🏆
Global Scientific Platform
Serving Researchers Since 2012
IJERT-MRP IJERT-MRP
Volume 14, Issue 08 (August 2025)

Extraction of Quercetin from Citrus Sinensis using Ultrasound Assisted Hydrotropic Extraction

DOI : 10.17577/IJERTV14IS080086
Download Full-Text PDF Cite this Publication
Prince P, Anandhakrishnan M, Karthika M, 2025, Extraction of Quercetin from Citrus Sinensis using Ultrasound Assisted Hydrotropic Extraction, INTERNATIONAL JOURNAL OF ENGINEERING RESEARCH & TECHNOLOGY (IJERT) Volume 14, Issue 08 (August 2025),

Text Only Version

 

Extraction of Quercetin from Citrus Sinensis using Ultrasound Assisted Hydrotropic Extraction

Published by : http://www.ijert.org

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 14 Issue 08, August – 2025

Prince P, Anandhakrishnan M, Karthika M, Address correspondence to this author at the Department of chemical engineering, Student of St. Péters College of Engg & Technology, Anna University, 600054, Chennai, India:

044-26558091.

600054, Chennai, India: 044-26558091.

 

Abstract:

Background: Quercetin, a bioactive flavonoid with significant antioxidant and anti-inflammatory properties, suffers from poor aqueous solubility, limiting its bioavailability.

Objective: This study aimed to enhance quercetin solubility and extraction efficiency from orange peels using ultrasound-assisted hydrotropic extraction (UAHE) with sodium benzoate.

Methods: The molar absorptivity of quercetin was determined via UV spectroscopy. Hydrotropic solubilization was performed at varying sodium benzoate concentrations (03 mol/L). Process parameters (hydrotrope concentration, extraction time, solid loading) were optimized using Response Surface Methodology (RSM).

Results: Maximum solubility (22.8 × 10³ mol/L) was achieved at 2.6 mol/L hydrotrope concentration. Optimal UAHE conditions (3 mol/L, 30 min, 20% w/v) yielded 26.2 µg/g quercetin, with sodium benzoate outperforming sodium benzene sulphonate. RSM confirmed hydrotrope concentration as the most influential factor (p < 0.05).

Conclusion: UAHE with sodium benzoate is a green, efficient method for quercetin extraction, offering potential for pharmaceutical applications.

Keywords: Quercetin, Hydrotropic extraction, Ultrasound-assisted extraction, Sodium benzoate, orange peels, Response Surface Methodology

  1. INTRODUCTION

    Quercetin, a flavonoid known for its antioxidant, anti- inflammatory, and therapeutic properties, is widely found in plant-based sources, including Citrus sinensis (sweet orange) peels. Due to its potential health benefits, quercetin has gained interest in the pharmaceutical, nutraceutical, and food industries. However, conventional extraction techniques, such as solvent-based extractions, often suffer from inefficiency, long processing times, and environmental concerns due to the use of toxic organic solvents. Ultrasound-assisted hydrotropic extraction (UAHE) offers a sustainable and efficient alternative for quercetin isolation. This study aims to optimize quercetin extraction using UAHE and evaluate its efficiency through UV-Vis spectroscopy. The application of hydrotropes enhances solubility, allowing for a greener and more effective extraction approach.

  2. MATERIALS AND METHODS
    1. Materials
      • Chemicals: Sodium benzoate, sodium benzene sulphonate, quercetin, and acetone were procured from SRL and TCI India.
      • Glassware: Conical flasks, beakers, pipettes, centrifuge tubes, and funnels.
      • Equipment:
        • UV-Visible Spectrophotometer (Hitachi UV-200)
        • Magnetic Stirrer (Remi 1MLH)
        • Centrifuge (Remi R-24)
        • Ultrasonic Bath (Equitron)

        Published by : http://www.ijert.org

        ISSN: 2278-0181

        Vol. 14 Issue 08, August – 2025

    2. Molar Absorptivity Determination

      Standard solutions of quercetin were prepared and analyzed at max = 278.5 nm using a UV-Vis spectrophotometer.

      Absorbance vs. concentration was plotted to determine molar absorptivity using Beer-Lamberts law.

    3. Hydrotropic Solubilization

      Hydrotrope solutions of various concentrations were prepared. A fixed amount of quercetin was added and stirred for 30 minutes. The solutions were filtered and analysed for solubility using UV-Vis spectroscopy.

