TUBEROSE Polianthes tuberosa

Rakthaworn et al. (2009) compared extraction methods on the flowers of the double-flower variety of tuberose, which they name “Polianthes tuberosa L.”. Najar et al. (2024) hydrodistilled fresh flowers of Polianthes tuberosa L. and analysed the essential oil, the hydrosol and the spontaneous emissions of fresh flowers. The first study obtains absolutes, the second an essential oil, a hydrosol and flower emissions: the figures below are given study by study, product by product, and are not combined.

What did Rakthaworn et al. (2009) set out to compare?

The authors state that the objective was to compare “essential oil” extraction methods from the double-flower variety of tuberose. “Essential oil” is the authors’ word: the products the study obtains are absolutes, from enfleurage and from solvent extraction. Tuberose panicles were cut and placed in a water tank to keep the flowers fresh; freshly opened flowers were collected every day, weighed and subjected to extraction. The source does not state the geographic origin, the harvest date or the place of cultivation of these flowers.

How were the tuberose enfleurage absolutes obtained?

In cold enfleurage, the fat — written “palm wax”, then “palm oil” in the same passage of the methods, and “palm stearin (cold enfleurage)” in the results — was heated to 80 °C for 2 h and poured into rectangular glass trays, at 100 ml per tray. The source keeps these three names side by side, and none of them is preferred here. Once the fat had cooled and set at room temperature, flowers were laid on the wax in each tray and covered with another waxed tray; they were replaced with fresh flowers every 24 h. Six pairs of trays were studied, carrying 1,000, 1,500, 2,000, 2,500, 3,000 and 3,500 g of flowers. Table 1 gives the same six masses for treatments 1 to 6 of cold enfleurage, with 200 ml of wax per treatment. The floral scents held in the wax (the “pomade”) were extracted with ethanol, and the ethanol was evaporated, leaving what the authors call the “absolute de enfleurage”. The authors place the saturation point of the “palm stearin” for the absorption of the essential oil of the flowers at 2,500 g of flowers per 200 ml of palm wax, and write that the yield varied from treatment to treatment (figure 1).

In hot enfleurage, flowers were put into 400 ml of “palm oil” warmed to 60 °C for 30 min, then cooled to room temperature; after a night at about 8-10 °C, the palm oil was warmed to 60 °C again. The flowers were then filtered out and replaced with new flowers, the steps being repeated with 300, 400, 500, 600, 700 and 800 g of flowers per treatment. Table 1 gives these masses for treatments 1 to 6 of hot enfleurage, with 400 ml of oil per treatment. For hot enfleurage, they place the saturation point of the palm oil at 500 g of flowers per 400 ml of palm oil, the yield again varying from treatment to treatment (figure 1).

How were the tuberose solvent absolutes obtained?

Six masses of flowers, 100, 150, 200, 250, 300 and 350 g, were soaked in 1 L of each solvent for 1 h; after the debris was removed, the solvents were evaporated, leaving the concrete, from which the absolute was extracted with alcohol. The source writes this protocol once for its two solvents, hexane and petroleum ether. Table 2 gives these masses for treatments 1 to 6 of hexane extraction. For hexane, the authors call 150 g of flowers per litre the “optimum” amount, which gave a yield of 0.0279% (a percentage whose basis the source does not state). Table 2 gives the same masses for treatments 1 to 6 of petroleum ether extraction.

What did the absolutes look and smell like, according to the authors?

The authors describe the absolutes of cold and hot enfleurage as similar in appearance, sticky, waxy orange-brown oils, the cold-process absolute being lighter in colour than the hot-process one; the method of observation is not described. In their assessment, the scent of the cold enfleurage absolute was closer to that of a fresh tuberose flower than the hot enfleurage absolute. The concretes and absolutes obtained with hexane and with petroleum ether looked similar: the concretes were a yellow solid with a tuberose odour, the absolutes brownish yellow with a strong tuberose scent. According to the authors, the scent of the absolute extracted with petroleum ether was closer to that of natural flowers than the absolute extracted with hexane.

What values do the yield figures of the study carry?

In figure 1a (cold enfleurage), treatment 4, 2500 g of flowers per 200 ml of wax, carries the value 0.3137 on an axis labelled “Percentage Yields”; the source states neither the basis of this percentage nor the number of replicates. In figure 1b (hot enfleurage), treatment 3, 500 g of flowers per 400 ml of oil, carries the value 6.5808 on the same “Percentage Yields” axis, with the same basis and replicates left unstated. In figure 2a (hexane extraction), the absolute bar of treatment 2, 150 g of flowers per 1,000 ml of solvent, carries the value 0.0279 on the “Percentage Yields” axis, basis and replicates unstated. The yield of the petroleum ether absolute is given in two different ways by the source and is not reported here.

