# One-step biphasic NADES extraction of phenolics and carotenoids from tomato peels with integrated life cycle assessment

Paul Sauvetes, Mias Sommer Schjønberg, Morten Birkved, Nathalie Gontard, Chahinez Aouf

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Paul Sauvetes, Mias Sommer Schjønberg, Morten Birkved, Nathalie Gontard, Chahinez Aouf. One-step biphasic NADES extraction of phenolics and carotenoids from tomato peels with integrated life cycle assessment. Separation and Purification Technology, 2026, 382 (3), pp.135865. 10.1016/j.seppur.2025.135865. hal-05493631

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# One-step biphasic NADES extraction of phenolics and carotenoids from tomato peels with integrated life cycle assessment

Paul Sauvetes<sup>a</sup>, Mias Sommer Schjønberg<sup>b</sup>, Morten Birkved<sup>b</sup>, Nathalie Gontard<sup>a</sup>, Chahinez Aouf<sup>a,*</sup>

## ARTICLE INFO

### Key words:

NADES
Biphasic system
Carotenoids
Phenolics
LCA

## ABSTRACT

A biphasic NADES extraction system composed of choline chloride:urea (ChUr) and menthol:thymol (MenThy) was developed to enable the simultaneous extraction and separation of phenolic compounds and carotenoids from tomato peels. In sequential extractions, ChUr recovered 198 µg/gDW of phenolics, primarily 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde, and MenThy enabled the extraction of 601 µg/gDW of carotenoids (lycopene and β-carotene), along with a part of flavonoids, namely quercetin (94 µg/gDW) and naringenin (50 µg/gDW). The design of a biphasic NADES system (1:1, v/v) resulted in a 40% increase in phenolic extraction, along with partial phase separation of the flavonoids: 26% of quercetin and 9% of naringenin remained in the MenThy phase. Increasing the ChUr volume to a 3:1 ratio improved partitioning, with 89% of phenolics recovered in the hydrophilic phase (ChUr). A simplified life cycle assessment (LCA) focusing on energy inputs revealed that the biphasic 1:1 system was 28% more energy efficient than the sequential extraction process, and exhibited lower CO₂-eq impacts. These findings highlight the potential of biphasic NADES systems for one-step, energy-efficient extraction and partitioning of bioactive compounds from agro-industrial residues. Further optimization of solvent polarity and composition could enhance the selectivity of this extraction process.

## 1. Introduction

In 2023, the European Union (EU) produced around 10.4 million tons of tomatoes, with Italy and Spain being the main producers [1]. Industrial tomato processing generates large quantities of by-products, known as tomato pomace, made up of peel, seed and pulp residues. It is estimated that around 15% of tomatoes processed for industrial purposes end up as waste, representing around 3 million metric tons of underutilized resources per year in Europe [2]. Whereas tomato pomace used to be dumped in landfills or partially reused for composting and animal feed [3], it is now recognized as a valuable feedstock for bioactive compounds, making it an interesting model for biorefinery approaches [4]. In particular, tomato peels are a great source of phytochemicals including phenolic compounds and carotenoids, known for their potent redox and oxygen scavenging properties [5,6].

The total phenolic compounds content (TPC) of tomato peels varies from 12.8 to 3644 mg/100 g DM, depending on tomato variety, ripening stage and extraction process [7-9]. Flavonoids such as naringenin,

quercetin, kaempferol and rutin, as well as hydroxycinnamic acids such as chlorogenic, caffeic, *p*-coumaric and ferulic acids are the predominant phenolics in commercial tomato varieties [10–13]. Notably, Stewart *et al* reported that 98% of flavonols quercetin and kaempferol in tomato are concentrated in the peel [14]. Regarding carotenoids, tomato peels are an excellent source of lycopene, β-carotene and lutein [15–17], which mainly remain in tomato residues post-processing. Depending on tomato variety, ripening stage, harvest conditions and extraction processes, lycopene content ranges from 2.62 to 629 mg/ 100 g DM, while the other carotenoids are generally between 0.23 and 2.83 mg/ 100 g DM [18].

To recover phenolics and carotenoids from plant materials, various extraction techniques have been applied, including conventional solvent extraction and non-conventional methods such as microwave-assisted, ultrasound-assisted and high hydrostatic pressure extraction [19]. Methanol and water solvents are commonly used for phenolic compounds, while ethanol, acetone, ethyl acetate or mixed polarity solvents (n-hexane-ethanol-acetone, and ethyl acetate-acetone) are employed for

<footnote><sup>a</sup> UMR 1208, INRAE Montpellier, 2 Place Pierre Viala 34060, Montpellier, France</footnote>

<footnote><sup>b</sup> SDU Life Cycle Engineering, Department of Green Technology, University of Southern Denmark, 5230 Odense, Denmark</footnote>

<footnote>* Corresponding author.
E-mail address: chahinaz.aouf@inrae.fr (C. Aouf).</footnote>
carotenoids extraction [9,10,19–22]. Recently, natural deep eutectic solvents (NADES) have emerged as a sustainable alternative due to their biodegradability, low toxicity and tunable properties. NADES are formed by combining at least one hydrogen bond acceptor (HBA) and one hydrogen bond donor (HBD), typically derived from natural metabolites like sugars, amino acids, organic acids, or choline derivatives, which become liquid at, or near room temperature [23]. By adjusting the NADES composition, extraction selectivity can be fine-tuned to meet the specific requirements of the extraction process [24]. Hydrophobic NADES such as fatty acids derivatives have been particularly effective for carotenoids extraction. For instance, among capric acid:menthol, capric acid:thymol, lauric acid:menthol, and capric acid: lauric acid, the latter in a 1 : 2 molar ratio achieved the highest carotenoids extraction from tomato at 16 mg /100g DM, in which lycopene represented 15 mg/ 100g DM [25]. From tomato pomace, lycopene was extracted at 1446 µg/g DM in menthol: lactic acid (8:1) using ultrasound-assisted extraction [26]. Under the same extraction conditions, it was extracted from tomato peels at 359 mg/g DM with menthol : thymol (1 : 1) [27]. For tomato peel phenolics, Choline chloride-based NADES have demonstrated good extraction efficiency. Vorobyova et al. [28] compared two NADES, choline chloride: 1,2-propanediol (1 : 2) and choline chloride: lactic acid (1 : 2), with 10% water. The use of lactic acid increased the total content of flavonoids (17 mg quercetin eq/g DM), and the total content of phenolic compounds (51.75 mg gallic acid eq/g DM), comparable to conventional 70% ethanol extraction. Using similar NADES, Vasyliev et al. [6] extracted 52.3 µg/g of chlorogenic acid, 14 µg/g of gallic acid and 1.47 µg/g of quercetin from tomato peels.

