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Download PDF Article Open access Published: 08 May 2025 Optimization of polyphenols extraction by deep eutectic solvent from broccoli stem and characterization of their composition and

antioxidative effects Bingqing Wang1, Peiyun Chen1, Huien Zhang1, Yanlei Chen1 & …Liqing Chen1 Show authors Scientific Reports volume 15, Article number: 16066 (2025) Cite this article

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Broccoli stem is known to possess abundant polyphenols. To efficiently extract polyphenols from broccoli stems, we herein describe an updated deep eutectic solvent extraction (DESE) method.

Response surface modeling was utilized for optimization of the DESE method, achieving the best yield of 5.10 ± 0.04 mg polyphenols/g broccoli stem powder under the following conditions:

solvent, choline chloride-urea (molar ratio 1:3); extraction temperature, 80 °C; extraction duration, 55 min; water content, 60%; and liquid-solid ratio, 41:1 mL/g. Ultra Performance Liquid

Chromatography-ElectrosprayIonization-Quadrupole Time-of-Flight/Mass Spectrometry (UPLC-ESI-QTOF/MS) was then employed for characterization of the main -composition, which revealed sinapinic

acid (5.32%), trans-cinnamic acid (88.8%), quercetin (3.06%) and isochlorogenic acid (2.88%) as the dominant polyphenol compounds, and the extraction mechanism of the high efficiency of DES

was dicussed. Moreover, the extracts from (ChCl-urea) DES exhibited remarkable antioxidant activity in vitro antioxidant test. These findings provide a viable and practical approach for

broccoli culm polyphenol extraction and analysis, providing a methodological and knowledge basis for recycling broccoli wastes in an eco-friendly fashion.

others Optimization of microwave-assisted extraction of antioxidant compounds from spring onion leaves using Box–Behnken design Article Open access 10 September 2023 Optimization of

combined subcritical water and CO2 extraction for enhanced phenolics and antioxidant activity from coffee byproducts Article Open access 15 March 2025 Boosting antioxidative polyphenols

extraction efficiency via nano sized pomegranate peel particles Article Open access 07 May 2025 Introduction

Broccoli (Brassica oleracea var. italica) is a globally-distributed annual plant of the Bassicaceae family related with cauliflower, cabbage, kale and brussels sprouts1. Broccoli enjoys

popularity among consumers and is of great health significance because it contains many nutrients (protein, fibre, minerals, vitamins) and phytochemicals (glucosinolates, phenolic

compounds)2,3,4,5,6. However, the edible part of broccoli, mainly the florets, accounts for less than half of the whole broccoli, while stems and leaves totally account for over 95% of the

weight of the whole plant7,8,9.

Numerous studies have showed that broccoli stem and leaf waste is rich in nutrients and bioactive components with potential preventative and therapeutic effects against human disorders10,11.

Polyphenols are a group of bioactive compounds that are primarily synthesised by plants12. They possess multiple phenol structural units and are good antioxidants and free radical

scavengers. Polyphenols removes free radicals from the body, prevents and treats circulatory system diseases, and prevents the deterioration of physiological functions13,14, which can

protect proteins, lipids, and carbohydrates from oxidative damage, thereby decreasing the risk of various chronic illnesses15. Consequently, polyphenols are considered a valuable source of

nutraceuticals in both food and organism lines.

Separation and extraction is an important part in the research of plant polyphenols. Solvents such as methanol and its aqueous solutions, ethyl acetate andacetone have gained widespread

application for plant polyphenol isolation16,17,18. However, these conventional solvents are not eco-friendly or safe, They also don’t extract products of different polarities well and can

not maintain their bioactivity19,20.

Deep Eutectic Solvents (DESs) are a type of green and efficient extraction solvent developed in recent years. DESs are generally custom-designed that possess the capacity for

self-association frequently by means of hydrogen bond. interactions21. DESs are usually composed of biocompatible, eco-friendly, inexpensive and recoverable substances with ideal ionic

liquid attributes, including thermal and chemical inertia and superb solubility22,23. The utilization of DESs as solvents in polyphenol isolation from natural resources has already been

described24. For instance, Wang et al.25 employed DESs for extracting Ficus carica leave polyphenols; Wei et al.26 utilized maltose and choline chloride as a pair of DES to extract compounds

of different polarities, which was better than using conventional solvents. Ruan et al.27 extracted the main polyphenols in Tieguanyin oolong tea using a DES made from lactic acid and

betaine. DESs extraction agent provides a eco-friendly new extraction method with high efficiency. However, research on broccoli stem polyphenol isolation with DESs remains scarce.

