their impact on the bioactive compounds and antioxidant activities of MAE coffee silverskin extract.
Effect of polyols solvents and conventional solvents on total phenolic content
The total phenolic content of each extraction with different solvents was analyzed. The highest phenolic content was yielded in samples with aqueous-1,2-hexanediol (52.0 ± 3.0 mg GAE/g sample), while the lowest TPC was revealed in samples with water extraction (31.4 ± 4.3 mg GAE/g sample), and these values were significantly different from those of all other conditions. The samples with aqueous-pentylene glycol yielded the second-highest TPC value, followed by samples with aqueous-butylene glycol, methylpropanediol, and other solvent systems (Figure 11A). When comparing samples with conventional solvents (water and aqueous-ethanol system) and samples with polyols-based solvents, significant differences in TPC values can be observed (p < 0.05).
Effect of polyols solvents and conventional solvents on total flavonoid content
The total flavonoid content of each extraction with different solvents was analyzed. The highest flavonoid content was yielded in samples with aqueous-1,2-hexanediol (20.0 ± 1.7 mg QE/g sample), demonstrating a significant difference from that of all other extracts. The samples with aqueous-isopentydiol revealed the lowest TFC value (8.8 ± 0.7 mg QE/g sample), which was not significantly different from aqueous-methyl propanediol, and aqueous-ethanol extracts. Moreover, the second highest TFC value was found in the sample with aqueous-pentylene glycol, followed by aqueous-hexylene glycol, aqueous-propylene glycol, aqueous-butylene glycol, and aqueous-glycerin (Figure 11B).
Effect of polyols solvents and conventional solvents on antioxidant assays
The antioxidant activities of the extracts with polyols and conventional solvents were evaluated using DPPH, ABTS, and FRAP assays. The highest value for the DPPH assay was measured in samples with aqueous-hexylene glycol (13.6 ± 0.3 mg TE/g sample) and the lowest in samples with aqueous-ethanol (4.5 ± 0.2 mg GAE/g sample), and these values were significantly different from other extracts (p < 0.05). The second highest DPPH values were observed in samples with aqueous-1,2-hexanediol, followed by aqueous-pentylene glycol, aqueous-methyl propanediol, and other solvent systems (Figure 11C).
The highest ABTS value was measured in samples with aqueous-pentylene glycol (8.2 ± 0.1 mg TE/g sample) and the lowest in samples with water (5.6 ± 0.04 mg GAE/g sample), and these values were significantly different from other extracts (p < 0.05). The second highest ABTS values were detected in aqueous-butylene glycol and aqueous-1,2-hexanediol, followed by samples with aqueous-glycerin, aqueous-methyl propanediol, and other solvent systems (Figure 11D).
The highest FRAP values were observed in samples with aqueous-hexylene glycol (21.1 ± 1.3 mg Fe (II) E/g sample and the lowest in water extraction (11.5 ± 0.2 Fe (II) E/g sample), with these values being significantly different (p < 0.05) for the remaining solvents. Moreover, the second highest FRAP values were found in samples with aqueous-pentylene glycol, followed by aqueous-butylene glycol, aqueous-glycerin, and other solvent systems (Figure 11E).
When comparing the antioxidant activities of samples with conventional solvents (water and aqueous ethanol), those containing polyols exhibited significantly higher antioxidant activities in all antioxidant assays (DPPH, ABTS, and FRAP) (p < 0.05).
Figure 1: Reaction in experimental containers and the MAE chamber. (A) Sample and solvent are added to the white inter-layer vessel of a Teflon container before extraction. (B) Each container is placed inside the microwave chamber before starting the extraction. Please click here to view a larger version of this figure.
Figure 2: Special tools for closing the reaction vessels. After adding the sample and solvent to the Teflon container, the lids are applied to the top of the container, placed in the vessel holder, and fastened tightly using the tools. Please click here to view a larger version of this figure.
Figure 3: Extraction method. (A) Extraction method, created by entering the method section. (B) The SK eT accessory is applied for the MAE process. Please click here to view a larger version of this figure.
Figure 4: Stirring rate and door lock function setting. (A) The magnetic stirrer bars inside each vessel can be activated by choosing the stirring rate. (B) The door lock function limits the temperature, allowing the chamber to be opened after extraction. Please click here to view a larger version of this figure.
Figure 5: Setting the extraction conditions. (A) Entering the table icon and setting the extraction conditions such as time, temperature, and microwave power. (B) Opening the stirrer button and choosing the blower speed. Please click here to view a larger version of this figure.
Figure 6: Setting the cooling time. Applying the cooling time to reduce the inside temperature in the MAE chamber. Please click here to view a larger version of this figure.