Despite significant progress in the individual extraction of phenolics and carotenoids from tomato residues, one-step coextraction with in-situ separation remains largely unexplored, particularly with NADES. Only three studies have evaluated biphasic DES for polarity-driven partitioning of plant metabolites. Tang et al. [29] used a hydrophilic DES (hexafluoroisopropanol: choline chloride) paired with a hydrophobic DES (menthol: tricaprylylmethylammonium) to separate polar (e.g., chlorogenic acid, anthocyanidins) from non-polar compounds (e.g., artemisinin). Cao et al. [30] developed a ternary biphasic system (two hydrophilic DES: choline chloride:levulinic acid, 1:2; choline chloride: malonic acid, 1:2; plus a hydrophobic DES: methyl trioctyl ammonium chloride: capryl alcohol: octalcy acid, 1:2:3; 35:5:40, v/v) to fractionate flavonoids, terpene trilactones, procyanidins, and polyprenyl acetates from Ginkgo biloba leaves. Vieira et al. [31] selectively separated carnosic acid/carnosol from rosmarinic acid using lactic acid: glucose (5:1) and menthol: lauric acid (2:1) on rosemary leaves. Among these studies, only Vieira et al. used a NADES system. In all cases, selectivity was attributed solely to polarity differences, with no analysis of specific NADES-solute interactions. Moreover, none examined cross-effects during sequential extraction or addressed phenolic-carotenoid pairs.

The present study investigates, for the first time, a biphasic NADES system composed of choline chloride: urea (ChUr) as the hydrophilic phase and menthol: thymol (MenThy) as the hydrophobic phase for the simultaneous extraction and selective portioning of phenolics and carotenoids from tomato peels. As a benchmark, sequential extractions using each solvent individually were performed. This process was then compared to biphasic extractions conducted at two phase ratios (1:1 and 3:1, ChUr:MenThy), assessing extraction efficiency, compound selectivity and energetic performance using a simplified life cycle (LCA) assessment approach.

## 2. Materials and methods

### 2.1. Materials

Dry tomato peels were provided by TomaPaint (Italy). Elemental analysis carried out by the biological, geological and environmental sciences lab (University of Bologna) revealed a content of 178.183 ± 75.462 µg/gDW of iron (Fe) in the peels. They were then ground using

subsequently knife mill SM300 (mill screen of 2 mm, and rotation speed of 3000 rpm); and plate mill UPZ100 (mill screen 0.3 mm, flow 1.5 Kg/h and rotation speed 18000 rpm) with a grinding yield of 98.96%. Granulometry was determined with LS 13 320 XR Beckman&Coulter laser granulometer, resulted in an average particle size D50 of around 200 µm. Peel powder with 6.22% moisture content was stored at room temperature in sealed bags in dark until use.

Lactic acid (LA, ≥85%), choline chloride (Ch, ≥98%), urea (Ur, ≥99%), DL-menthol (Men, ≥95%), thymol (Thy, 98.5%), methanol (MeOH, ≥ 99.5%), hexane (Hex, ≥95%) acetone (Ac, ≥99.5%) ethanol (Et, ≥99.5%), acetonitrile (MeCN, ≥99.9%), formic acid (HCOOH, ≥98%), methyl tert-butyl ether (MTBE, ≥99.8), hydrochloric acid (HCl, 37%), sodium hydroxide (NaOH, ≥98%), Bromothymol blue (BBT, 95%), ±naringenin (≥95%), quercetin (≥95%), 4-hydroxybenzoic acid (99%), β-carotene (95%), lycopene (≥98%), Nile Red (>97%), 2,2-Diphenyl-1-picrylhydrazyl (DPPH°, 99%) were purchased from Sigma-Aldrich. 4-hydroxybenzaldehyde (99%) was purchased from Thermo Scientific. Naringenin chalcone (≥98%) was purchased from Extra-synthese. MiliQ filtered water was used for solvent preparation and UHPLC analysis.

### 2.2. NADES preparation

The individual components were weighted to achieve the appropriate molar ratios (table 1). Then, they were mixed in a beaker covered with aluminum foil at 60 °C until a clear, homogeneous solution was obtained. All NADES were prepared and used on the same day. Prepared NADES were the following: (See Table 1).

Extractions with conventional organic solvents were used as references. Phenolic compounds were extracted with methanol (MeOH), and carotenoids were extracted with n-hexane: acetone: ethanol (Hex:Ac:Et) at 1:1:1 v:v:v.

### 2.3. Acidity measurement of NADES

Because pH measurement is unreliable in eutectic media, the method of Jablonský et al. [32] was adapted. Sodium hydroxide in 70% (v/v) ethanol was prepared at 0.15 M for ChLA and 0.06 M for MenLA. NADES (1 mL) was diluted in 10 mL of 70% ethanol and titrated using bromothymol blue. Acidity was expressed as milliequivalents of acid per kilogram of solvent (meq/kg) using Eq 1:

$$ \text{Acidity (meq/kg)} = \frac{\text{Veq(mL)} \times C_{\text{NaOH}}(\text{mol/L}) \times 1000}{m_{\text{NADES}}(\text{g})} \quad (1) $$

where CNaOH is the NaOH solution molarity, Veq, the equivalence volume, and mNADES, the mass of NADES in 1 mL.