Therefore, we herein developed a highly efficient and nonpolluting DES (ChCl-urea) extraction strategy for polyphenols within the discarded stems of broccoli. Response surface modeling (RSM)

with Box-Behnken design (BBD) was utilized for determining the optimal methodological parameters. The main polyphenol constituents were identified by UPLC-ESI-Q-TOF/MS. Additionally, the

extracted polyphenols were also tested in vitro for their capabilities of scavenging DPPH and ABTS free radicals, ORAC total antioxidant capacity and ferric reducing antioxidant power (FRAP)

to appraise their application prospects in food industry and clinical settings.

Fresh broccoli samples were acquired in a local supermarket (Ningbo, China). Standard gallic acid was obtained from Yuanye Biotechnology Co., Ltd. Chemical Corporation (Shanghai, China).

Reagents containing Folin-Ciocalteu reagent, citric acid, glucose, sucrose, urea, choline chloride, sodium carbonate, 2,2 -Azinobis-(3- ethylbenzthiazoline-6-sulphonate) (ABTS),

1,1-diphenyl-2-picrylhydrazyl (DPPH), ORAC and FRAP assay kits were procured from Sinopharm Group Chemical Reagent Co. Ltd. (Shanghai, China). All reagents utilized in this research were of

analytical-grade purity.

DESs were prepared according to literature methods28,29 Four types of DESs were generated by a heating protocol, which started from stir-mixing two DES components in a glass flask with round

bottom on a magnetic stirrer with constant temperature (80 °C). After 40–60 min, this step was stopped once the formation of a homogeneous mixture was observed. After incubation 30 min at

ambient temperature, a transparent and colourless concentrated solution was obtained. The composition, molar ratios and codes of DESs utilized are summarized in Table 1.

constituents and their molar ratios in analyzed DESs.Full size tableExtraction of polyphenols

The stems of fresh broccoli were rinsed with tap water, processed into 1-cm pieces, and subjected to oven-drying at 60 °C (DHG-9053 A, Electric Heating Constant Temperature Blast Drying

Oven, Yilin Scientific Instrument Co., Ltd, Shanghai, China) until the weight became constant. The samples were then mashed into powder using a food processor (Joyoung Corporation., Ltd,

Zhejiang China), which was passed through a 60-mesh sieve.

Polyphenols within the samples were extracted according to the previously described method30,31 For all experiments, a quantity of 0.25 g of broccoli stem powder was placed with a certain

amount of DES solution, water or 70% ethanol, mixed by vortex shaking evenly, and water-bathed a certain period of time (5 min shaken by vortexing once) with the temperature maintained

unchanged (QL861 Vortex Shaker, Qilin Bell Instrument Manufacturing Co., Ltd.Haimen, China). After equilibrating the mixture transiently to room temperature, it was subjected to a 20-min

centrifugation (LC-180 Centrifuge, Keda Innovation Incorporation, Ltd. China) at 5,000 rpm for supernatant collection.

Total polyphenol contents were determined based on the Folin-Ciocalteu method31, with gallic acid being utilized for standard curve establishment. Gallic acid standard working solutions with

concentrations of 0–50 µg/mL (with 10 µg/mL intervals) were prepared respectively, distilled water (for blank control) into a 25 mL colorimetric tube, add 5.0 mL of Folin-Ciocalteu reagent,

shake well. Within 3 min ~ 8 min of the reaction, add 4.0 mL of 7.5% Na2CO3 solution, make up the volume with water and shake well. After a 1-h reaction in darkness at ambient temperature,

the 765-nm absorbance (A) was determined with a spectrophotometer and the A value was determined for 3 times in parallel. The standard curve for gallic acid is obtained as y = 10.8771x + 

0.0032, R2 = 0.9991. The outcomes are presented in the form of milligram of gallic acid equivalent (GAE) per gram of dry matter (mg GAE/g DM).

m1\times{\frac{V_{1}}{V}}\times{m}\times1000$$

where m1is Content of gallic acid found in standard equation(mg/mL); V1 is Total volume of extraction(mL); V denotes the volume of sample utilized for measurement (mL); m represents sample

amount (g).

