CHEMICAL EXTRACTION

What is solvent extraction?

According to the review by Cravotto et al. (2022), two extraction processes are commonly used in industry to extract aromatic compounds from plants, hydrodistillation and solvent extraction: the first gives an essential oil, the second a crude extract called concrete. In their conclusion, Erbaş and Baydar (2016) write that, for the perfume industry, concrete and absolute are produced by solvent extraction at low temperatures. According to the same authors, volatile oil compounds are generally non-polar molecules, so they can be largely extracted by dissolving them in a non-polar solvent, the most common one in these extractions being n-hexane.

What are concretes, absolutes and resinoids?

Canton et al. (2025, §1 Introduction) call galbanum the resinoid obtained by non-polar solvent extraction of the gum resin collected by incision from the lower part of the stem of Ferula gummosa Boiss. (Ferula galbaniflua Boiss. in the study).

How does a concrete become an absolute?

Ray et al. (2014) describe the use of a non-polar solvent such as hexane to “wash” the aromatic compounds out of the flowers; once the hexane is evaporated, a waxy, semi-solid substance remains, the concrete. According to the same authors, the concrete then undergoes a series of “washings” with a polar solvent such as ethanol, whose polarity allows the volatile aromatics to be extracted from the concrete while leaving behind the non-polar plant waxes, which do not dissolve in ethanol.

What did individual studies do and measure?

Tobacco flowers (Popova et al., 2020)

In the study by Popova et al. (2020), the concretes of the flowers of Nicotiana rustica L., Nicotiana glutinosa L., Nicotiana alata Link & Otto and Nicotiana tabacum L. were obtained by twofold extraction with n-hexane, in batch mode, for 60 and 30 min at 30 °C, with a raw material-to-solvent ratio of 1:10. The extracts were then concentrated on a rotary vacuum evaporator with a water bath at 35 °C.

The concrete yields varied between species: 1.4 % (N. rustica), 2.5 % (N. glutinosa), 1.6 % (N. alata, white-flowered genotype), 2.7 % (N. alata, pink-flowered genotype), 3.2 % (N. tabacum, Oriental type) and 5.2 % (N. tabacum, Virginia type).

In their discussion, the authors write that the yield of flower concretes, from 1.42 % to 5.24 %, “could” be considered satisfactory, similar ranges having been observed for other essential-oil-bearing plants.

Lavender absolutes (Nedeltcheva-Antonova et al., 2022)

Nedeltcheva-Antonova et al. (2022) studied samples designated LA1 to LA7. The article names the species “Lavandula angustifolia Mill.” in its title and “L. angustifolia L.” in §2.1. According to the description of the samples, lavender concrete is extracted from fresh, unsteamed flower mass, harvested from the beginning of flowering to mass flowering (40–80 % of inflorescences in bloom), and treated with a non-polar solvent (petroleum ether or n-hexane). This concrete is described as a yellow-green to green-brown jelly-like mass containing over 65 % absolute, and the absolute obtained from it as a yellowish-green, thin, clear liquid with an aroma typical of lavender. Sample LA7, the so-called “Lavera” absolute, a dark green to brown viscous liquid with a grassy lavender scent and a hint of honey, was obtained from a “Lavera” concrete derived from exhausted lavender inflorescences. Linalool accounted for 27.33–38.24 % in samples LA1–LA6 and 20.74 % in LA7. Linalyl acetate ranged from 26.58 to 37.39 % in LA1–LA6 and, in the authors’ word, “surprisingly”, was not observed in LA7.

Jasmine flowers (Yassen et al., 2026)

In the study by Yassen et al. (2026), fresh flowers of four species, Jasminum sambac (L.) Aiton, Jasminum azoricum L., Jasminum grandiflorum L. and Jasminum multiflorum (Burm.f.) Andrews, were harvested early in the morning in August. Following a “previously reported” method, they were extracted three times separately with hexane, 10 g of freshly opened flowers being soaked in 100 mL of hexane and shaken for 1 h. The extracts were filtered and the solvent evaporated under vacuum at a maximum of 40 °C to give the concrete. Following the method of Tamogami et al., the absolute was then extracted from the concrete with 95 % ethanol, washed three times and filtered at -80 °C to remove wax, the alcohol being evaporated at temperatures below 40 °C. In the text of the results, the concrete yields of the four species range from 0.52 to 0.96 % and the absolute yields from 39.67 to 61.3 %. Table 1 gives, for concrete (on flower basis) and absolute (on concrete basis), 0.52 % and 61.28 % for J. sambac, 0.81 % and 47.87 % for J. azoricum, 0.76 % and 39.67 % for J. grandiflorum, and 0.96 % and 45.54 % for J. multiflorum.