### 2.4. Polarity evaluation of NADES

Polarity was evaluated by solubilizing Nile red in freshly prepared NADES to a concentration < 0.15 mg/mL. The absorbance spectrum was measured using an Evolution 300 UV-vis spectrophotometer (Thermo scientific), over the wavelength range of 350-650 nm with 0.2 nm step. The maximum absorption wavelength (λmax) was recorded and the normalized polarity parameter (ETNR) was calculated [33] using Eq 2:

$$ ET_{NR} = 28591/\lambda_{max} \quad (2) $$

### 2.5. Viscosity measurement of NADES

Viscosity was determined using a Lovis 2000 M microviscometer (Anton Paar) equipped with a 1.59 capillary column at 80° slope angle and 25 °C.
<table><caption>**Table 1**
List of NADES used for the extraction of phenolics and carotenoids from tomato peels.</caption><thead><tr><th>Entry</th><th>Hydrogen bond acceptor (HBA)</th><th>Hydrogen bond donor (HBD)</th><th>Ratio (mol:mol)</th><th>Water content (w/w)</th><th>HBA structure</th><th>HBD structure</th></tr></thead><tbody><tr><td>ChLA</td><td>Choline chloride</td><td>Lactic acid</td><td>1:2</td><td>10%</td><td>Image of HBA structure with N<sup>+</sup> ion and Cl<sup>-</sup> ion</td><td>Image of HBD structure with H<sup>+</sup> ion and OH<sup>-</sup> ion</td></tr><tr><td>ChUr</td><td>Choline chloride</td><td>Urea</td><td>1:2</td><td>10%</td><td>Image of HBA structure with N<sup>+</sup> ion and Cl<sup>-</sup> ion</td><td>Image of HBD structure with H<sup>+</sup> ion and H<sub>2</sub>N<sup>+</sup> ion</td></tr><tr><td>MenThy</td><td>DL-menthol</td><td>Thymol</td><td>1:1</td><td>-</td><td>Image of HBA structure with N<sup>+</sup> ion and Cl<sup>-</sup> ion</td><td>Image of HBD structure with H<sup>+</sup> ion and H<sub>2</sub>N<sup>+</sup> ion</td></tr><tr><td>MenLA</td><td>DL-menthol</td><td>Lactic acid</td><td>4:1</td><td>-</td><td>Image of HBA structure with N<sup>+</sup> ion and Cl<sup>-</sup> ion</td><td>Image of HBD structure with H<sup>+</sup> ion and H<sub>2</sub>N<sup>+</sup> ion</td></tr></tbody></table>

## 2.6. Phenolics extraction and extract treatment

Based on Vorobyova et al. [28] article and preliminary experiments, extraction of phenolics was optimized as: tomato peels (0.66 g) were mixed with 10 mL of NADES (ChLA or ChUr) in a closed 25 mL flask. The mixture was then heated at 60°C, under magnetic stirring, for 90 min. After extraction, the suspension was centrifuged at 5000 rpm during 5 min, and the supernatant solution (phenolic extract) was collected and filtered through a 0.22 µm PVDF filter.

Before UHPLC analysis, the filtered extract was mixed with acetonitrile (MeCN) at 1:3 (v/v). After 10 min, the mixture was centrifuged at 5000 rpm for 2 min. The precipitate formed was removed and the added MeCN was evaporated under vacuum at 50°C. As acetonitrile is used as one of the UHPLC mobile phases, this treatment avoids the precipitation of non-identified co-extracted compounds and the column clogging. Extraction of tomato peels with methanol under the same condition was performed as a control experiment. In this case, no extract treatment was necessary.

## 2.7. Carotenoids extraction

Based on Silva et al article [26] and preliminary experiments, extraction of carotenoids was optimized as:

tomato peels (0.66 g) were mixed with 10 mL of NADES (MenLA or MenThy) in a closed 25 mL flask. The mixture was then heated at 60°C, under magnetic stirring, for 90 min. After extraction, the suspension was centrifuged at 5000 rpm during 5 min, and the supernatant solution (phenolic extract) was collected and filtered through a 0.22 µm PVDF filter for UHPLC analysis. Extraction of tomato peels with Hex:Ac:Et (1:1:1, v/v/v) under the same condition was performed as a control experiment.

- Separation of co-extracted phenolic compounds during carotenoids extraction

MenLA and MenThy extracts were extracted with ChUr to recover coextracted phenolics. MenLA or MenThy extracts were mixed with ChUr at 1:3 (v/v), and the mixture was stirred at 60°C for 60 min. After liq-liq extraction, the two phases were centrifuged at 5000 rpm for 2 min before sampling and UHPLC analysis.

## 2.8. Sequential extractions of phenolics and carotenoids

Following the phenolic compounds extraction, the remaining plant residue was washed with 30 mL of ethanol through Büchner filter, to

remove the residual NADES. After drying at room temperature for 30 min, the subsequent carotenoids extraction was carried out under the conditions described above. The same procedure was applied when carotenoids were extracted first.

## 2.9. Extraction of phenolics and carotenoids in NADES biphasic system

A biphasic solvent system was prepared with ChUr and MenThy in two different proportions. ChUr/MenThy 1:1 (v/v), and ChUr/MenThy 3:1 (v/v). Then, the extraction of tomato peels was carried out with this system by mixing 0.66 g of peels with a total volume of 20 mL of the biphasic solvent, at 60°C for 90 min. After centrifugation at 5000 rpm for 5 min, each phase was collected and prepared for analysis, as described in the previous sections. The extraction process is represented in Fig. S1, in the supplementary Information.

## 2.10. UHPLC-MS characterization of the extracts

- UHPLC analysis

Phenolics and carotenoids identification and quantification were performed with UHPLC-DAD (ThermoFisher Ultimate 3000) equipped with a photodiode array detector (DAD), set at 280 nm for phenolics detection, and at 470 nm and 450 nm for carotenoids detection. Waters C18 column was 2.1 mm x 100 mm, HSS T3 with particle size of 1.8 µm. For phenolics elution, solvents used at 0.55 mL/min flow rate were A (99.9% H<sub>2</sub>O and 0.1% HCOOH v/v), and B (100% MeCN) with the gradient as follow: from 0 to 7 min 99.9%-60% A, from 7 to 10 min, 60%-1% A; from 12 to 13 min, 1%-99% A. For carotenoids elution, solvents used at 0.5 mL/min flow rate were A (MeOH) and B (MTBE), with the gradient as follows: from 0 to 2 min 99.9%-60% A, from 2 to 8 min 60%-1% A, from 8 to 9 min 1% A, from 9 to 10 min 1%-99.9% A.

The carotenoids present in the extract were identified by comparison with a range of commercial standards.

Quantification was carried out using calibration curves for the phenolics and carotenoid standards identified.

- Mass spectrometry identification of phenolic compounds

The identification of phenolic compounds by mass spectrometry was carried out at Laboratoire de Mesure Physique (LMP, University of Montpellier), using an Orbitrap ID-X mass spectrometer (Thermo Scientific) equipped with an ESI source. The mass spectrum was recorded in positive and negative modes, ranging from 100 to 1000 Da. The spray voltage was set to 3500 V, while the vaporization and ion transfer tube
temperatures were 400°C and 350°C, respectively. The flow rates for the Sheath gas, Aux gas, and Sweep gas were set to 60, 15, and 2 (arbitrary units), respectively. MS/MS spectra were recorded in HCD mode with a fixed collision energy of 30%. The resolution of the Orbitrap analyzer was set to 60,000 for MS mode and 30,000 for MS/MS mode.