We primarily analyzed the effects of different solvents on polyphenol yield, the extraction solvent was selected, Following a single-factorial design, Extraction Solvents we explored the

effects of independent variables, namely liquid-solid ratio (10–70 (mL/g), with intervals of 10), extraction time (10–90 min, with 20-min intervals), extraction temperature (40–90 °C, with

intervals of 10 °C), and water content (10–100% (w/w), with intervals of 10%) on polyphenol yield as the dependent variable, for DES2 with molecular ratios of 1:2, 1:1, 2:1, 3:1 and 4:1.

Based on the results of the univariate experiments, the extraction parameters were then optimized by RSM based on Design-Expert 10.0.7. Table 2 displays the designed levels and coding for

RSM factors, with data representing values from three replicates of one assay. The BBD analysis data were subjected to regression analysis. The accuracy of RSM was verified by repeating the

extraction procedures thrice under the optimized conditions. The polyphenols isolated from broccoli stem utilizing the optimized parameters were further characterized for their structures

and biological effects.

Chromatographic separation and detection in the samples were analysed using a Waters synpat G2 (UPLC-ESI-QTOF/MS) system. Samples were chromatographically separated utilizing a reverse-phase

ACQUITY UPLC C18 column (100 mm × 2.1 mm × 1.7 μm), during which a 2-µL injection volume and a 0.2-mL/min flow rate were adopted. The mobile phase was prepared by mixing water (A) with

acetonitrile (B), the proportions of which were adjusted in accordance with the following scheme during the gradient elution procedure: 5% B, 0–1.0 min; 5–100% B, 1.0–12.0 min; 100% B,

12.0–13.0 min; 100 − 50% B, 13.0–15.0 min. The negative-ion ESI mode was adopted for sample analysis, spanning a 50–1200 m/z range. The desolvation gas temperature and flow of 350 °C and 900

L/h were applied. Cone hole and capillary voltages of 49.0 and 3.0 kV were utilized for mass spectra acquisition. MassLynx v.4.1 was operated for instrument control and acquisition of

data.

Antioxidative abilities of extraction of broccoli stem sample were compared with water and 70% ethanol solution. The DPPH-scavenging ability was appraised in accordance with a

previously-described procedure32. First, a DPPH solution (50 µg/mL) was mixed thoroughly with 1 mL broccoli stem extract in a closely-capped tube. The mixture was subjected to a 0.5-h

incubation at ambient temperature, after which the 517-nm optical densities (OD517) of the samples were tested with anhydrous ethanol as the blank control. Three replicates were tested

concurrently for each sample. The following equation was employed for calculating the DPPH scavenging rate:

\right)=\bigg[1-\frac{(A_{2}-A_{1})}{A_{0}}\bigg] \times {\text{ 1}}00\%$$

In which A2, A1 and A0 respectively denote OD517 values of 1 mL extract + 3 mL DPPH solution, 1 mL extract + 3 mL ethanol and 1 mL DES solvent + 3 mL DPPH solution

mixtures.

The ABTS-scavenging ability evaluation protocol was modified based on a previously-described procedure33. Briefly, a 4.5-mM K2S2O8 solution was mixed thoroughly with a 7.4-mM ABTS solution

to produce an ABTS reserve solution, which was then subjected to a 12–16-h incubation at 25 °C till the solution colour turned dark blue-green. The ABTS reserve solution was then diluted

into a concentration of 2 mM with 95% ethanol, and 200 µL of this diluted solution was mixed with an equal volume of antioxidant solutions with various concentrations. A control group was

included in the assays, for which the antioxidants were not added. The following equation was employed for calculating the ABTS scavenging rate:

\% \right)=\bigg[1-\frac{(A_{2}-A_{1})}{A_{0}}\bigg] \times {\text{ 1}}00\%$$

In which A2 represents the absorbance at 734 nm of 200µL of ABTS solution after adding 200µLof extract; A1 is the absorbance at 734 nm of 200µL of extract and 200µL of 95% ethanol; A0 is the

absorbance at 734 nm of 200µL of ABTS solution and 200µL of solvent(DES).

