ULTRASONIC EXTRACTION

What is ultrasound-assisted extraction?

In essential oil production, the review by Youchret-Zallez et al. (2026) writes, ultrasound-assisted extraction (UAE) is frequently used as a pretreatment before hydrodistillation or in combination with other techniques, rather than as a stand-alone method for obtaining classical distilled essential oils. The same review considers UAE mainly as a pretreatment or intensification strategy in essential oil recovery.

Which conditions change the result?

The review by Youchret-Zallez et al. (2026) describes UAE performance as strongly condition-dependent, its outcome depending on ultrasound frequency, amplitude, real acoustic power delivered to the medium, sonication time, temperature, solvent properties, solvent-to-solid ratio, particle size, reactor geometry and sample loading. According to the review, excessive sonication or poorly controlled temperature “may” alter sensitive constituents, while inefficient acoustic-field distribution “may” reduce reproducibility.

According to Youchret-Zallez et al., UAE can reduce extraction time, solvent use and energy demand, particularly when used as a pretreatment for hydrodistillation or combined with green solvents.

What did one study on Tribute citrus peel measure?

In the study by Li et al. (2022), Tribute citrus (TC) berries were harvested in October 2020 in Wuming, China. The study proposed traditional hydrodistillation (HD) and ultrasound-assisted pretreatment extraction (UAPE) to obtain essential oil from TC peels. Li et al. describe Tribute citrus as a hybrid variety of orange and tangerine, belonging to the genus Citrus of the Rutaceae family and mainly distributed in the south of China.

The peels were detached manually, dried in an oven at 37 °C for 72 h, their moisture content measured with a water activity meter at 4.12 ± 0.16 %, then pulverized by a mill through a 60 mesh sieve. In the distillation described by the authors, ten grams of fine homogenized TC powder were mixed with a 1.5 % sodium chloride aqueous solution, and the whole distillation was carried out until there was no more significant increase in the volume of essential oil. The yield was determined per gram of raw material (dry weight), with three replicates for each treatment.

Which conditions did the study retain?

For traditional hydrodistillation (HD), Li et al. give as optimal conditions a solvent-solid ratio of 20.32:1, an extraction time of 125.38 min and a sodium chloride concentration of 1.15 %, for a predicted yield of 85.69 mg/g of essential oil. The yield obtained was 85.67 mg/g, which the authors describe as similar to the predicted value. Examining the effect of ultrasound time on the essential oil yield, the authors obtained the maximum yield at 20 min, the yield then decreasing as ultrasound time extended. For the ultrasound-assisted extraction process, the optimal conditions were a solvent-solid ratio of 20.09:1, 20.7 min of ultrasound, 60.04 min of extraction and a sodium chloride concentration of 1.62 %, yielding 115.072 mg/g of essential oil. The verification experiment, carried out at a 20:1 solvent-solid ratio, 1.62 % sodium chloride, 20.7 min of ultrasound and 60 min of extraction, gave 114.02 mg/g, which the authors describe as similar to the predicted value.

How do the two methods compare in this study?

Li et al. write that, compared with the extraction yield of traditional HD (85.67 ± 0.73 mg/g), higher essential oil yields were acquired by the proposed ultrasound-assisted process, abbreviated UAPE (114.02 ± 2.79 mg/g), in a shorter extraction time. In the same comparison, the extraction time is given as 120 min for HD and 80 min for UAPE. The optimal conditions stated in the same paper include 125.38 min of extraction for HD, and 20.7 min of ultrasound with 60.04 min of extraction for the ultrasound-assisted process.

A total of 28 constituents were identified by GC-MS. The percentages for HD and UAPE were respectively 90.99 and 91.16 % for cyclic monoterpenes, 5.09 and 4.94 % for acyclic monoterpenes, 0.45 and 0.47 % for acyclic sesquiterpenes, 1.17 and 1.08 % for aldehydes, and 0.59 and 0.56 % for alcohols. d-Limonene was the predominant constituent, at 86.38 and 86.75 %.

What did one study on celery seeds measure?