## 2.11. Evaluation of carotenoids stability

To assess the effect of phenolic compounds on carotenoid stability over time, carotenoids extracted in the presence and absence of phenolic compounds were stored at 20°C in sealed bottles protected from light for 6 days. The evolution of lycopene and β-carotene concentration in the extracts was assessed daily by UHPLC analysis.

## 2.12. DPPH radical scavenging activity of phenolic compounds

The impact of carotenoids on the radical scavenging activity of phenolics was assessed using the DPPH° assay according to Brand-Williams et al. [34]. Preliminary tests were carried out in MenThy containing both phenolics and carotenoids. However, thymol reduced the DPPH° radical, interfering with the accurate measurement of phenolic compounds activity. Therefore, a methanolic solution, simulating the composition of the monophasic system was prepared by extracting the tomato peels in MeOH and adding 18.8 µg/mL of lycopene and 17.7 µg/mL of β-carotene solubilized in hexane. The phenolic extract solution (in presence or absence of carotenoids) was diluted 1, 2, 5, 10 and 20x in MeOH in triplicate. A 25 µL volume of each dilution was transferred to a 96 well microtest plate, followed by the addition of 175 µL of a 60 µM DPPH° solution in MeOH. Controls included a blank (25 µL MeOH+175 µL DPPH° solution) and a background (200 µL MeOH). The microplate was sealed and absorbance at 515 nm was recorded every 2 min for 3 h, using a Tecan Spark multifunctional microplate reader. For each antioxidant concentration, the percentage of residual DPPH° at the steady state was plotted as function of the mass ratio of antioxidant to DPPH°. Antiradical activity was defined as the amount of antioxidant necessary to decrease the initial concentration of DPPH° by 50%. See Eq 3

$$EC_{50} = \frac{AOX (mg/mL)}{DPPH (mg/mL)} \qquad (3)$$

## 2.13. Statistical analysis

Analysis of variance (ANOVA) was conducted using Xlstat 2022 software. Tuckey test was applied to identify pairwise differences between group means. Data were presented as mean standard deviation and differences were considered statistically significant at p < 0.05.

## 2.14. Energy consumption and global warming potential (CO₂ eq)

Life cycle assessment (LCA) methodology was applied to compare the environmental impacts of the sequential and biphasic extraction systems. Given the small-scale lab setup, the assessment was limited to the energy consumption of each process and the associated CO2 eq impacts derived from this energy use.

The energy consumption associated with the sequential and biphasic systems extraction was estimated based on the thermal energy required to heat the solvents to 60°C (heat losses and energy transfer efficiencies were ignored).

Specific heat capacities (Cp) of ChUr and MenThy were determined using differential scanning calorimetry (DSC, Q200 series, TA instruments) under nitrogen. ~50 mg of solvent was sealed in aluminum pans (triplicate analysis). The DSC temperature program consisted of an initial isothermal step at 20°C for 5min, followed by a heating ramp of 5°C/min up to 70°C, and a final isothermal step at 70°C for 5 min. Heat flow values at 60°C were used to calculate the specific heat capacity according to Eq 4:

$$C_p (J/g/K) = \frac{\text{Heat flow (W/g)}}{\text{Heating rate (K/s)}} \qquad (4)$$

The obtained Cp values were considered constant over the 20-60°C range. They were then used to estimate the energy required to heat 1 mL of each solvent system within this temperature range (ΔT = 40 K). Eq 5

$$E_{\text{NADES}} (J/mL) = C_p (J/g/K) \times \rho \left(\frac{g}{mL}\right) \times \Delta T(K) \qquad (5)$$

ρ: density of the NADES, evaluated by precise weighting of a known volume of NADES at room temperature

The total energy (Eq 6) required for each extraction process was calculated by summing the energy contributions of each solvent, according to the volumes used:

- Successive and biphasic 1:1 extraction: 10 mL ChUr + 10 mL MenThy

- Extraction/separation and biphasic 3:1: 15 mL ChUr + 5 mL MenThy.

$$E(J) = V_{\text{ChUr}}(mL) \times E_{\text{ChUr}}\left(\frac{J}{mL}\right) + V_{\text{MenThy}}(mL) \times E_{\text{MenThy}}\left(\frac{J}{mL}\right) \qquad (6)$$

Finally, the energetic efficiency of each extraction process was quantified as the specific thermal energy consumption per µg of extracted compound (phenolic and/ or carotenoids), according to Eq 7

$$\text{Specific thermal energy}(J/\mu g) = \frac{E(J)}{\text{Yield}(\mu g)} \qquad (7)$$

To perform the environmental impact assessment, the reference flow was determined to be 1 µg of product. This is to ensure that all processes will be compared equally on an environmental impact per unit output basis. Each extraction process will thus be modeled as the amount of energy used for it to produce a 1 µg output. The energy production process used in the model is “market for heat, from steam, in chemical industry, RER” from the coinvent 3.11 consequential database. [35] Steam is selected for heating as it is a typical energy carrier in full-scale chemical installations, with the market process for heat from steam chosen as it represents the average European environmental impacts. The consequential database was selected over the attributional database as this process seeks to offer decision makers guidance regarding the potential consequences of implementing a new extraction process rather than accounting for the environmental impacts of an existing process (as per the ISO 14040 standard). The impact assessment method used for calculation is the climate change method from ReCiPe 2016 Midpoint H (global warming potential, GWP100) [36], with results calculated using Brightway 2.5 [37]. The energy mixes used in both the EU-wide process and the country-specific processes are primarily fossil fuel based, with the heat and power cogeneration being entirely natural gas powered and the EU-wide industrial steam being approximately 72% gas, with the remainder being comprised of a combination of oil, coal, and wood chips. This is due to marginal energy markets – biofuels are already in high demand, and as such the markets most likely to be able to fulfill the increase in fuel demand would be the fossil fuel markets. Renewable energy such as wind, solar, and hydro power are not in consideration for providing heating as this is quite inefficient.