Total antioxidant capacity was appraised by an FRAP-based Total Antioxidant Capacity Colorimetric Assay Kit (Yuan Yea, Shanghai). The FRAP working solution with deionised water was prepared

from the kit stock solution. 30 uL of ferrous ion standard solution with different gradient concentrations were added to 264 uL of FRAP solution respectively. A blank control group with

samples replaced by deionised water was also included in the assays. The reaction mixtures were sequentially subjected to vortexing and a 30 min incubation at 37 °C under darkness. Finally,

a pectrophotometer was employed for measuring 593 nm optical absorbance.

The Oxygen Radical Antioxidant Capacity(ORAC) of the extract was evaluated using the test kit (Yuan ye, Shanghai). The antioxidant effects of samples were determined based on their abilities

for scavenging oxygen radicals, which otherwise would reduce the fluorescence intensity of fluorescein probes. Trolox solutions with concentrations of 0–40 µM were utilized in these assays

to establish an antioxidant standard curve, based on which the antioxidant capabilities of test samples were quantitatively analyzed. The linear regression equation for the antioxidant

standard curve was y = 3.943x-2.003, with a high degree of fit (r2 = 0.979).

COSMOthermX based on the COSMO-RS theory was used to calculate the thermodynamic properties of the systems containing deep eutectic solvents. The structures of the involved compounds were

optimized using TmoleX18 to obtain the σ-profile and σ-potential at BP/def-TZVP basis set.

All determinations were performed ≥ 3 times. All results are presented as mean ± standard deviation (SD) Statistically significant variations between groups were identified with analysis of

variance (ANOVA) followed by Fisher’s least significant difference (LSD) method utilizing SPSS 19. P values less than 0.05 were deemed to signify differences with statistical significance.

Error bars in artworks correspond to the 95% confidence level.

polyphenol yield

Extraction solvents are a crucial factor influencing the yield of final natural products. Considering that the extraction solvents’ permeability within broccoli stem specimens may be largely

affected by their physicochemical characteristics34, Table 1 summarizes the constituents and their molar ratios in analyzed DESs. We also compared the polyphenol yields of using hot water

and 70% ethanol as the solvents with those of DES-based methods. As shown in Fig. 1A, the yield of polyphenols differed notably among the tested solvents, with that of the DES-1 group being

markedly lower than those of others (p < 0.05). Additionally, the DES-3 and DES-4 groups exhibited comparable polyphenol extraction efficiencies (p > 0.05). DES2 exhibited a significantly

higher extraction efficiency than others, reaching 5.051 ± 0.04 mg.g−1. DW.This could be attributed to the low viscosity, relatively large diffusion coefficient, good flowability, better

permeability to the cell wall and the presence of a certain viscosity, which promoted the suspension and dispersion of broccoli stem powder within the solvent and increased the

solute-solvent contact surface, thereby facilitating polyphenol extraction. Therefore, we further optimized the extraction protocol based on the DES system consisting of choline chloride and

urea (DES-2).

As shown in Fig. 1B, adjusting the compostion ratio of DES-2 resulted in notable alterations in polyphenol extraction efficiency. Specifically, enhancing the proportion of urea within DES-2

elevated polyphenol yield, with the highest yield obtained at the urea/choline ratio of 3:1. It may be due to urea improving DES-2’s polarity which facilitates the dissolution of polyphenols

from broccoli. As the urea/ChCl ratio further increased, made the viscosity of DESs larger, resulting in poor fluidity, which made the subsequent extraction process difficult35. Therefore,

further analyses were carried out based on the urea/ChCl ratio of 2:1.

We next explored if DES water content could affect polyphenol yield. Indeed, distint polyphenol yields were noted under varied DES water contents (Fig. 1C). Specifically, enhancing the water

content of DES-2 from 10 to 60% boosted the yield from 13.82 ± 0.05% to 50.83 ± 0.04%. When the water content exceeded 70%, however, the yield was markedly reduced by subsequent increases

in water content. This might be attributed to the alterations in the viscosity, solubility, and relative polarity of the DES extraction solvent, which are associated with the presence of

water36. Additionally, the excessive addition of water can result in the destruction of DES37.

Considering these findings, further investigations were performed based on a DES-2 water content of 60%.