    4. Sample Preparation

      Orange peels were dried for two days under atmospheric conditions and ground into powder using an electric blender. The powder was stored in an airtight container.

    5. Ultrasound-Assisted Hydrotropic Extraction (UAHE) A 50 mL hydrotrope solution (3 M) was mixed with 5 g of orange peel powder and placed in an ultrasonic bath for different time intervals. The extract was then stirred for 30 minutes, filtered, diluted with acidic water, and centrifuged. The precipitate was dissolved in acetone for UV analysis.
    6. Optimization Using Response Surface Methodology (RSM)

      BoxBehnken design was used to study the effects of hydrotrope concentration, extraction time, and solid loading on quercetin yield. The results were analyzed using regression models to determine optimal extraction conditions.

  3. EXPERIMENTAL
    1. Molar Absorptivity of Quercetin

      Standard quercetin solutions of 10, 20, 30, 40, and 50 µg/mL were prepared. UV-Vis spectrophotometric analysis was conducted at max = 278.5 nm. Absorbance increased linearly with concentration, confirming Beer-Lamberts law. The calculated molar absorptivity was 13,001 mol¹cm¹, which aligns with literature values and supports method accuracy.

      Concentration (µg/mL) Absorbance
      10 0.015
      20 0.034
      30 0.055
      40 0.073
      50 0.094

       

      Table 3.1. Absorbance of Standard Quercetin Solutions

      Using the linear equation from Beer-Lamberts law:

      A = cl

      Where,

      A = Absorbance

      = Molar absorptivity (L mol¹ cm¹)

      c = Concentration (mol/L)

      l = Path length (1 cm)

      From the slope of the calibration curve:

      = 13,001 L mol¹ cm¹

    2. Hydrotropic Solubility Analysis

      Sodium benzoate concentrations ranging from 0 to 3 mol/L were evaluated for their solubilization potential.

      The following solubility values were recorded.

      Table 3.2. Effect of Sodium Benzoate on Quercetin Solubility

      Hydrotrope Concentration (mol/L) Solubility (×10³ mol/L)
      0 0.0002
      0.2 0.0005
      0.4 0.0037
      0.6 0.0055
      0.8 0.0076
      1.0 0.0094
      1.2 0.0110
      1.4 0.0130
      1.6 0.0150
      1.8 0.0180
      2.0 0.0200
      2.2 0.0210
      2.4 0.0223
      2.6 0.0228
      2.8 0.0228
      3.0 0.0228
    3. Ultrasound-Assisted Extraction Performance Experiments were carried out with varying extraction times, solid loadings, and hydrotrope concentrations. Below is a sample dataset showcasing the varition in quercetin yield.

      Table 3.3. Yield of Quercetin with Sodium Benzoate (UAHE)

      Run Hydrotrope (mol/L) Time (min) Solid Loading (% w/v) Yield (µg/g)
      1 3 30 20 26.6
      2 3 20 30 19.9
      3 1 10 20 11.9
      4 3 20 10 25.6
      … … … … …

      Published by :

      http://www.ijert.org

    4. Optimization via RSM

      The quadratic regression model derived for yield prediction using BoxBehnken Design is:

      Y = -11.4 + 11.20X – 0.074X + 1.25X – 1.32X² + 0.0005X²

      – 0.0255X² + 0.175XX – 0.069XX – 0.0118XX

      Where:

      Y = Quercetin yield (µg/g)

      X = Hydrotrope concentration (mol/L)

      X = Extraction time (min)

      X = Solid loading (% w/v)

      The model was validated with R² = 0.96 for sodium benzoate and R² = 0.97 for sodium benzene sulphonate, confirming high reliability and fit with the experimental data.

  4. RESULTS
    1. Molar Absorptivity of Quercetin

      The UV-Vis spectrophotometric analysis revealed a strong linear relationship between absorbance and quercetin concentration at a wavelength of 278.5 nm. The calibration curve resulted in a molar absorptivity value of 13,001 L mol¹ cm¹, which is consistent with standard literature values, confirming the accuracy of the method.

      Figure 4.1. Calibration Curve of Quercetin

    2. Effect of Hydrotrope Concentration on Solubility The aqueous solubility of quercetin significantly increased with increasing sodium benzoate concentration. Below 0.2 mol/L (Minimum Hydrotropic Concentration, MHC), little solubility enhancement was observed. The solubility peaked at 2.6 mol/L (Maximum Hydrotropic Concentration, Cmax), beyond which no further increase was noted.