# 3. Results and Discussion

## 3.1. Extraction and identification of phenolics and carotenoids from tomato peels

It is worth to note that in this work, techniques such as ultrasound-assisted extraction was not employed, as the objective is not to reach the maximum extraction level of bioactive compounds, but to study the effect of extractions sequences on the content and structure of bioactive molecules.
- Extraction of phenolic compounds from tomato peels

Several studies have demonstrated improved recovery of phenolic compounds using choline chloride-based NADES, associated with organic acids as HBD[38–40]. Based on the works of Vorobyova et al. [28] and Vasyliev et al.[6], phenolic compounds from tomato peels were extracted using choline chloride: lactic acid solvent (ChLA) at 1:2 molar ratio with 10% (w/w) H₂O, at 60°C. For comparison, choline chloride: urea (ChUr) at the same molar ratio (1:2 + 10% H₂O), a solvent previously shown to efficiently extract phenolic compounds from *Pluchea indica* leaves, was also tested under similar conditions[41]. Methanol a conventional organic solvent for phenolic extraction was used as a control extraction solvent.

Phenolic compounds in the extracts were identified and quantified by HPLC-DAD-MS. Analysis results are presented in Fig. 1 (A), and Table 2. The predominant phenolic compounds in extracts from all three solvents were phenolic acid (4-hydroxybenzoic acid, 1), aldehyde (4-hydroxybenzaldehyde, 2), flavonol (quercetin, 3) and flavanone (naringenin, 4). 4-hydroxybenzoic acid was identified with m/z 137.02 (in negative ion mode), and MS2 fragmentation at m/z 93.03, corresponding to the loss of carboxylic group (CO₂). 4-Hydroxybenzaldehyde was identified with m/z 121.03, with a MS2 fragment of 92.02, characteristic COH ion for aldehydes. Quercetin was assigned to m/z 301, with MS2 fragments at m/z 193, 179, 151 and 107, consistent with fragments reported by by Hong et al.[42] in negative ion mode. In positive ion mode, naringenin derivative was identified at m/z 273 with MS2 fragments at m/z 179, 153, 147, 125 and 74. As naringenin chalcone is the predominant flavonoid in raw tomatoes, naringenin and naringenin chalcone standards were both injected in HPLC, which made it possible to attribute peak 4 to naringenin (by comparing retention times). Indeed, during tomato processing, naringenin chalcone undergoes transformation due to heat and pH, leading to an increase in naringenin concentration[43].

The phenolic composition of tomato peels is influenced by several

factors including tomato variety, ripening stage and extraction conditions. While naringenin and quercetin are well documented as major flavonoids in tomato by-products[43], only few studies have reported the presence of 4-hydroxybenzaldehyde and its oxidized form in tomato [44,45].

As shown in Table 2 and Fig. 2, the extract obtained with ChLA (244.24±10.02 µg/gDW) solvent has a higher phenolic content compared to MeOH (211.42±4.53 µg/gDW) and ChUr (198.05±5.73 µg/gDW) (p <0.05).

When phenolic compounds were categorized into flavonoids and non-flavonoids, it was observed that all three solvent systems extracted these two groups in similar proportions. Specifically, flavonoids accounted for 69%, 70%, and 73% of the total phenolics in MeOH, ChUr, and ChLA extracts, respectively, while non-flavonoids represented approximately 30% of the total phenolics on average. This indicates that the differences in polarity and pH among the three solvents did not significantly affect their selectivity for a specific group of phenolics. However, in a related study, Vasyliev et al. reported enhanced extraction of phenolic acids, including gallic, caffeic, and chlorogenic acids, when using the ChLA solvent. They attributed this improvement to the solvent's low pH, which likely facilitated the solubility and recovery of these acidic compounds[6].

- Extraction of carotenoids from tomato peels

Based on a review of the literature, two hydrophobic NADES were selected for the extraction of carotenoids from tomato peels: menthol: lactic acid (MenLA) at a 4:1 molar ratio and menthol:thymol (MenThy) at a 1:1 ratio. These were compared against a conventional organic solvent mixture (hexane:ethanol:acetone, 1:1:1) used as a reference [26,27]. Fig. 1 (B) presents the UV chromatogram of the extract at 470 nm. Using commercial standards, the two major carotenoids commonly found in tomato peels, lycopene (5) and β-carotene (6), were identified and quantified.

<figure><img src="image_4.png" /><figcaption>Fig. 1. HPLC chromatogram of phenolic compounds (A) and carotenoids (B) from tomato peels at 280 nm and 470 nm respectively.</figcaption></figure>
<table><caption>**Table 2**
Phenolic and carotenoid contents in tomato peels after NADES and organic solvents extraction.</caption><thead><tr><th rowspan="2">Solvent</th><th colspan="5">Phenolics (µg/gDW)</th><th colspan="3">Carotenoids (µg/gDW)</th></tr><tr><th>p-hydroxybenzoic acid (1)</th><th>p-hydroxybenzaldehyde (2)</th><th>quercetin (3)</th><th>naringenin (4)</th><th>Total phenolics</th><th>lycopene (5)</th><th>β-carotene (6)</th><th>Total carotenoids</th></tr></thead><tbody><tr><td>ChLA</td><td>30.27±1.90<sup>bc</sup></td><td>36.20±1.41<sup>a</sup></td><td>88.54<br/>±2.79<sup>ab</sup></td><td>89.22±3.99<sup>a</sup></td><td>244.24<br/>±10.02<sup>a</sup></td><td>-</td><td>-</td><td>-</td></tr><tr><td>ChUr</td><td>38.58±5.25<sup>ab</sup></td><td>19.12±0.55<sup>b</sup></td><td>80.47<br/>±2.20<sup>bc</sup></td><td>59.89±0.39<sup>d</sup></td><td>198.05<br/>±5.73<sup>bc</sup></td><td>-</td><td>-</td><td>-</td></tr><tr><td>MeOH</td><td>27.80±0.51<sup>bc</sup></td><td>36.36±0.92<sup>a</sup></td><td>74.18±1.42<sup>c</sup></td><td>73.08±1.58<sup>c</sup></td><td>211.42±4.53<sup>b</sup></td><td>-</td><td>-</td><td>-</td></tr><tr><td>MenLA</td><td>38.60±1.61<sup>ab</sup></td><td>36.10±0.49<sup>a</sup></td><td>60.14±2.34<sup>d</sup></td><td>80.45±0.13<sup>b</sup></td><td>215.29±2.89<sup>b</sup></td><td>201.04<br/>±25.35<sup>c</sup></td><td>203.66<br/>±3.05<sup>b</sup></td><td>404.70±25.53<sup>c</sup></td></tr><tr><td>MenThy</td><td>20.08±0.34<sup>c</sup></td><td>18.85±0.17<sup>b</sup></td><td>94.72±2.24<sup>a</sup></td><td>50.12±1.50<sup>e</sup></td><td>183.76±3.73<sup>c</sup></td><td>326.62±3.49<sup>a</sup></td><td>275.14<br/>±6.64<sup>a</sup></td><td>601.76±7.50<sup>a</sup></td></tr><tr><td>Hex:Ac:Et</td><td>44.94±8.16<sup>a</sup></td><td>37.94±1.40<sup>a</sup></td><td>33.08±5.49<sup>e</sup></td><td>62.64±1.95<sup>d</sup></td><td>178.61<br/>±10.12<sup>c</sup></td><td>282.85±0.73<sup>b</sup></td><td>266.81<br/>±5.03<sup>a</sup></td><td>549.66±5.09<sup>b</sup></td></tr></tbody></table>