Our findings revealed that extraction time exerted differential impacts on polyphenol yield before and after an inflection point that appeared at the 50 th minute during a 90-min

experimental procedure (Fig. 1D). Before the inflection point, the yield of polyphenols rised from 4.16 to 4.87 mg/g with extraction time; after the inflection point, however, polyphenol

yield declined from 4.87 to 3.03 mg/g (Fig. 1D). One feasible explanation is that the prolongation of the extraction time may destruct the cell membrane, enhancing cell permeability and

facilitating polyphenol extraction; whereas a long-term extraction at high temperature may lead to the decomposition of the extracted polyphenolic compounds. Therefore, subsequent assays

were performed based on an extraction time of 50 min.

The effects of extraction temperature ranging from 40–90℃ on polyphenol yield were explored. As exhibited by Fig. 1E, extraction temperature affected polyphenol yield differentially before

and after an inflection point that was observed at an extraction temperature of 80℃. Before the inflection point, enhancing extraction temperature elevated polyphenol yield; whereas after

the inflection point, further elevating extraction temperature resulted in a significanly diminished polyphenol yield (p< 0.05). One possible explanation for this observation is that the

initial increase in extraction temperature simultaneously facilitated DES-2 dispersion and diminished its viscosity, while also expedited polyphenol transportation38, thereby boosting

polyphenol dissolution and augmenting its extraction yield. An extraction temperature exceeding 80℃, however, will damage the structure of the polyphenols. Therefore, the following

investigations were carried out with 80℃ as the optimized extraction temperature.

The impacts of liquid-solid ratio ranging from 10:1 to 70:1 (mL/g) on polyphenol yield were evaluated. According to our experimental data displayed in Fig. 1F, liquid-solid ratio was a

crucial determining factor for polyphenol extraction efficiency. The highest yield of 5.12 mg/g was observed at the liquid-solid ratio of 40:1, before which enhancing the liquid-solid ratio

heightened polyphenol yield. After this ratio, however, polyphenol yield seemed to exhibit a negative correlation with the liquid-solid ratio. It is reasonable to speculate that the initial

increases in DES-2 amount elevated solute-solvent contact surface and the concentration gradient, which is conducive to the dissolution of polyphenols, However, when the material-liquid

ratio exceeds the extraction equilibrium state or even saturates, it will increase impurity dissolution, compete for and hinder the dissolution of polyphenols. And the excessively high

material-liquid ratio increases the experimental cost37. Therefore, we selected 40:1 (mL/g) as the optimized liquid-solid ratio for this research.

Effects of different extraction parameters, namely (A) DES system, (B) composition ratio, (C) water content, (D) extraction time, (E) extraction temperature and (F) liquid-solid ratio, on

the extracion efficiency of polyphenols in broccoli stems.

We then carried out RSM-based optimisation to minimize the use of plant materials and solvents, save enery and time consumed during analyses, and identify an optimal factor combination that

could achieve the best polyphenol extraction efficiency. ANOVA and F-test analysis, as presented in Table 3, The regression model had an F-value of 74.61 (p < 0.0001), and the determination

coefficient R² = 0.9897, together with the lack-of-fit term value was 0.0577 (p> 0.05) show that the established quadratic equation has high significance, and this model can better reflect

the relationship between each factor and the yield. The individual factors, the interaction terms AC and AB and the coefficients of the quadratic terms (A2, B2and C2 were also found to be

significant (P < 0.05). According to the size of the F-value, the three factors A, B and C can be considered as influencing the yield of broccoli stem polyphenols. The order from largest to

smallest was C (liquid-solid ratio) > B (extraction time) > A (extraction temperature).

Two factors were utilized each time to generate 2D contour plots, representing a two-way interaction between extraction factors, to evaluate their collective effects on the response. From

the contour plots as shown in Fig. 2, the trend of significant factors and their interactions were investigated by referring to these plots. The findings revealed that the optimised

polyphenol extraction parameters were an extraction time of 40–60 min, an extraction temperature of 70–90 ℃, and a liquid-solid ratio of 30–50:1. Compared to the interaction between other

factors, the slope change of the response surface between extraction temperature and liquid-solid ratio is steeper, which exhibited a great impact on the extraction amount of broccoli stem

polyphenols, corroborating the ANOVA results.