In the study by Zorga et al. (2020), the experiments used dried celery seeds, Apium graveolens L., that showed no germination power and were industrial waste. The raw material was donated by the manufacturer as part of a cooperation with a Polish seed company. Sonication of 100 g of ground celery seeds was conducted in a UP400S sonicator (400 W, 24 kHz) with a sound protection box, an electronic timer controlling the acoustic irradiation duration and a titanium sonotrode. The application of ultrasound followed an L9 orthogonal array. The essential oils were extracted by hydrodistillation in a modified Deryng apparatus, with 1000 mL of distilled water per 100 g of celery seeds. The control sample was the essential oil from untreated seeds, without ultrasound. The yield was calculated as an average of three hydrodistillations, and the percentage increase of yield by a formula in which YUAH is the yield obtained by ultrasound-assisted hydrodistillation and YHD the yield obtained by hydrodistillation.

Which yields did the study report?

At the individual working levels, the essential oil yield ranged from 1.456 ± 0.011 to 1.978 ± 0.048 g per 100 g of seeds. Additional experiments with sonication times of 50, 70 and 90 min, under optimum conditions of the other parameters, gave 2.15 ± 0.032, 2.07 ± 0.06 and 2.04 ± 0.06 g per 100 g of seeds. The authors considered 50 min the optimal sonication time, due to the lack of significant performance improvement. The optimum conditions they report for celery seeds pre-treated with ultrasound were a sonication time of 50 min, a pulse range of 0.5, a power control amplitude of 60 % and a water content of 700 mL. The authors give 2.23 g of essential oil as the theoretical yield under optimal conditions, and 2.15 ± 0.032 g per 100 g of seeds as the experimental yield of seeds sonicated under these conditions. They report that the efficiency increased by 48.3 %.

What was the composition of the oil?

In the essential oil obtained by ultrasonic hydrodistillation, 30 compounds were identified, constituting 99 % of the composition (GC-MS, NIST library). The principal constituents were limonene (76.9 %), β-selinene (9.7 %), sedanenolide (3.4 %), 3-butylphthalide (3.6 %) and α-selinene (1.4 %). Monoterpenes (78.4 %) were the predominant group, followed by sesquiterpenes (11.1 %) and hydrocarbons (7.8 %).

What did one study on spearmint measure?

In the study by Moradi-Sadr et al. (2023), spearmint plants, Mentha spicata L., were cultivated at the research farm of the Faculty of Agriculture, Tarbiat Modares University, harvested at the vegetative stage and shade dried in the drying room at 25 °C for one week. The essential oil of the treated samples was immediately extracted by hydrodistillation, 30 g of dried spearmint being hydrodistilled in a Clevenger-type apparatus for 3 h per sample. The study used three pretreatments, ultrasonic bath (UB), water to material ratio with ultrasonic bath (W/M-UB) and cold plasma with ultrasonic bath (CP-UB), in three experiments designed with the central composite design of response surface methodology. The treatments covered UB temperature (30 to 80 °C) and duration (1 to 30 min), cold plasma power (15 to 24 kV) and water/material ratio (10 to 40), before hydrodistillation in a Clevenger apparatus. The UB pretreatment was applied with an Elmasonic S 60 H processor, operating at 220 to 240 V.

The optimized conditions were a UB temperature of 37.3 °C and a UB time of 5.2 min for UB; a W/M ratio of 33.9, a UB temperature of 69.9 °C and a UB time of 6.9 min for W/M-UB; and, written without units, a CP power of 22.176, a UB temperature of 40.135 and a UB time of 24.122 for CP-UB.

Which yields did the study report?

The essential oil yield of the control sample (conventional hydrodistillation) was 0.61 %, against 0.73 %, 1.26 % and 0.95 % for the UB, W/M-UB and CP-UB treatments. In the authors’ words, the three pretreatments in optimized conditions “raised SEO yield to 119.7%, 206.6%, and 155.7% in comparison to the control sample”. The authors write that increasing the UB duration and the cold plasma power led to an increase in the amount of extracted essential oil, while increasing the UB temperature led to a decrease, and that the W/M ratio had an inverse correlation with the yield.