Which compounds did GC-MS list in the tuberose absolutes?

The authors state that the “Absolutes in petroleum ether and in hexane 100 ppm” (their wording) were analysed for their main chemical components on a Shimadzu QP5050A gas chromatograph–mass spectrometer. That wording is quoted as written, and this page does not attach “100 ppm” to any one of the tables. The source gives neither the column, nor the temperature programme, nor the mode of identification; its tables give each value as a “% Relative peak area” of the sample analysed and each name as one of the “Possible compounds”, so the identifications remain tentative.

Table 3, for the cold enfleurage absolute (the treatment analysed is not stated), lists ten peaks: methyl benzoate (10.996 min, 30.17), methyl salicylate (12.896 min, 12.11), indole (14.567 min, 1.78), (E)-citral (14.818 min, 1.47), methyl anthranilate (15.297 min, 4.45), methyl eugenol (16.021 min, 1.80), (E)-methyl isoeugenol (17.306 min, 8.83), 7-decen-5-olide (17.373 min, 13.33), (z)-beta-farnesene (20.755 min, 2.43) and benzyl benzoate (21.943 min, 23.64).

Table 4, for the hot enfleurage absolute (the treatment analysed is not stated), lists ten peaks: methyl benzoate (10.987 min, 44.85), methyl salicylate (12.904 min, 7.18), 2,4-decadien-1-al (14.740 min, 2.91), (Z)-3-hexenyl 2-oxopropanoate (14.815 min, 27.38), 1-tetradecene (15.736 min, 4.15), (E)-methyl isoeugenol (17.300 min, 1.78), (Z)-nerolidol (17.374 min, 3.35), 1-hexadecene (18.460 min, 3.39), benzyl benzoate (21.922 min, 3.75) and 2-heptadecanone (23.119 min, 1.26).

Table 5, for the absolute obtained by hexane extraction (the treatment analysed is not stated), lists fourteen peaks, with names written as the table writes them: (Z)-3-hexenyl 2-oxopropanoate (14.804 min, 3.70), methyl eugenol (16.009 min, 1.07), methyl isoeugenol (16.744 min, 2.32), (E)-methyl isoeugenol (17.294 min, 1.89), 7-decen-5-olide (17.364 min, 14.96), 2,4,-di-tert-butylphenol (17.494 min, 8.36), 1-hexadecene (18.449 min, 8.85), alpha-farnesol (20.736 min, 1.94), benzyl benzoate (21.901 min, 24.25), benzyl salicylate (24.198 min, 1.39), ecosanol (26.245 min, 4.96), tricosane (32.440 min, 2.47), pentacosane (36.972 min, 19.23) and heptacosane (43.542 min, 4.60).

Table 6, for the absolute obtained by petroleum ether extraction (the treatment analysed is not stated), lists fourteen peaks: methyl anthranilate (15.297 min, 4.15), 1-tetradecene (15.741 min, 0.98), methyl eugenol (16.022 min, 1.89), methyl isoeugenol (16.757 min, 4.85), (Z)-methyl isoeugenol (17.117 min, 0.96), (E)-methyl isoeugenol (17.311 min, 6.05), 7-decen-5-olide (17.385 min, 18.13), 1-hexadecene (18.463 min, 1.69), alpha-farnesol (20.754 min, 4.06), benzyl benzoate (21.935 min, 10.28), benzyl salicylate (24.217 min, 1.34), tricosane (32.462 min, 3.65), pentacosane (37.013 min, 29.44) and heptacosane (43.597 min, 12.53).

Comparing the two solvent absolutes, the authors write that methyl anthranilate, 1-tetradecene and (Z)-methyl isoeugenol were “detected only” in the petroleum ether absolute, and (Z)-3-hexenyl 2-oxopropanoate, 2,4,-di-tert-butylphenol and ecosanol only in the hexane absolute. That statement holds for those two analyses only: the cold enfleurage table carries methyl anthranilate, and the hot enfleurage table carries 1-tetradecene and (Z)-3-hexenyl 2-oxopropanoate.

How did Najar et al. (2024) obtain the essential oil, the hydrosol and the flower emissions?