Figure 7: Starting the extraction process. (A) Saving the method created for extraction. (B) Clicking the play icon to start the extraction process. (C) Choosing the number of vessels to start the extraction. Please click here to view a larger version of this figure.
Figure 8: Picture of the final extract after extraction using MAE. Obtaining the supernatant after centrifuging. Please click here to view a larger version of this figure.
Figure 9: The 96 well-plates for determining the TPC, TFC, DPPH scavenging activity, ABTS scavenging activity and FRAP assay of the extracts. (A) Determining the TPC for the gallic acid standard plate from a concentration of 2.5-75 µg/mL and sample extracts. (B) Determining the TFC for the quercetin standard plate from concentrations of 2.5-50 µg/mL and TFC assay to measure sample extracts. (C) Determining the DPPH scavenging activity for the Trolox standard plate from concentrations of 0.25-12.5 µg/mL and the DPPH scavenging activity detection plate of sample extracts. (D) Determining the ABTS scavenging activity for the Trolox standard plate from concentrations of 0.25-5 µg/mL and the ABTS scavenging activity detection plate of sample extracts. (E) Determining the FRAP assay for the FeSO4 standard plate from concentrations of 0.25-10 µg/mL and the FRAP assay detection plate of sample extracts. Please click here to view a larger version of this figure.
Figure 10: The standard calibration curves for the TPC, TFC, DPPH scavenging activity, ABTS scavenging activity, and FRAP assay. (A) The standard curve for determining TPC, plotted by concentrations of the gallic acid standard and absorbance at A765. (B) The standard curve for determining TFC, plotted by concentrations of the quercetin standard and absorbance at A510. (C) The standard curve for determining DPPH scavenging activity, plotted by concentrations of the Trolox standard and % inhibition. (D) The standard curve for determining ABTS scavenging activity, plotted by concentrations of the Trolox standard and % inhibition. (E) The standard curve for measuring the FRAP assay, plotted by concentrations of the ferrous sulfate standard and absorbance at A593. Please click here to view a larger version of this figure.
Figure 11: The effect of solvent types on the TPC, TFC, DPPH scavenging activity, ABTS scavenging activity, and FRAP assay in the MAE of coffee silverskin. (A) The effect of solvent types on total phenolic content. (B) The effect of solvent types on total flavonoid content. (C) The effect of solvent types on DPPH scavenging activity. (D) The effect of solvent types on ABTS scavenging activity. (E) The effect of solvent types on the FRAP assay. Values are indicated as Mean ± SD (n = 3). Values with different superscript letters express a statistically significant difference (p < 0.05). Please click here to view a larger version of this figure.
Table 1: Gallic acid standard curve preparation. Preparing the standard concentration range of 2.5-75 µg/mL in the 96-well plate. B = blank, 1-7 = number of wells on the 96-well plate. Please click here to download this Table.
Table 2: Final concentration calculation of gallic acid standards. Preparing the standard concentration range of 2.5-75 µg/mL. Final concentrations (µg/mL) of gallic acid are calculated accordingly. Final concentration (µg/mL) = (Initial concentration (mg/ mL) × Initial volume (µL) / final volume (µL)) × (1000 µg/1 mg). Please click here to download this Table.
Table 3: Quercetin standard curve preparation. Preparing the standard concentration range of 2.5-50 µg/mL in the 96-well plate. B = blank, 1-7 = number of wells on the 96-well plate. Please click here to download this Table.
Table 4: Final concentration calculation table for quercetin standards. Preparing the standard concentration range of 2.5-50 µg/mL. Final concentrations (µg/mL) of quercetin are calculated accordingly. Final concentration (µg/mL) = (Initial concentration (mg/mL) × Initial volume (µL) / final volume (µL)) × (1000 µg/1 mg). Please click here to download this Table.
Table 5: Trolox standard curve preparation in the concentration range of 0.25-12.5 µg/mL. Preparing the standard concentration range of 0.25-12.5 µg/mL in the 96-well plate. B = blank, C = control, 1-7 = number of wells on the 96-well plate. Please click here to download this Table.
Table 6: Final concentration calculation of the Trolox standards for DPPH assay. Preparing the standard concentration range of 0.25-12.5 µg/mL including the final concentrations (µg/mL) of Trolox. Final concentration (µg/mL) = (Initial concentration (mg/mL) × Initial volume (µL) / final volume (µL)) × (1000 µg/1 mg). Please click here to download this Table.
Table 7: Trolox standard curve preparation in the concentration range of 0.25-5 µg/mL. Preparing the stock standard concentration range of 0.25-5 µg/mL in the 96-well plate. B = blank, C = control, 1-7 = number of wells on the 96-well plate. Please click here to download this Table.