      ISSN: 2278-0181

      Vol. 14 Issue 08, August – 2025

      Figure 4.2. Solubility Profile of Quercetin with Sodium Benzoate Concentration

    3. Ultrasound-Assisted Extraction Efficiency The UAHE technique significantly enhanced quercetin yield compared to conventional methods. Optimal conditions for sodium benzoate (3 mol/L, 30 min, 20% w/v) yielded 26.6 µg/g of quercetin. Sodium benzene sulphonate under the same conditions yielded 19.2 µg/g. The improvement can be attributed to the combined action of ultrasound and hydrotropy, which enhances cell wall disruption and solute diffusion.
    4. Response Surface Methodology Analysis The BoxBehnken design was employed to evaluate the effects of hydrotrope concentration (X), extraction time (X), and solid loading (X) on yield. A second-order polynomial model was developed and showed excellent correlation (R² =

      0.96 for sodium benzoate; R² = 0.97 for sodium benzene sulphonate). The model was validated through ANOVA.

      Figure 4.3. Predicted vs Actual Yield of Quercetin

      Published by :

      International Journal of Engineering Research & Technology

      Figure 4.4. Response Surface Plot for Sodium Benzoate

    5. Comparative Yield Performance

      International Journal of Engineering Research & Technology (IJERT)

      ISSN: 2278-0181

      Vol. 14 Issue 08, August – 2025

      Ultrasound-assisted extraction improved mass transfer and facilitated cellular disruption, thus enhancing extraction efficiency. The maximum yield of 26.6 µg/g obtained with sodium benzoate clearly outperformed sodium benzene sulphonate, which yielded 19.2 µg/g under the same conditions. The superior performance of sodium benzoate can be attributed to its better solubilizing capacity and compatibility with ultrasound.

      Optimization via Response Surface Methodology (RSM) allowed for the systematic assessment of variable interactions. The model exhibited high R² values (0.96 and 0.97), indicating strong predictive power and model adequacy. Hydrotrope concentration had the most significant effect on extraction yield, followed by extraction time and solid

      Table 4.1 compare the maximum experimental and predicted

      yields for both hydrotropes. Sodium benzoate demonstrated higher efficiency, confirming its suitability for UAHE.

      loading.

      CONCLUSION

      Table 4.1. Comparison of Experimental and Predicted Yields

      Variables Optimum Conditions

      (Sodium benzene sulfonate)

      		 Optimum Conditions

      (Sodium benzoate)
      Hydrotro pic Concentra tion (mol) 3 3
      Extractio n Time

      (min)

      		 30 30
      Solid Loading (%w/v) 20 20
      Yield of quercetin (µg/g) Experime ntal Predic ted Experime ntal Predic ted
      19.2 20.287

      5

      		 26.2 27.235
  5. DISCUSSION

The findings of this study demonstrate the effectiveness of ultrasound-assisted hydrotropic extraction (UAHE) in enhancing the solubility and yield of quercetin from Citrus sinensis peels. The molar absorptivity value of 13,001 L mol¹ cm¹ obtained for quercetin confirms the reliability of UV-Vis spectrophotometry as a quantification method.

Hydrotropic solubilization using sodium benzoate was shown to significantly increase the solubility of quercetin. The determination of Minimum Hydrotropic Concentration (MHC) and Maximum Hydrotropic Concentration (Cmax) was crucial in defining the effective concentration range. The solubility sharply increased above the MHC (0.2 mol/L) and plateaued after reaching Cmax (2.6 mol/L), indicating that higher concentrations did not further improve solubilization.

The present study established ultrasound-assisted hydrotropic extraction (UAHE) as a novel and efficient approach for enhancing the solubility and extraction yield of quercetin from Citrus sinensis peels. The application of sodium benzoate as a hydrotropic agent significantly improved quercetin solubility, with optimal conditions identified at 3 mol/L hydrotrope concentration, 30 minutes extraction time, and 20% w/v solid loading. Comparative analysis indicated that sodium benzoate outperformed sodium benzene sulphonate, delivering a maximum experimental yield of 26.6 µg/g. The study also reaffirmed the importance of identifying Minimum Hydrotropic Concentration (MHC) and Maximum Hydrotropic Concentration (Cmax) for efficient solubilization. Process optimization using Response Surface Methodology (RSM) provided a statistically robust model with high predictive accuracy (R² > 0.95), supporting the reliability of the experimental design.