<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Contents (µg/gDW) of phenolic compounds and carotenoids extracted in the different NADES and organic solvents.</figcaption></figure>

Among the tested solvents, MenThy demonstrated the highest efficiency in carotenoid extraction, yielding 601.76 ± 7.50 µg/gDW, of which lycopene accounted for 326.62 ± 3.49 µg/gDW (Table 2, Fig. 2). These results align with reported literature values for lycopene content in tomato peels [46]. Hex:Et:Ac solvent extracted about 10% less carotenoids than Men:Thy.

In addition to carotenoid extraction, both Men:LA and Men:Thy NADES facilitated the co-extraction of phenolic compounds, which will be discussed in subsequent sections.

## 3.2. Effect of sequential extractions on biomolecules content

### - Effect of phenolic compounds extraction on carotenoids

In contrast to the findings of Viñas-Ospino et al. [47], who reported the co-extraction of carotenoids (52.6 ± 0.9 mg/100 g fresh weight) while extracting phenolic compounds from orange peels using choline chloride-based NADES (ChUr, 1:1 + 30% water), no carotenoids were detected in the phenolic extracts obtained in our case.

After phenolic extraction with ChLA and ChUr, the extraction residue was washed with water and ethanol, and dried at room temperature. Then, a subsequent extraction of carotenoids, using MenThy was performed.

In the case of prior extraction with ChUr, carotenoids were recovered at 235.11±3.31µg/gDW, representing 92% of the carotenoids extracted during the one-step extraction with MenThy. In contrast, no carotenoids

were detected after phenolic extraction with ChLA (1:1), indicating complete carotenoid degradation in the presence of this acidic solvent. This is in agreement with Mortensen et al. [48] who reported the disappearance of β-carotene and the formation of other species in the presence of trifluoroacetic acid, even at low concentrations (0.05 M). This is due to the protonation of carotenoid molecules on their conjugated system, leading to isomerization from the *trans* to the less stable *cis* forms, that degrades into species with shorter conjugated system, no longer detectable at 400-500 nm. Consequently, sequential extraction of carotenoids can only be effective if the preceding phenolic extraction avoids the use of acid solvents.

### - Effect of carotenoids extraction on phenolic compounds

As previously mentioned, the carotenoid extraction using hydrophobic NADES, MenLA and MenThy, resulted in the co-extraction of phenolic compounds. MenLA extracted 215.29 ± 2.89 µg/gDW of phenolics, demonstrating lower efficiency than ChLA (244.24 ± 10.02 µg/g DW) but outperforming ChUr (198.05 ± 5.73 µg/gDW) (table 2). Men-Thy showed the lowest extractability of phenolic compounds compared with other NADES. However, it showed greater selectivity for flavonoids, particularly quercetin (94 µg/gDW). Indeed, MenThy extracted 78% of flavonoids compared to ChLA and MenLA with 73% and 65% of extracted flavonoids respectively. In addition, carotenoids were more stable over time in this solvent than in MenLA.

When studying the co-extraction of carotenoids and phenolic
compounds from plant matrices using NADES, several factors were identified as key determinants of solvent selectivity for specific groups of molecules. Among these factors, polarity, acidity and solvent viscosity are the most frequently cited. Viñas-Ospino et al.[47] observed that NADES with high polarity and low pH (e.g. proline:malic acid) are more efficient at extracting phenolic compounds than carotenoids. Similarly, Robocho et al.[49] reported that no phenolics were extracted using hydrophobic NADES composed of menthol and lauric acid. Comparing several choline chloride-based NADES, Kho et al.[50] attributed the best phenol recovery to their stability in acidic media. In addition, it has been consistently reported that lower viscosity improves solvent solubility of extracts.

In our study, ChLA (1:1 + 10% water) and MenLA (4:1) showed similar efficiency in extracting phenolic compounds. A comparison of the physicochemical characteristics of these two solvents revealed that ChLA has a higher polarity (ChLA: ET<sub>NR</sub> = 48, MenLA: ET<sub>NR</sub> = 52), and acidity (Acidity<sub>ChLA</sub> = 2262±17 meq/kg; Acidity<sub>MenLA</sub> = 736±12 meq/kg) and a lower viscosity (ChLA = 42.22 mP.s, MenLA = 53.78 mP.s) than MenLA. These attributes would typically favor ChLA for phenolic extraction. Therefore, MenLA's particular behavior in the extraction of phenolic compounds cannot be entirely attributed to its physicochemical properties. It is probably due to the specific interactions between the solvent and the extracted molecules.

NADES are known to form hydrogen bonds with various compounds, helping to disrupt plant cell tissues and enhance the extractability of target molecules [51]. Huang et al.[52] demonstrated by molecular modeling that menthol forms hydrogen bonds with quercetin, where one menthol molecule interacts with the hydroxyl group of the A ring, while another menthol molecule forms two hydrogen bonds with the hydroxyl group of the C ring and the carbonyl oxygen. This is consistent with our results, where quercetin was strongly extracted using menthol-based NADES. It is plausible that these interactions facilitate not only the extraction of quercetin, but also the recovery of other phenolic compounds through similar effect.

## 4. One step extraction/separation of phenolics and carotenoids in biphasic system

Based on the simultaneous extraction of phenolics and carotenoids using menthol-based NADES, two potential approaches can be considered depending on the targeted application. The first option is to keep the mixture of phenolics and carotenoids in the same medium, taking advantage of their combined bioactive properties. The second option is to separate the two groups of compounds to enable their individual use in specific applications.

Although NADES polarity does not drive extraction selectivity, it remains an important parameter to determine molecules affinity.