The plants studied, Polianthes tuberosa L. among them, were provided by the CREA Research Centre for Vegetable and Ornamental Crops (Sanremo, Imperia, Italy) and by the Chambre d’Agriculture des Alpes-Maritimes (CREAM, Nice, France); the article does not say which of the two supplied which species. Full-opened, flawless flowers were collected at the Department of Pharmacy (University of Pisa) and analysed. Extraction was carried out on 20 g of fresh flowers by a 2 h hydrodistillation in a micro-Clevenger-type apparatus; the source gives no oil yield. These methods are common to all the species of the article. During hydrodistillation, 1 mL of HPLC-grade n-hexane was added to the separator funnel, a precaution the authors explain by concerns about the possibility of an essential oil yield as low as one drop — a concern they state, not a measurement. The oil dissolved in hexane and the hydrosol were separated by density difference, and the dissolved oil was analysed directly by GC-MS. The hydrosol was stored in sealed vials at 4 °C in the dark. For the HS-SPME procedure, which covered the spontaneous emissions of fresh flowers (VOC-Fs) and the hydrosols (VOC-Hyd), 1 g of fresh flower or 1 mL of hydrosol was placed in a 50 mL glass vial sealed with aluminium foil and kept at room temperature, and a DVB/CAR/PDMS SPME fibre was exposed to the headspace for 30 min. The fibre was then introduced into the GC-MS injector at 220 °C for 3 min for thermal desorption, and all analyses were performed in triplicate (n = 3).

How were the compounds analysed and identified?

The emissions, the essential oils and the hydrosols were analysed on an Agilent 7890B gas chromatograph fitted with an Agilent HP-5MS capillary column (30 m × 0.25 mm). The carrier gas was helium at 1 mL/min with a column head pressure of 13 psi; the injector was at 220 °C with a split ratio of 1:25, and the oven was programmed from 60 to 240 °C at 3 °C/min. Detection was in full scan, on an Agilent 5977B single quadrupole mass selective detector, with electron impact at 70 eV and a mass acquisition range of 30–300 m/z. Identification was based on comparing retention times with those of authentic samples and on the calculated Kovats Index (van Den Dool and Kratz equation) against a series of C8–C22 n-hydrocarbons; each sample was analysed in triplicate. The section describes this approach without stating, compound by compound, which identification rests on an authentic sample. It does not describe how the percentages are calculated: only the table header, “Relative Abundance (%)”, names them. The table writes its values with a “±” that the source does not define; it is kept as written.

What does the table give for the tuberose essential oil?

In the “EOs” column, the table counts 5 identified compounds.

• “methyl benzoate”: 7.3 ± 0.20 %.
• The table carries a separate row, “methyl ester benzoic acid (=clorius = niobe oil = methyl benzoate)”, with no value in the “EOs” column; the two rows are never added together.
• “precocene ii”: 4.0 ± 0.00 %; the text of the article writes “precocene II”, with the same value.
• “xanthorrhizol”: 2.9 ± 0.10 %; on this row the “VOC-Fs” cell is empty and the “VOC-Hyd” cell carries “-”.
• The table gives xanthorrhizol the class “OS”, but its block of classes has no line for that class: the value is added to no class and to no total.
• “methyl icosanoate (=methyl arachidate)”: 24.4 ± 0.83 %.
• “methyl heneicosanoate”: 58.4 ± 0.65 %; on this row the “VOC-Fs” cell is empty.

In the block of classes for the same column:

• “Esters (ESTs)”: 90.1 ± 1.20 %; the text writes “EO composition (90.1%)”, the same value.
• “Chromene Compounds (CHRs)”: 4.0 ± 0.00 %; the text writes “contributing only 4.0%”, the same value.
• “Phenylpropanoids (PPs)”: the cell carries “0,0”, written with a comma, where the other cells without a value carry “-”.
• The “Non-terpenes” line carries 94.1 ± 0.78 %; the source does not say which classes it groups, and xanthorrhizol is not attached to it here.

What does the table give for the spontaneous emissions of fresh tuberose flowers?

In the “VOC-Fs” column, the table counts 9 identified compounds.