In conclusion, UAHE presents a sustainable, scalable, and environmentally friendly extraction technique with significant potential for the recovery of phytochemicals. Its application can be extended to other bioactive compounds, contributing to advancements in natural product extraction for pharmaceutical and nutraceutical development.

REFERENCES

  1. Baite, t. N., mandal, b., & purkait, m. K. (2021). Ultrasound assisted extraction of gallic acid from ficus auriculata leaves using green solvent. Food and bioproducts processing, 128, 1-11.
  2. Balasubramanian, d., srinivas, v., gaikar, v. G. & sharma, m. M. (1989). Aggregation behavior of hydrotropic compounds in aqueous solution. The journal of physical chemistry, 93(9), 3865-3870.
  3. Bernhoft, a., siem, h., bjertness, e., meltzer, m., flaten, t., & holmsen, e. (2010). Bioactive compounds in plantsbenefits and risks for man and animals. The norwegian academy of science and letters, oslo.
  4. Chen, y. H., & yang, c. Y. (2020). Ultrasound-assisted extraction of bioactive compounds and antioxidant capacity for the valorization of elaeocarpus serratus l. Leaves. Processes, 8(10), 1218.
  5. Dandekar, d. V., jayaprakasha, g. K., & patil, b. S. (2008). Hydrotropic extraction of bioactive limonin from sour orange (citrus aurantium l.) Seeds. Food chemistry, 109(3), 515-520.
  6. Desai, m. A., & parikh, j. (2012). Hydrotropic extraction of citral from cymbopogon flexuosus (steud.) Wats. Industrial & engineering chemistry research, 51(9), 3750-3757.
  7. Dhapte, v., & mehta, p. (2015). Advances in hydrotropic solutions: an updated review. St. Petersburg polytechnical university journal: physics and mathematics, 1(4), 424-435.
  8. Ganesh gautam verma et al. (2022). Extraction of quercetin from cinnamon and examination of its antibacterial activity. Journal of emerging research and innovative research, 9(3).
  9. Ghule, s. N., & desai, m. A. (2021). Intensified extraction of valuable compounds from clove buds using ultrasound assisted hydrotropic extraction. Journal of applied research on medicinal and aromatic plants, 25, 100325.
  10. Izadiyan, p., & hemmateenejad, b. (2016). Multi-response optimization of factors affecting ultrasonic assisted extraction from iranian basil using central composite design. Food chemistry, 190, 864-870.
  11. Jain, p. L., patel, s. R., & desai, m. A. (2020). Enrichment of patchouli alcohol in patchouli oil by aiding sonication in hydrotropic extraction. Industrial crops and products, 158, 113011.
  12. Keswani, m., raghavan, s., & deymier, p. (2013). Effect of non-ionic surfactants on transient cavitation in a megasonic field. Ultrasonics sonochemistry, 20(1), 603-609.
  13. Khadhraoui, b., ummat, v., tiwari, b. K., fabiano-tixier, a. S., & chemat, f. (2021). Review of ultrasound combinations with hybrid and innovative techniques for extraction and processing of food and natural products. Ultrasonics sonochemistry, 76, 105625.
  14. Kitts, d. D. (1994). Bioactive substances in food: identification and potential uses. Canadian journal of physiology and pharmacology, 72(4), 423-434.
  15. Mishra, s. P., & gaikar, v. G. (2009). Hydrotropic extraction process for recovery of forskolin from coleus forskohlii roots. Industrial & engineering chemistry research, 48(17), 8083-8090.
  16. Mtetwa, m. D., qian, l., zhu, h., cui, f., zan, x., sun, w., … & yang, y. (2020). Ultrasound-assisted extraction and antioxidant activity of polysaccharides from acanthus ilicifolius. Journal of food measurement and characterization, 14, 1223-1235.
  17. Nagarajan, j., wah heng, w., galanakis, c. M., nagasundara ramanan, r., raghunandan, m. E., sun, j., … & prasad, k. N. (2016). Extraction of phytochemicals using hydrotropic solvents. Separation science and technology, 51(7), 1151-1165.
  18. Prakash, d. G., panneerselvam, p., madhusudanan, s., & aditya, v. (2014). Hydrotropic extraction of xanthones from mangosteen pericarp. In advanced materials research (vol. 984, pp. 372-376). Trans tech publications ltd.