Table 8: Final concentration calculation of the Trolox standards for ABTS assay. Preparing the standard concentration range of 0.25-5 µg/mL, including the final concentrations (µg/mL) of Trolox. Final concentration (µg/mL) = (Initial concentration (mg/mL) × Initial volume (µL) / final volume (µL)) × (1000 µg/1 mg). Please click here to download this Table.
Table 9: Final concentration calculation table for the FeSO4 standards. Preparing the preparation of standard concentration range of 2.5-100 µg/mL, including the final concentrations (µg/mL) of FeSO4. Final concentration (µg/mL) = (Initial concentration (mg/mL) × Initial volume (µL) / final volume (µL)) × (1000 µg/1 mg). Please click here to download this Table.
Table 10: FeSO4 standard curve preparation. Preparing the standard concentration range of 0.25-10 µg/mL in the 96-well plate. B = blank. Please click here to download this Table.
Various factors play a crucial role in the successful implementation of MAE, such as the phytochemical content of plant components, extraction duration, temperature, microwave power, solid-liquid ratio, and solvent concentration13. Plants typically exhibit varying profiles of phytochemicals; hence, the selection of natural plants rich in antioxidants and phenolic compounds is essential23. Furthermore, distinct bioactive constituents display a variety of polarities depending on the solvent used. Likewise, solvents exhibit differing polarities. Given that the polarity of solvents plays a crucial role in determining the efficacy of bioactive compound extraction from raw materials, it is imperative that the solvent's polarity aligns with that of the targeted bioactive molecules24.
In this study, various polyols were utilized to extract polyphenols and antioxidants from coffee silverskin using MAE. Polyphenols are predominantly polar, and solvents with high polarity typically enhance the yield of phenolic compounds25. Compared to samples with water and ethanol, those employing different polyols demonstrated higher efficiency in all measured responses, including TPC, TFC, and antioxidant assays such as DPPH, ABTS, and FRAP. Previous studies support the findings that aqueous-polyol mixtures can enhance the extraction yield of bioactive compounds in comparison to aqueous-ethanol mixtures9,10,11. When comparing different polyols, samples with a specific aqueous-polyol system failed to yield the highest value. However, it is interesting to note that samples with aqueous 1,2-hexanediol yielded the highest values in TPC and TFC assays. Meanwhile, those with aqueous-hexylene glycol yielded the highest values in DPPH and FRAP assays, and aqueous-pentylene glycol extract exhibited the highest values in the ABTS assay. The variation in values obtained from different assays such as TPC, TFC, DPPH, ABTS, and FRAP within aqueous-polyols systems can be attributed to several factors, including the distinctive characteristics of the polyols employed. Polyols exhibit differences in viscosity, polarity, and boiling points, directly influencing their efficacy in extracting bioactive compounds from plant materials26. One potential explanation may be attributed to the principle of "Like dissolves like", wherein the particular solvent system is the most appropriate for facilitating the mass transfer of particular bioactive compounds27. This underscores the importance of selecting a solvent with a polarity that matches that of the targeted bioactive compound.
Another possible reason might be the fact that the difference in the number of hydroxyl groups (-OH) present in the solvent significantly impacts the yield of phenolic compounds28. Among these polyols, only glycerin contains three -OH groups, while the remaining polyols in this study contain two -OH groups. Solvents with a higher number of -OH groups tend to exhibit higher viscosity compared to those with fewer29. Elevated viscosity can impede the efficient transfer of active compounds during the extraction process, thereby reducing the overall yield. Furthermore, the dielectric constant of a solvent, closely linked to its polarity, plays a crucial role in determining its ability to dissolve polar or nonpolar solutes. Solvents with higher dielectric constants are more adept at dissolving polar solutes, and those with lower better suited to nonpolar solutes30. Among polyols, glycerin exhibits a comparatively high dielectric constant of 41.14, while hexylene glycol, pentylene glycol, and 1,2-hexanediol demonstrate lower dielectric constants of 25.86, 17.31, and 15.45, respectively31,32. The findings of this study suggest that the bioactive compounds within the sample may encompass low-polar constituents.
Extraction efficiency can be enhanced by optimizing the selection and composition of solvents, and further experimentation may be required to identify the most suitable solvent system. Although the investigation exhibits potential, it is limited by its sole focus on microwave-assisted extraction with polyols and its restricted evaluation of other variables, including extraction duration, temperature, solvent concentration, solid-liquid ratio, and extraction power. In addition, a mechanistic study is necessary to understand how polyols function due to their varied dielectric constants, directly impacting their solubility of polar or nonpolar solutes. Differences in dielectric constants among polyols highlight the importance of investigating their specific mechanisms in extracting bioactive compounds. Such research would offer valuable insights into solvent-solute interactions, aiding the optimization and selection of solvent systems for efficient extraction processes.