As acidic conditions favor carotenoid degradation, tomato peels were extracted with MenThy NADES, and the extract was then mixed with ChUr in a 1:3 (v/v) ratio. After 60 min at 60°C, 84% of phenolic compounds (176.82±1.10 µg/gDW) were transferred to the polar phase (ChUr), with carotenoids remaining in MenThy phase. All of 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde were transferred to ChUr phase while quercetin and naringenin were transferred at 78.8% and 84% respectively (Fig. 3). This finding prompted us to develop a one-step extraction/separation approach based on a biphasic solvent system with MenThy as the hydrophobic phase and ChUr as the hydrophilic phase. According to Florindo et al.[53] the presence of menthol (precisely its cycloalkyl group), not only enhances the hydrophobicity of DES, but also stabilizes the equilibrium of the liquid-liquid two phases. Two volume ratios were selected for the biphasic system: ChUr:MenThy (1:1, v/v) and ChUr:MenThy (3:1, v/v). In the equivolume system (1:1), carotenoid content reached 192.79±1.02 µg/gDW (75% of the maximum extracted amount, with MenThy alone), while total phenolic content was 294.45 ± 4.96 µg/gDW, representing an increase compared to single-phase extraction systems (+40% compared to MenThy alone). As reported by Tang et al.[29] phase separation in biphasic systems is not always stable, which can lead to partial miscibility between the two NADES phases. This can increase the polarity of MenThy within the biphasic system, consequently reducing its capacity to extract carotenoids. On the other hand, the presence of ChUr in the biphasic system enhanced the extraction of polar phenolic compounds such as 4-hydroxybenzoic acid, resulting in a higher total phenolic content. Notably,

<figure><img src="image_6.png" /><figcaption>Fig. 3. content (µg/gDW) of phenolic compounds and carotenoids in hydrophilic and hydrophobic phases in mono- and biphasic solvent systems.</figcaption></figure>
around 36.5% of all the phenolic compounds remained in the hydrophobic phase (MenThy), particularly quercetin (26.6% of total) and naringenin (9.9% of total). When the volume ratio of the hydrophilic to hydrophobic phase (ChUr:MenThy) was increased to a ratio of 3:1, no significant changes were observed in the total extraction yields of phenolics and carotenoids. However, 89% of phenolics were successfully recovered in the ChUr phase (only 8.3% of quercetin and 2.6% of naringenin remained in the hydrophobic phase) (Fig. 3). The increased volume of hydrophilic solvent improved the transfer of phenolics from the hydrophobic phase. It therefore appears that interactions between menthol and quercetin (and phenolic compounds in general) promote their initial solubilization in the hydrophobic phase, while the transfer to the hydrophilic phase depends primarily on its volume and polarity.

## 4.1. Stability and antioxidant activity of biomolecules in single- and biphasic solvent systems

- Influence of phenolic compounds on the stability of carotenoids over time

The stability of carotenoids expressed by their conservation over time was assessed in the presence of phenolic compounds in MenThy, and in their absence either after extraction with ChUr, or in the biphasic system (MenThy:ChUr 1:3).

Lycopene and β-carotene degradation were monitored over a 7-day period: in the dark, at room temperature and in contact with air. The amount of undegraded carotenoids was measured over time, as presented in Fig. 4.

In the absence of phenolic compounds, lycopene showed rapid degradation, with 50% of its content lost within 48 hours and only 9% remaining in the solvent after 7 days. A similar trend was observed in the biphasic system, although degradation occurred at a slightly slower rate. Under similar storage conditions (air exposure at room temperature), Asaduzzaman et al.[54] monitored lycopene degradation over a 12-day period. After 8 days, they observed a 74% loss of lycopene, which is lower than the extent of degradation observed in our study. The markedly faster degradation of lycopene in our case may be attributed to the presence of iron ions in the extract. Tomato peels were found to contain significant amounts of iron (178.18±75.5 µg/gDW), and through Fen-ton reaction, Fe³⁺ is known to promote the formation of carotenoid radical cations. These species no longer absorb in the typical

chromophoric range of carotenoids and tend to isomerize into less stable cis-forms, accelerating overall lycopene degradation.[55] Interestingly, in the presence of phenolic compounds, lycopene showed markedly improved stability, retaining its content for up to 3 days and showing only a 30% loss after 7 days. As for β-carotene, it showed greater stability under all the conditions tested, with no observable degradation in the presence of phenolic compounds. This suggests that, in addition to the stabilizing effect of NADES on carotenoids[56], interactions between phenolic compounds and carotenoids, mediated by hydrogen bonding, electrostatic interactions and Van der Waals forces, form stable complexes[57].

- Influence of carotenoids on the radical scavenging activity of phenolic compounds

The DPPH° test was carried out to assess the influence of carotenoids on the radical scavenging activity of the phenolic compounds. The antioxidant activity of phenolics (alone or in combination with carotenoids) was first evaluated in MenThy. However, this evaluation was hampered by menthol which actively reduced the DPPH radical. Since the aim was to assess the phenolic compounds activity independently of the solvent, the phenolic extract in methanol was supplemented with lycopene and β-carotene in the same proportions as in the MenThy monophasic extraction system. Comparison of EC₅₀ values between phenolic compounds alone (EC₅₀ = 0.077826 ± 0.002 gAOx/gDPPH°) and phenolics/carotenoids mixture (EC₅₀ = 0.079954 ± 0.01 gAOx/gDPPH°) revealed no significant impact of carotenoids on the radical scavenging activity of phenolic compounds in tomato peels extract.

A synergistic effect between carotenoids and phenolics in DPPH radical scavenging was not consistently observed. Hu et al.[57], who assessed the antioxidant activity of individual phenolics, carotenoids, and their combinations using the DPPH° assay, calculated interaction indexes to quantify synergy. Their results showed that certain phenolic/carotenoid pairs, such as gallic acid-lutein, exhibited a synergistic effect (interaction index: 1.134). However, this was not the case for all combinations. For instance, zeaxanthin displayed low interaction indexes with all tested phenolics: gallic acid (0.843), catechin (0.768), quercetin-3-β-glucoside (0.795), and quercetin (0.766). Similarly, the quercetin/β-carotene pair did not show a synergistic effect (interaction index: 0.909). These findings are consistent with our observations, and suggest that the DPPH° test is not the optimal method for detecting the

<figure><img src="image_7.png" /><figcaption>Fig. 4. Evolution of lycopene and β-carotene amount (%) in MenThy, over time in the presence and absence of phenolic compounds.</figcaption></figure>
synergetic antioxidant effect of those two families of molecules.