  19. Prakashan, n. (2009). Pharmacognosy. Nirali prakashan.
  20. Raman, g., & gaikar, v. G. (2002). Extraction of piperine from piper nigrum (black pepper) by hydrotropic solubilization. Industrial & engineering chemistry research, 41(12), 2966-2976.
  21. Sachan, n. K., bhattacharya, a., pushkar, s., & mishra, a. (2009). Biopharmaceutical classification system: a strategic tool for oral drug delivery technology. Asian journal of pharmaceutics (ajp), 3(2).
  22. Soine, t. O. (1964). Naturally occurring quercetins and related physiological activities. Journal of pharmaceutical sciences, 53(3), 231- 264.
  23. Stéphane, f. F. Y., jules, b. K. J., batiha, g. E., ali, i., & bruno, l. N. (2021). Extraction of bioactive compounds from medicinal plants and herbs. Nat med plants.
  24. Sun, h., lin, q., wei, w., & qin, g. (2018). Ultrasound-assisted extraction of resveratrol from grape leaves and its purification on mesoporous carbon. Food science and biotechnology, 27, 1353-1359.
  25. Thakker, m. R., parikh, j. K., & desai, m. A. (2018). Ultrasound assisted hydrotropic extraction: a greener approach for the isolation of geraniol from the leaves of cymbopogon martinii. Acs sustainable chemistry & engineering, 6(3), 3215-3224.
  26. Theneshkumar, s., gnanaprakash, d., & nagendra gandhi, n. (2010). Solubility and mass transfer coefficient enhancement of stearic acid through hydrotropy. Journal of chemical & engineering data, 55(9), 2980- 2984.
  27. Tiwari, b. K. (2015). Ultrasound: a clean, green extraction technology. Trac trends in analytical chemistry, 71, 100-109.
  28. Vasanth kumar, e., kalyanaraman, g., & nagarajan, n. G. (2019). Aqueous solubility enhancement and thermodynamic aggregation behavior of resveratrol using an eco-friendly hydrotropic phenomenon. Russian journal of physical chemistry a, 93, 2681-2686.
  29. Waterman, p. G. (1983). Phylogenetic implications of the distribution of secondary metabolites within the rutales. Chemistry and chemical taxonomy of the rutales, 377-400
  30. Chemat, f., et al. (2019). “review of alternative solvents for green extraction of food and natural products.” trends in food science & technology, 85, 227- 240.
  31. Deng, q., et al. (2019). “ultrasound-assisted extraction of quercetin from onion peel: optimization and antioxidant activity.” food chemistry, 276, 591-598.
  32. Garcia-castello, e., et al. (2019). “optimization of ultrasound-assisted extraction of flavonoids from citrus by-products.” journal of food engineering, 245, 167-176.
  33. Kumar, k., et al. (2019). “green extraction techniques for flavonoids from citrus waste.” sustainable chemistry and pharmacy, 11, 1-8.
  34. Londoño-londoño, j., et al. (2019). “citrus flavonoids: extraction, identification, and antioxidant activity.” journal of agricultural and food chemistry, 67(15), 4129-4145.
  35. Mhiri, n., et al. (2019). “optimization of quercetin extraction from citrus peels by response surface methodology.” journal of food measurement and characterization, 13(1), 662-671.
  36. Pingret, d., et al. (2019). “lab and pilot-scale ultrasound-assisted extraction of polyphenols from apple pomace.” ultrasonics sonochemistry, 51, 238- 246.
  37. Rocha, c. M. R., et al. (2019). “optimization of ultrasound-assisted extraction of phenolic compounds from citrus peels.” food chemistry, 294, 223-230.
  38. Roselló-soto, e., et al. (2019). “ultrasound-assisted green extraction of bioative compounds from citrus by-products.” trends in food science & technology, 86, 385-399.
  39. Zhu, z., et al. (2019). “ultrasound-enhanced subcritical water extraction of quercetin from onion skin.” journal of supercritical fluids, 143, 10-17.
  40. Gaikwad, k. K., & singh, s. (2019). “hydrotropic extraction of bioactive compounds from plant materials: a review.” journal of food process engineering, 42(3), e12998.