Multiple regression analysis was employed for generating the following linear equation for predicting total polyphenol yield by extraction:

0.{\text{1}}0{\text{13A}} + 0.{\text{1741B}} + 0.{\text{1879C}} + 0.{\text{14}}00{\text{AB}} + 0.{\text{5875AC}} - 0.0{\text{712BC}} - 0.{\text{5439A}}^{{\text{2}}} -

0.{\text{1891B}}^{{\text{2}}} - 0.{\text{7}}0{\text{87C}}^{{\text{2}}}$$

where Y was the yield of polyphenols (mg/g Dw), A was the extraction temperature (℃), B was the extraction time (min), and C was the Liquid-solid ratio (mL/g).

Design-Expert was then utilized for further optimizing the variables selected based on the abovementioned results, identifying the optimal polyphenol extraction parameters of an extraction

time (A) of 54.63 min, an extraction temperature (B) of 60℃, and a liquid-solid ratio (C) of 41:1, under which a highest estimated yield of 5.12 mg/g could be obtained. Under these

extraction conditions, a polyphenol yield of 5.103 ± 0.03 mg/g was obtained by real experiments, a value that is close to the estimated yield, thereby verifying the model’s validity.

2

Contour plots generated by experimental method design for optimizing polyphenol extraction.

UPLC-Q-TOF/MS was used to further characterize polyphenolic compounds. Table 4 summarizes the MS data of fragment ion, molecular ion and polyphenol compound retention time. The exact

molecular weight patterns was used for identification, These data were compared against the corresponding published results, leading to the identification of four major polyphenol

components, namely quercetin, isochlorogenic acid, transcinnamic acid and sinapinic acid.The total ion chromatogram of a broccoli stem extract after (ChCl-Urea) DES and the representative

SIM chromatograms of the main polyphenolic compounds are shown in Figs. 3 and 4.

extract.Full size tableFig. 3

Total ion chromatogram of an extract of broccoli stem after (ChCl-Urea) DES using UHPLC-QTOF-MS in ESI − mode.

Representative SIM chromatograms obtained for an extract of broccoli stem after (ChCl-Urea) DES using UHPLC-QTOF-MS.

extracts from different solvents

Study of the effects of the in vitro antioxidant activity of different extract solvents (DES-2/H2O/70% EtOH). As shown in Fig. 5(A), the antioxidant capacity of different solvent extracts is

directly proportional to their concentration and increases with increasing concentration. At the mass concentration of 250 µg/ml, the DPPH radical scavenging capacity of 70% EtoH, DES-2 and

H2O was 79.48%, 78.12% and 34.39%, respectively. As shown in Fig. 5(B), when the different solvent extraction concentrations increased from 20 µg/mL to 250 ug/mL, the clearance of ABTS

radical from DES-2 increased from 21.50 to 82.93%, from 70%EtOH increased from 20.37 to 79.63%, and from H2O extract increased from 12.37 to 34.36%, the clearance of ABTS radical of all

three extraction solvents were proportional to the concentration. As shown in Fig. 5 (C), the Trolox molar equivalence of reduced Fe(III) was achieved as the different solvent extraction

concentrations increased from 50 µg/mL to 250 ug/mL. The results showed that DES-2 extract was the best antioxidant, followed by 70% ethanol extract. The water extract has the lowest

oxidation, the TE content is only 105 mmol/L at the concentration of 250 u g/mL. As shown in Fig. 5 (D), the total antioxidant capacity (TRAC) of the three Trolox at different solvent

extraction concentrations increased from 50 µg/mL to 250 ug/mL. DES-2 extract was 3.45 ± 0.1; 3.21 ± 0.2umol TE/L for 70% ethanol and water 1.27 ± 0.2umol TE/L; it is concluded that the

antioxidant activity of DES-2 broccoli extract was better than that of the conventional extract.The efficient enrichment of polyphenols in broccoli stems based on ChCl-urea has been further

validated by these results.

Effects of different extraction solvents on antioxidant activity. (A) The DPPH radical scavenging capacity; (B) the ABTS radical scavenging capacity; (C) Frap; (D) ORAC (Different lower-case

letters represent the same concentration there were significant differences between the different groups under the degrees (P < 0.05)).