What changed in the composition?

According to Moradi-Sadr et al., the analysis of the essential oils identified 45 compounds. Oxygenated monoterpenes ranged from 71.07 % in the control to 77.52 % in the W/M-UB treated sample, followed by monoterpene hydrocarbons, from 7.46 % in the W/M-UB treated sample to 14.71 % in the control. According to the authors, the content of oxygenated monoterpenes was slightly higher than in the control in all three optimized conditions, while monoterpene hydrocarbon percentages were lower than the control. The carvone to limonene ratio, used as a qualitative indicator, was higher in the treated samples (4.51 for UB and 4.47 for CP-UB) than in the control (3.59). According to the authors, this ratio indicated that the applied treatments improved the quality of the spearmint essential oil.

What did one study on sage, rosemary and bay laurel measure?

In the study by Miljanović et al. (2020), the plants were sage, Salvia officinalis L., rosemary, Salvia rosmarinus Spenn. (Rosmarinus officinalis L. in the study), and bay laurel, Laurus nobilis L.; for each protocol, 20 g of milled plant material was mixed with 250 mL of MiliQ water. For the ultrasound pretreatment (HD-U), the plant material in water was treated with a 14 mm diameter ultrasonic probe at 30 % of the maximal ultrasonic power for 10 min, then hydrodistilled in a Clevenger apparatus for 2.5 h. Hydrodistillation without pretreatment was performed as a negative control, and every extraction was done once. Compared with the control experiment, the ultrasound pretreatment caused a 50 % improvement in essential oil yield for sage and rosemary and 60 % for bay laurel, similar to the results of reflux-assisted extraction. The authors write that they have demonstrated the beneficial effect of ultrasound pretreatment on the overall extraction efficiency.

References

• Youchret-Zallez O.B., Spigarelli R., Kouki A., Mbirki L., Ben-Attia M. et al., « Essential Oil Quality in Medicinal and Aromatic Plants: Linking Plant Biosynthesis, Matrix Selection and Extraction Strategy », Plants 2026;15(18):2771, doi:10.3390/plants15182771 — https://www.ebi.ac.uk/europepmc/webservices/rest/PMC13610020/fullTextXML
• Li G., Liu S., Zhou Q., Han J., Qian C. et al., « Effect of Response Surface Methodology-Optimized Ultrasound-Assisted Pretreatment Extraction on the Composition of Essential Oil Released From Tribute citrus Peels », Frontiers in Nutrition 2022;9:840780, doi:10.3389/fnut.2022.840780 — https://www.ebi.ac.uk/europepmc/webservices/rest/PMC9097513/fullTextXML
• Zorga J., Kunicka-Styczyńska A., Gruska R., Śmigielski K., « Ultrasound-Assisted Hydrodistillation of Essential Oil from Celery Seeds (Apium graveolens L.) and Its Biological and Aroma Profiles », Molecules 2020;25(22):5322, doi:10.3390/molecules25225322 — https://www.ebi.ac.uk/europepmc/webservices/rest/PMC7698019/fullTextXML
• Moradi-Sadr J., Ebadi M.T., Ayyari M., Ghomi H., « Optimization of ultrasonic Bath and cold plasma pre-treatments in the spearmint essential oil isolation process », Food Science & Nutrition 2023;11(4):1904-1915, doi:10.1002/fsn3.3224 — https://www.ebi.ac.uk/europepmc/webservices/rest/PMC10084965/fullTextXML
• Miljanović A., Bielen A., Grbin D., Marijanović Z., Andlar M. et al., « Effect of Enzymatic, Ultrasound, and Reflux Extraction Pretreatments on the Chemical Composition of Essential Oils », Molecules 2020;25:4818, doi:10.3390/molecules25204818 — https://www.ebi.ac.uk/europepmc/webservices/rest/PMC7587977/fullTextXML
• Govaerts R. (ed.), World Checklist of Vascular Plants (WCVP), Royal Botanic Gardens, Kew — https://sftp.kew.org/pub/data-repositories/WCVP/wcvp.zip