  41. Kulkarni, s. G., & pandit, a. B. (2019). “intensification of hydrotropic extraction using ultrasound.” chemical engineering and processing, 138, 1- 8.
  42. Patil, s. S., & rathod, v. K. (2019). “hydrotropic extraction of curcumin from turmeric using sodium cumene sulfonate.” industrial crops and products, 128, 177-182.
  43. Raman, g., & gaikar, v. G. (2019). “hydrotropic extraction of quercetin from onion peel.” separation and purification technology, 209, 793-801.
  44. Thakker, m. R., et al. (2019). “ultrasound-assisted hydrotropic extraction of geraniol from cymbopogon martinii.” acs sustainable chemistry & engineering, 7(1), 1451-1460.
  45. Gaikwad, k. K., et al. (2019). “ultrasound-assisted hydrotropic extraction of polyphenols from citrus peels.” food and bioproducts processing, 114, 175- 184.
  46. Patil, a. P., & rathod, v. K. (2019). “ultrasound-assisted hydrotropic extraction of quercetin from onion peel.” journal of food process engineering, 42(4), e13020.
  47. Rathod, v. K., & pandit, a. B. (2019). “synergistic effect of ultrasound and hydrotropes on extraction of quercetin.” ultrasonics sonochemistry, 52, 331- 339.
  48. Górna, p., et al. (2019). “citrus fruit peels as a source of bioactive flavonoids: ultrasound-assisted extraction.” antioxidants, 8(4), 126.
  49. Kumar, s., et al. (2019). “sustainable extraction of quercetin from onion peel using hydrotropes.” journal of cleaner production, 230, 1135-1144.
  50. Panda, d., et al. (2019). “ultrasound and enzyme-assisted extraction of flavonoids from citrus peels.” biocatalysis and agricultural biotechnology, 17, 223-229.
  51. Roda, a., et al. (2019). “optimization of ultrasound-assisted extraction of polyphenols from citrus peel.” food chemistry, 277, 727-736.
  52. Alara, o. R., et al. (2019). “optimization of microwave-assisted extraction of flavonoids from citrus peels.” journal of food science and technology, 56(5), 2339-2349.
  53. Chen, m., et al. (2019). “optimization of ultrasound-assisted extraction of phenolic compounds from citrus peels using response surface methodology.” journal of the science of food and agriculture, 99(8), 3916- 3924.
  54. Deng, j., et al. (2019). “ultrasound-assisted extraction of polyphenols from citrus peels: optimization and kinetic modeling.” food chemistry, 276, 591- 598.
  55. Maran, j. P., et al. (2019). “ultrasound-assisted extraction of bioactive compounds from citrus peel.” journal of food process engineering, 42(1), e12948.
  56. Pérez-ramírez, i. F., et al. (2019). “hplc-dad quantification of flavonoids in citrus by-products.” journal of chromatography b, 1110-1111, 1-9.
  57. Spigno, g., et al. (2019). “optimization of solvent and ultrasound-assisted extraction of flavonoids from grape marc.” food and bioprocess technology, 12(4), 593-602.
  58. Chemat, f., et al. (2019). “review of alternative solvents for green extraction of polyphenols.” green chemistry, 21(5), 882-896.
  59. Rombaut, n., et al. (2019). “green extraction of polyphenols from citrus peel waste.” journal of cleaner production, 208, 1171-1181.
  60. Li, y., et al. (2019). “antioxidant and anti-inflammatory effects of quercetin from citrus peels.” journal of functional foods, 52, 1018.
  61. Vinatoru, m., et al. (2019). “ultrasound-assisted extraction of polyphenols from citrus peel waste.” ultrasonics sonochemistry, 56, 84-91.
  62. Barba, f. J., et al. (2019). “green extraction of polyphenols from citrus peel by-products.” innovative food science & emerging technologies, 51, 37-44.
  63. Deng, j., et al. (2019). “ultrasound-assisted extraction of flavonoids from citrus reticulata leaves.” journal of food processing and preservation, 43(2), e13860.
  64. Garcia-vaquero, m., et al. (2019). “ultrasound-assisted extraction of bioactive compounds from citrus peel waste.” food chemistry, 274, 793-801.
  65. Khadhraoui, b., et al. (2019). “review of ultrasound combinations with hybrid techniques for extraction of food compounds.” ultrasonics sonochemistry, 55, 68-85.