Oil-bearing rose (Erbaş and Baydar, 2016)

In the study by Erbaş and Baydar (2016), on rose, Rosa × damascena Herrm. (Rosa damascena Mill. in the study), the flowers were extracted in separating funnels with each of five non-polar solvents, diethyl ether, petroleum ether, cyclohexane, chloroform and n-hexane, in three successive stages of 30, 20 and 15 minutes, a multistage extraction the authors performed to increase the yield.

After evaporation of the solvents on a rotary evaporator under vacuum, the rose concrete was a pale reddish, waxy, semi-solid material.

Following their references 8 and 9, the concretes, treated with about 10 times their own weight of ethanol, were dissolved in 96 % ethanol and stirred vigorously at 35–40 °C for 8 h, then the alcoholic solution was chilled at -20 °C for 8 h and the crystallised stearoptenes filtered under vacuum. The stearoptenes were redissolved in 50 mL of 96 % ethanol, and the filtrate, left overnight in a freezer, was evaporated under vacuum on a rotary evaporator at 55 °C to remove ethanol and water and give the absolute.

What yields does the study report?

Table 2 (p. 561) defines concrete yield as the amount of concrete recovered from 100 kg of fresh flowers (v/w) and absolute yield as the amount of absolute recovered from 100 kg of concrete (v/w). Per solvent, it gives concrete yield, concrete productivity (kg of fresh flowers per kg), absolute yield and absolute productivity: diethyl ether 0.66 % / 150.1 / 60.1 % / 249.7; petroleum ether 0.45 % / 223.5 / 43.8 % / 514.5; cyclohexane 0.43 % / 230.5 / 45.4 % / 520.6; chloroform 0.44 % / 233.6 / 52.1 % / 450.5; n-hexane (control) 0.30 % / 336.2 / 70.9 % / 474.4. In the text of §3 (p. 561), the authors write that concrete yields were between 0.30 % and 0.66 % and absolute yields between 52.1 % and 70.9 %. Table 2, on the same page, lists absolute yields of 43.8 % for petroleum ether and 45.4 % for cyclohexane. According to the same text, the highest concrete yield (0.66 %) and productivity (1 kg from 150.1 kg of fresh flowers) were obtained with diethyl ether, and the highest absolute yield (70.9 %) and productivity (1 kg from 249.7 kg of fresh flowers) by ethyl alcohol extraction of the n-hexane and diethyl ether concretes respectively.

What separates the concrete from the absolute?

Phenylethyl alcohol and nonacosane were the major compounds of all the rose concretes tested. Nonacosane was not detected in the rose absolutes; according to the authors, this compound is “probably” not soluble in ethyl alcohol and remains in the solid residue.

Galbanum resinoid (Canton et al., 2025)

In the first distillation by Canton et al. (2025), 7.02 g of brown viscous liquid (the non-volatile part) remained in the loading flask and 2.97 g of clear yellow liquid (the volatile part) condensed in the recovery flask. The authors put the non-volatile part at 64 % of the starting material and the recovered volatile part at 27 %.

Why is hexane used, and what do authors write about replacing it?

Cravotto et al. (2022) describe hexane as a solvent used extensively in the food industry to extract vegetable oils, fats, flavours, fragrances, colour additives and other bioactive ingredients. According to the same review, among the solvents used industrially to extract non-polar edible natural products such as colours, flavours, fragrances or lipids, hexane is “undoubtedly the most widely used”. The review states that hexane, and in particular the n-hexane isomer, has been shown to be neurotoxic to humans and has been listed as a cause of occupational diseases in several European countries since the 1970s.

At the end of their study on rose, Erbaş and Baydar (2016) write that the alternative to n-hexane that “seemed” most feasible was diethyl ether, on account of its higher concrete yield, absolute productivity and phenylethyl alcohol content. In the same passage, they note that diethyl ether is extremely flammable and “may” be explosive according to the standard operating procedures.

In the original text of Regulation (EC) No 1272/2008 (CLP), Annex VI, Part 3, Table 3.1 (later adaptations of Annex VI not read), entry 601-037-00-0 concerns n-hexane (EC No 203-777-6, CAS No 110-54-3), classified Flam. Liq. 2, Repr. 2, Asp. Tox. 1, STOT RE 2 *, Skin Irrit. 2, STOT SE 3 and Aquatic Chronic 2, with hazard statement codes H225, H361f ***, H304, H373 **, H315, H336 and H411. For labelling, the entry gives the pictogram and signal word codes GHS02, GHS08, GHS07, GHS09 and Dgr, the same hazard statement codes, no supplementary hazard statement code, and the specific concentration limit “STOT RE 2; H373: C ≥ 5 %”.