In real-life conditions, the combined effect of phenolic compounds and carotenoids has been reported. During digestion, flavonoids could enhance the protective effects to carotenoids against the oxidative processes, and promote their uptake by cells[58]. It has also been suggested that the combined effect of phenolics and carotenoids cooperates in balancing UV-induced cutaneous cellular damage, by modulating antioxidant response elements[59].

## 5. Energetic efficiency and environmental impact assessment (global warming potential) of sequential and biphasic extraction processes

A simplified Life Cycle Assessment (LCA) approach was implemented to compare the energetic performance of the sequential and biphasic extraction systems. The analysis focused exclusively on the thermal energy required to heat the solvent systems from 20 °C to 60 °C, normalized per µg of extracted target compounds. Subsequent CO₂-equivalent impacts (kgCO₂eq/µg extract) were estimated based on energy input. This evaluation represents a small-scale, laboratory-based comparison, and excludes heat losses, and energy associated with downstream operations (e.g., transfer, centrifugation, filtration).

In the biphasic extraction system, the two solvents (ChUr and Men-Thy) were considered as thermodynamically independent. Therefore, the total energy demand was calculated as the sum of the individual heating requirements of each phase.

From DSC analysis, the specific heat capacities of the solvents were determined. The measured values were Cp = 2.245 J/g/K for ChUr and Cp = 2.113 J/g/K for MenThy. Using these values, the energy required to raise the solvents temperature was calculated as 105.60 J/mL for ChUr and 78.665 J/mL for MenThy. MenThy exhibited approximately 25% lower heating energy demand compared to ChUr, likely due to weaker intermolecular forces (hydrogen bonding and van der Waals interactions) and lower polarity. In contrast, ChUr's higher heat capacity can be attributed to its ionic nature and the presence of water, which stabilizes hydrogen bonding networks and stores thermal energy through bond reorganization rather than increased molecular motion [60].

The total thermal energy input per process was calculated according to the volume of each solvent used, and normalized against the total mass of extracted phenolics and carotenoids. As shown in Fig. 5, the

biphasic 1:1 system was 28.6% more energy efficient and its CO₂ eq impact was reduced by the same amount, than the sequential extraction process. Although the absolute heating energy was comparable between systems, the higher extraction efficiency of the biphasic system contributed to a lower specific energy input and, consequently, reduced environmental burden. Increasing the ChUr:MenThy ratio to 3:1 in the biphasic system (to enhance phase separation) did not improve energy efficiency, due to the higher energy demand of ChUr. Nevertheless, this configuration still outperformed sequential extraction, with an 8.8% reduction in energy consumption and CO₂eq impacts. These results suggest that optimizing solvent polarity, as demonstrated by Tang *et al.* [29], may be more effective than altering solvent volume ratios when seeking to enhance phase selectivity.

While preliminary, this environmental assessment highlights the potential benefits of biphasic NADES-based extraction at industrial scale. The biphasic approach enables the simultaneous extraction and separation of phenolics and carotenoids in a single operation, requiring only one reactor and one centrifugation step. In contrast, sequential extraction involves two distinct reactor cycles, multiple separations, and additional cleaning operations. These add complexity, increase operational and maintenance costs, and require more processing space. The simplicity of a NADES biphasic extraction system, combined with the increased yield and one step extraction-separation gives credits to the concept for the improved recovery of tomato pomace's phenolics and carotenoids in industry.

## 6. Conclusion

This study explored the use of two natural deep eutectic solvents, choline chloride:urea (ChUr) and menthol:thymol (MenThy), for the extraction of phenolic compounds and carotenoids from tomato peels. In the sequential extraction process, polar phenolics such as 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde were primarily recovered in ChUr, whereas a significant fraction of quercetin and naringenin was extracted into MenThy. This behavior is attributed to specific hydrogen-bond interactions, particularly between menthol and quercetin.

For the first time, a biphasic NADES system was developed through the combination of these two non-miscible solvents (ChUr:MenThy, 1:1 v/v), enabling the simultaneous extraction and partial separation of the two classes of compounds. In this configuration, the extraction yields of 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde increased, while a

<figure><img src="image_8.png" /><figcaption>Fig. 5. Energy consumption and CO₂eq impact per µg of extracted molecules in sequential and biphasic extraction systems.</figcaption></figure>
portion of the flavonoids remained in the MenThy phase. To promote their transfer to the hydrophilic phase, the volume of ChUr was increased (3:1 v/v).

A simplified life cycle analysis revealed that the 1:1 biphasic system outperformed the sequential extraction in terms of energetic efficiency and showed lower CO₂-eq impacts, highlighting its potential as a cleaner and more efficient alternative.

Compared with conventional water/organic systems, a biphasic NADES provides tunable, single-step, phase-selective partitioning (via HBA/HBD choice and controlled water), better stability of labile phenolics and pigments, near-zero volatile organic compounds emissions, and compatibility with food-grade formulations. To translate these advantages to industry, selectivity must be paired with robust operation. This entails optimizing viscosity and interfacial tension, selecting hydrophobic NADES with minimal surface activity, and conditioning feeds to remove emulsifying colloids. Product recovery must be defined a priori (antisolvent precipitation, adsorption, or membrane steps) and integrated with closed-loop solvent recycle that includes dehydration, polishing, and phase-quality specifications.

## Author contribution

The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript.

## CRediT authorship contribution statement

**Paul Sauvetes:** Writing – review & editing, Methodology, Investigation. **Mias Sommer Schjønberg:** Writing – review & editing, Software, Methodology, Investigation. **Morten Birkved:** Writing – review & editing, Validation, Supervision. **Nathalie Gontard:** Writing – review & editing, Validation, Resources, Project administration, Funding acquisition. **Chahinez Aouf:** Writing – original draft, Validation, Supervision, Methodology, Conceptualization.

## Funding

The authors acknowledge financial support from the Project Agri-Loop. This project has received funding from the European Union's Horizon Europe research and innovation program under grant agreement No. 101081776. Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union. Neither the European Union nor the granting authority can be held responsible for them.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgment

Authors thanks TOMAPAINT (Italy) for providing the tomato peels. They are grateful to Annalisa Tassoni from the university of Bologna for the elemental analysis of tomato peels. They also thank the PLANET facility (https://doi.org/10.15454/1.5572338990609338E12) run by the IATE joint research unit for providing support on tomato peels grinding facilities.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.seppur.2025.135865.

## Data availability

Data will be made available on request.

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