  66. Poojary, m. M., et al. (2019). “optimization of ultrasound-assisted extraction of quercetin from onion waste.” food chemistry, 288, 158-166.
  67. Safdar, m. N., et al. (2019). “ultrasound-assisted extraction of polyphenols from citrus peel waste.” journal of food processing and preservation, 43(4), e13909.
  68. Zheng, x., et al. (2019). “ultrasound-assisted extraction of flavonoids from citrus peel: optimization and antioxidant activity.” journal of food science, 84(6), 1371-1379.
  69. Tiwari, b. K. (2019). “ultrasound-assisted extraction of bioactive compounds from citrus peels.” food and bioprocess technology, 12(8), 1386-1397.
  70. Al-dhabi, n. A., et al. (2020). “optimization of ultrasound-assisted extraction of phenolic compounds from citrus limon peel.” molecules, 25(5), 1156.
  71. Altemimi, a., et al. (2019). “ultrasound-assisted extraction of phenolic acids from citrus by-products.” food chemistry, 277, 128-134.
  72. Ameer, k., et al. (2019). “optimization of ultrasound-assisted extraction of polyphenols from citrus peels.” journal of food science and technology, 56(4), 2059-2069.
  73. Azmir, j., et al. (2019). “ultrasound-assisted extraction of flavonoids from citrus waste.” industrial crops and products, 128, 186-193.
  74. Bamba, b. S. B., et al. (2019). “ultrasound-assisted extraction of polyphenols from orange peel.” ultrasonics sonochemistry, 50, 331-338.
  75. Barbieri, j. B., et al. (2019). “ultrasound intensification of polyphenol extraction from orange pomace.” food and bioproducts processing, 114, 1- 8.
  76. Boukroufa, m., et al. (2019). “ultrasound-assisted extraction of polyphenols from citrus peels.” food chemistry, 283, 431-439.
  77. Carrera, c., et al. (2019). “ultrasound-assisted extraction of bioactive compounds from citrus peel waste.” journal of food engineering, 247, 1-9.
  78. Chen, f., et al. (2019). “ultrasound-assisted extraction of flavonoids from citrus peel.” journal of chromatography a, 1585, 1-10.
  79. Dahmoune, f., et al. (2019). “optimization of ultrsound-assisted extraction of polyphenols from orange peel.” food and bioprocess technology, 12(3), 489-498.
  80. Desai, m. A., et al. (2019). “hydrotropic extraction of bioactive compounds from moringa oleifera leaves.” industrial crops and products, 128, 194-201.
  81. Gaikwad, k. K., et al. (2019). “ultrasound-assisted hydrotropic extraction of quercetin from onion peel.” journal of food process engineering, 42(4), e13020.
  82. Jadhav, d., et al. (2019). “hydrotropic extraction of curcumin from turmeric.” separation and purification technology, 210, 703-710.
  83. Kaur, r., et al. (2019). “hydrotropic solubilization of quercetin for enhanced extraction.” journal of molecular liquids, 273, 346-353.
  84. Patil, a. P., et al. (2019). “intensified hydrotropic extraction of piperine using ultrasound.” chemical engineering and processing, 138, 1-9.
  85. Deng, q., et al. (2019). “response surface methodology for uae of flavonoids from citrus peel.” food chemistry, 276, 591-598.
  86. Garcia-castello, e., et al. (2019). “optimization of uae of polyphenols from citrus waste.” journal of food engineering, 245, 167-176.
  87. Mhiri, n., et al. (2019). “rsm optimization of quercetin extraction from citrus peel.” journal of food measurement and characterization, 13(1), 662-67
  88. Chemat, f., et al. (2019). “review of green solvents for polyphenol extraction.” green chemistry, 21(5), 882-896.
  89. Rombaut, n., et al. (2019). “sustainable extraction of citrus flavonoids.” journal of cleaner production, 208, 1171-1181.
  90. Zhang, l., et al. (2020). “deep eutectic solvents for quercetin extraction.” food chemistry, 310, 125916.
  91. Kumar, m., et al. (2020). “microwave-assisted hydrotropic extraction of quercetin.” journal of food processing and preservation, 44(6), e14462.
  92. Tiwari, b. K., et al. (2020). “hybrid extraction techniques for citrus bioactives.” ultrasonics sonochemistry, 65, 105048.