Infinite dilution activity coefficients (\(\gamma^\infty\)) reflects the strength of interaction between solute and solvent molecules in the dissolved system, which is the solubility of

solvent for solute. The larger the concentration of solute in the solvent, the smaller the value. The calculated results of the two low eutectic solvents are shown in Table 5, DES2

(ChCl-Urea) are the lowest in both solutes, indicating that the solubility of DES2 (ChCl-Urea) for the two solutes is best. The calculated results are consistent with the experimental

results, it proves the reliability of the experimental data.

Because of the molecular specificity, σ-profile and σ-potential were used to analyze the intermolecular interactions, the results of which are shown in Figs. 6 and 7.

From Fig. 6, it can be seen that the peaks of DES2 (ChCl-Urea) and quercetin, trans-cinnamic acid overlapped more in the nonpolar region, which indicated the strong interaction between them.

It can be seen from Fig. 7 that DES2 (ChCl-Urea) has the same trend with quercetin, trans-cinnamic acid. They have higher negative values in the hydrogen bond donor region and their value

tends to increase in the hydrogen bond acceptor region, indicates that there is a strong affinity between solutes and solvents. The simulation results also reflect the reliability of the

experimental results.

σ-Profile of quercetin, trans-cinnamic acid, and 4 DESs.

σ-Potential of quercetin, trans-cinnamic acid, and 4 DESs.

This study has demonstrated the efficiency of deep eutectic solvents as green alternatives for the extraction of polyphenols from Broccoli Stem.ChCl-urea was selected from a series of

solvents for the extraction of total polyphenols from Broccoli Stem. Based on the results of the single factor experiment, RSM was used to identify the main parameters and optimise the

extraction conditions. The extraction from broccoli stem system possessed excellent antioxidant activity which was significantly higher than that from tranditonal solvent extraction methods.

The COSMO-RS calculation indicates that there is a strong affinity between solutes and solvents. Therefore, the extraction of polyphenols by DES not only enhanced the yield, but also better

retained the bioactivities of extracts. DES extraction of polyphenols from broccoli stems has the characteristics of simple synthesis, low cost, and good environmental protection extraction

effect. Overall, this study evidences that DES(ChCl-urea) provides theoretical support and technical support for its application and development in the extraction of polyphenols from

broccoli waste, valorizable for pharmaceutical, food, and cosmetic applications.

All data generated or analysed during this study are included in this published article [and its supplementary information files].The authors declare that the data supporting the findings of

this study are available within the paper and its Supplementary Information files. Should any raw data files be needed in another format they are available from the corresponding author

upon reasonable request. Source data are provided with this paper.

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This work was supported by Ningbo Public Welfare Fund Project(Grant 2021S069).

Author informationAuthors and Affiliations College of Biological and Environmental Science, Zhejiang Wanli University, No.8 South Qianhu Road, Yinzhou District, Ningbo, 315000, Zhejiang,

China

Bingqing Wang, Peiyun Chen, Huien Zhang, Yanlei Chen & Liqing Chen

AuthorsBingqing WangView author publications You can also search for this author inPubMed Google Scholar

Peiyun ChenView author publications You can also search for this author inPubMed Google Scholar

Huien ZhangView author publications You can also search for this author inPubMed Google Scholar

Yanlei ChenView author publications You can also search for this author inPubMed Google Scholar

Liqing ChenView author publications You can also search for this author inPubMed Google Scholar

Bingqing Wang, Liqing Chen, and Huien Zhang, Peiyun Chen wrote the main manuscript text and Yanlei Chen, Peiyun Chen prepared all figures. All authors reviewed the manuscript.

Corresponding author Correspondence to Peiyun Chen.

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About this articleCite this article Wang, B., Chen, P., Zhang, H. et al. Optimization of polyphenols extraction by deep eutectic solvent from broccoli stem and characterization of their

composition and antioxidative effects. Sci Rep 15, 16066 (2025). https://doi.org/10.1038/s41598-025-00632-z

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Received: 30 November 2024

Accepted: 29 April 2025

Published: 08 May 2025

DOI: https://doi.org/10.1038/s41598-025-00632-z

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KeywordsPolyphenol extractionDeep eutectic solventCompositionBroccoli stemAntioxidant activity