What does Directive 2009/32/EC set for extraction solvents?

Under Article 1(1) of Directive 2009/32/EC of 23 April 2009, the directive applies to extraction solvents used or intended for use in the production of foodstuffs or food ingredients. Annex I lists the extraction solvents which “may” be used during the processing of raw materials, foodstuffs, food components or food ingredients; its Part I, extraction solvents to be used in compliance with good manufacturing practice “for all uses”, names propane, butane, ethyl acetate, ethanol, carbon dioxide, acetone and nitrous oxide. Note (1) to Part I states that an extraction solvent is considered as being used in compliance with good manufacturing practice if its use results only in the presence of residues or derivatives in technically unavoidable quantities presenting no danger to human health. Part II, extraction solvents for which conditions of use are specified, sets for hexane maximum residue limits in the extracted foodstuff or food ingredient: 1 mg/kg in the fat, oil or cocoa butter (production or fractionation of fats and oils, production of cocoa butter); 10 mg/kg in the food containing the defatted protein products and defatted flours, and 30 mg/kg in defatted soya products as sold to the final consumer (preparation of defatted protein products and defatted flours); 5 mg/kg in defatted cereal germs (preparation of defatted cereal germs). Note (3) of Annex I defines hexane as a commercial product consisting essentially of acyclic saturated hydrocarbons containing six carbon atoms and distilling between 64 °C and 70 °C, and states that the combined use of hexane and ethylmethylketone is forbidden. Part III sets the maximum residue limits in the foodstuff due to the use of extraction solvents in the preparation of flavourings from natural flavouring materials: 2 mg/kg for diethyl ether, 1 mg/kg for hexane and 1 mg/kg for cyclohexane.

References

• Cravotto C., Fabiano-Tixier A.-S., Claux O., Abert-Vian M., Tabasso S. et al., « Towards Substitution of Hexane as Extraction Solvent of Food Products and Ingredients with No Regrets », Foods 2022;11(21):3412, doi:10.3390/foods11213412 — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pmc&id=9655691&rettype=xml
• Erbaş S., Baydar H., « Variation in Scent Compounds of Oil-Bearing Rose (Rosa damascena Mill.) Produced by Headspace Solid Phase Microextraction, Hydrodistillation and Solvent Extraction », Records of Natural Products 2016;10(5):555-565 — https://www.acgpubs.org/uploads/articles/pdfs/2018080807064667-RNP-1412-058.pdf
• Popova V., Ivanova T., Stoyanova A., Nikolova V., Hristeva T. et al., « GC-MS Composition and Olfactory Profile of Concretes from the Flowers of Four Nicotiana Species », Molecules 2020;25(11):2617, doi:10.3390/molecules25112617 — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pmc&id=7321308&rettype=xml
• Canton M., Thierry M., Larras F., Bicherel P., Mata L. et al., « Chemical Profiling of Volatile and Non-Volatile Fractions of Galbanum (Ferula galbaniflua Boiss.) Used in Perfumery », Chemistry & Biodiversity 2025;22(12):e01442, doi:10.1002/cbdv.202501442 — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pmc&id=12715999&rettype=xml
• Nedeltcheva-Antonova D., Gechovska K., Bozhanov S., Antonov L., « Exploring the Chemical Composition of Bulgarian Lavender Absolute (Lavandula angustifolia Mill.) by GC/MS and GC-FID », Plants 2022;11(22):3150, doi:10.3390/plants11223150 — https://www.ebi.ac.uk/europepmc/webservices/rest/PMC9692913/fullTextXML
• Ray H., Majumdar S., Parua Biswas S., Das A., Ghosh T.K. et al., « Characterization of the Volatile Aroma Compounds from the Concrete and Jasmine Flowers Grown in India », Chemical Engineering Transactions 2014;40:265-270, doi:10.3303/CET1440045 — https://www.aidic.it/cet/14/40/045.pdf
• Yassen M.S., Ayoub I.M., El-Ahmady S.H., Singab A.N.B., « Comparative analysis of flower volatiles from four Jasminum species growing in Egypt using multivariate analysis », Scientific Reports 2026;16:8947, doi:10.1038/s41598-026-39688-w — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pmc&id=12988214&rettype=xml
• Directive 2009/32/EC of the European Parliament and of the Council of 23 April 2009 on the approximation of the laws of the Member States on extraction solvents used in the production of foodstuffs and food ingredients (Recast) — https://publications.europa.eu/resource/celex/32009L0032
• Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006 — https://publications.europa.eu/resource/celex/32008R1272
• Govaerts R. (ed.), World Checklist of Vascular Plants (WCVP), Royal Botanic Gardens, Kew — https://sftp.kew.org/pub/data-repositories/WCVP/wcvp.zip