• “eucalyptol”: 1.6 ± 0.33 %.
• The row the table names “methyl ester benzoic acid (=clorius = niobe oil = methyl benzoate)”: 57.3 ± 3.20 %.
• For the same value, the text of the article writes “Methyl benzoate”; each name stays where the source writes it, neither corrects the other, and the table carries a different row named “methyl benzoate”.
• “methyl salicylate”: 13.0 ± 2.57 %.
• “methyleugenol”: 0.6 ± 0.02 %.
• “methyl ether iso-eugenyl”: 5.9 ± 0.21 %; a neighbouring row, named “methyl ether iso-eugenol”, carries a value in the hydrosol column, and the two rows are kept apart.
• “δ-decalactone”: 0.6 ± 0.05 %.
• “jasminelactone”: 13.8 ± 1.80 %; the table’s literature retention index cell for this row is empty.
• “benzyl benzoate”: 5.5 ± 0.56 %.
• “1-hexadecanol”: 0.7 ± 0.06 %.

In the block of classes for the same column:

• “Oxygenated Monoterpenes (OMs)”: 1.6 ± 0.33 %; the hydrosol value of this class is given in two ways by the source and is not reported here.
• “Phenylpropanoids (PPs)”: 6.5 ± 0.10 %.
• “Alcohols (ALCs)”: 0.7 ± 0.06 %.
• “Lactones Compounds (LACs)”: 14.4 ± 1.70 %; the text writes “lactones (14.4%)”, the same value.

What does the table give for the tuberose hydrosol?

In the “VOC-Hyd” column, the table counts 22 identified compounds.

• “2,4,5-trimethyl oxazole”: 7.4 ±0.51 %.
• “4-heptanone”: 0.6 ±0.01 %.
• “methoxy-phenyl oxime”: 15.5 ± 0.91 %; the text writes “oxime, methoxy-phenyl”, the same value.
• “α-pinene”: 0.8 ± 0.04 %.
• “benzaldehyde”: 0.5 ± 0.07 %.
• “β-pinene”: 0.8 ± 0.04 %.
• “6-methyl- 5-hepten-2-one” (spacing as written): 4.5 ± 0.06 %.
• “p-cymene”: 8.9 ± 0.05 %.
• “limonene”: 5.7 ± 0.54 %.
• “eucalyptol”: 38.1 ± 0.3 %.
• “γ-terpinene”: 0.6 ± 0.01 %.
• “1-octanol”: 0.4 ± 0.05 %.
• “nonanal”: 2.8 ± 0.06 %; its class is written “AD” on this row, “ADH” on the other aldehydes.
• “menthone”: 0.2 ± 0.14 %.
• “α-terpineol”: 1.2 ± 0.07 %.
• “estragol”: 0.8 ± 0.02 %.
• “decanal”: 2.4 ± 0.06 %.
• “(E)-anethole”: 0.2 ± 0.13 %.
• “methyleugenol”: 0.8 ± 0.00 %.
• “geranylacetone”: 0.2 ± 0.03 %.
• “methyl ether iso-eugenol”: 2.2 ± 0.09 %; this row stays distinct from the “methyl ether iso-eugenyl” row of the emissions.

In the block of classes for the same column:

• “Monoterpene Hydrocarbons (MHs)”: 16.8 ± 0.2 %; the text writes “MH (16.8%)”, the same value.
• “Apocarotenoids (ACs)”: 0.2 ± 0.03 %.
• “Phenylpropanoids (PPs)”: 3.2 ± 0.30 %.
• “Aldehydes (ADHs)”: 5.7 ± 0.06 %.
• “Ketones (KETs)”: 5.1 ± 0.03 %.
• “Nitrogenous Compounds (NCs)”: 22.9 ± 0.70 %; the text writes “NCs accounted for 22.9%”, the same value.
• “Alcohols (ALCs)”: 0.4 ± 0.05 %.

References

• Govaerts R. (ed.), World Checklist of Vascular Plants (WCVP), Royal Botanic Gardens, Kew — https://sftp.kew.org/pub/data-repositories/WCVP/wcvp.zip
• Rakthaworn P., Dilokkunanant U., Sukkatta U., Vajrodaya S., Haruethaitanasan V. et al., « Extraction Methods for Tuberose Oil and Their Chemical Components », Kasetsart Journal (Natural Science) 2009;43(5):204-211 — https://li01.tci-thaijo.org/index.php/anres/article/download/244817/167283
• Najar B., Pieracci Y., Fratini F., Pistelli L., Turchi B., Varriale D., Pistelli L., Bozzini M.F., Marchioni I., « Exploring the Volatile Composition and Antibacterial Activity of Edible Flower Hydrosols with Insights into Their Spontaneous Emissions and Essential Oil Chemistry », Plants 2024;13(8):1145, doi:10.3390/plants13081145 — https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11053853/fullTextXML