Regarding the MAE process, there are some limitations. While MAE can provide rapid heating, precise temperature control may be challenging, potentially leading to overheating and the degradation of thermally sensitive compounds33. However, the microwave power setting for gradient and extraction temperature can be set to the same microwave power to avoid temperature frustration during extraction. Additionally, MAE has limitations over heat-sensitive plant components. However, advanced Ethos X MAE technology can minimize the risk of deterioration by supporting effective heating at a shorter duration using dielectric heating34. Each vessel of the MAE chamber has its own limited maximum solid and liquid capacity. The solid-liquid ratio over this limitation can also greatly influence the concentration of the extracts11. The dissolution between solvent and solute can be promoted using stirrer bars, potentially leading to effective extraction and higher yield35. Furthermore, the extracted phenolic and flavonoid compounds within the extracts can be verified through additional analysis, such as Liquid Chromatography Triple Quadrupole Mass Spectrometry (LC-QQQ) and Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry (LC-QTOF), to establish the presence of specific bioactive compounds and their respective quantities36.
The extraction of polyphenols and antioxidants from coffee silverskin using aqueous polyols through MAE demonstrated higher efficiency in comparison to water and aqueous-ethanol extracts. Based on the outcomes derived from the polyols-based MAE of CS extracts, it has been observed that the employment of the aqueous-hexylene glycol, aqueous-1,2-hexanediol, and aqueous-pentylene glycol systems resulted in significantly higher extraction yields of bioactive compounds and antioxidant capacities. Moreover, these findings underscore the potential of utilizing such extracted compounds for subsequent investigative analyses. The utilization of polyols as green solvents for bioactive compound extraction from plant materials through MAE promises environmental benefits and enhanced bioactive compound yield, offering a sustainable approach with the potential for use in cosmetic applications.
The authors have nothing to disclose.
This study was funded by Mae Fah Luang University. The authors would like to acknowledge the Tea and Coffee Institute of Mae Fah Luang University for facilitating the connection between the researchers and local farmers concerning the acquisition of coffee silverskin samples.
1,2-Hexanediol | Chanjao Longevity Co., Ltd. | ||
2,2 -Azino-bis 3 ethylbenzothiazoline-6-sulfonic acid diammonium salt (ABTS) | Sigma | A1888 | |
2,2-Diphenyl-1-picrylhydrazyl (DPPH) | Sigma | D9132 | |
2,4,6-Tri(2-pyridyl)-s-triazine (TPTZ) | Sigma | 93285 | |
2-Digital balance | Ohaus | Pioneer | |
4-Digital balance | Denver | SI-234 | |
6-hydroxy-2,5,7,8 tetramethylchroman -2-carboxylic acid (Trolox) | Sigma | 238813 | |
96-well plate | SPL Life Science | ||
Absolute ethanol | RCI Labscan | 64175 | |
Acetic acid | RCI Labscan | 64197 | |
Aluminum chloride | Loba Chemie | 898 | |
Automatic pipette | Labnet | Biopett | |
Butylene glycol | Chanjao Longevity Co., Ltd. | ||
Ethos X advanced microwave extraction | Milestone Srl, Sorisole, Italy | ||
Ferrous sulfate | Ajex Finechem | 3850 | |
Folin-Ciocalteu's reagent | Loba Chemie | 3870 | |
Freezer SF | Sanyo | C697(GYN) | |
Gallic acid | Sigma | 398225 | |
Grinder | Ou Hardware Products Co.,Ltd | ||
Hexylene glycol | Chanjao Longevity Co., Ltd. | ||
Hydrochloric acid (37%) | RCI Labscan | AR1107 | |
Iron (III) chloride | Loba Chemie | 3820 | |
Isopentyldiol | Chanjao Longevity Co., Ltd. | ||
Methanol | RCI Labscan | 67561 | |
Methylpropanediol | Chanjao Longevity Co., Ltd. | ||
Pentylene glycol | Chanjao Longevity Co., Ltd. | ||
Potassium persulfate | Loba Chemie | 5420 | |
Propylene glycol | Chanjao Longevity Co., Ltd. | ||
Quercetin | Sigma | Q4951 | |
Refrigerated centrifuge | Hettich | ||
Sodium acetate | Loba Chemie | 5758 | |
Sodium carbonate | Loba Chemie | 5810 | |
Sodium hydroxide | RCI Labscan | AR1325 | |
Sodium nitrite | Loba Chemie | 5954 | |
SPECTROstar Nano microplate reader | BMG- LABTECH | ||
SPSS software | IBM SPSS Statistics 20 | ||
Tray dryer | France Etuves | XUE343 |
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