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PhytoChemia Acta

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Oil profiles: dill

17 May 2018

Sarah-Eve Tremblay, M. Sc. A., chimiste

This week, we would like to talk about a very aromatic plant with a characteristic smell: dill (Anethum graveolens). This fragrant plant resembles the fennel (Foeniculum vulgare), and both plants present a strong scent. The two species are part of the Apiaceae family. Dill can reach a height of 1.5 meters and it has the characteristic of re-sowing itself.

Dill is mainly grown for its seeds and weed. Fresh or dried leaves are used to flavor dishes such as salads, fish, sauces and condiments – and, of course, pickles. The seeds are used to flavor drinks and jams. Dill is also known as a stimulant of the digestive system [1].

What interest us more particularly is its essential oils, which are obtained from either the weed or the seeds. It is therefore possible to distinguish the two types of oils by referring to the percentage of the different compounds such as α-phellandrene and limonene which are monoterpenes, dill ether, a characteristic monoterpenic ether, and carvone which is a monoterpene ketone.

Figure 1. Structures of two characteristic constituents of dill oil. (D)-carvone is found in spearmint, and does not feature the same odor as (S)-carvone.

Dill essential oil obtained using the seeds contains a lower percentage of α-phellandrene and dill ether than that obtained by the weeds. Conversely, the oil obtained from the seeds contains a higher percentage of limonene and carvone than that obtained from the weeds. Table 1 summarizes typical percentage ranges for both types of essential oils of dill.

Table #1: Percentages of different compounds for dill essential oil obtained from seeds and weeds

 

Weeds

Seeds

Compounds

%

%

α-Phellandrene

10 to 35%

0.2 to 5.5%

Dill ether

4.5 to 10%

<1%

Limonene

10 to 35%

35 to 50%

Carvone

25 to 40%

42 to 55%

It is therefore possible to relatively easily differentiate whether the essential oil comes from the weeds or seeds when we refer to the percentages of different compounds presented.

The carvone of dill ((S)-carvone) is not the same enantiomer as that present in spearmint (Mentha spicata, which rather features (D)-carvone), and both forms have a different smell [2].

[1] Gurinder, J-K., Daljit, S-A. (2009) Antibacterial and phytochemical screening af Anethum graveolens, Foeniculum vulgare and Trachyspermum ammi, BMC Completementary and Alternative Medecine 2009 9:30.

[2] Leitereg, T. J., Guadagni, D. G., Harris, J., Mon, T. R., Teranishi, R. (1971) Chemical and sensory data supporting the difference between the odors of the enantiomeric carvones, Journal of Agricultural and Food Chemistry, 19(4), 785-787.

Credit Photo: (1) By Tepeyac – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4413610

(2) By H. Zell – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9033257

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