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.
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 (R)-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
Here in Germany, the typical Sauerkraut (https://en.wikipedia.org/wiki/Sauerkraut) is often flavored with caraway seeds, but they are also replaced by dill seeds as they have a similar (S)-carvone flavor (maybe a little softer, rounder).
There is a nice work form 1985 regarding the typical scent of fresh Anethum graveolens herb: Main aroma compounds of fresh dill were α-phellandrene (1980mg/kg), dill ether (398mg/kg), β-phellandrene (275mg/kg), and limonene (100mg/kg). Air-drying and freeze-drying led to severe losses of all aroma compounds, especially of α-phellandrene and dill ether. Aroma content of freeze-dried dill was lower than 10% than of fresh herb, but about four-fold that of dried dill. „So freeze-drying is superior to air-drying in dill processing.“
[Huopalahti, R., & Kesälahti, E. (1985). Effect of Drying and Freeze-Drying on the Aroma of Dill – Anethum Graveolens CV Mammut. In Essential Oils and Aromatic Plants (pp. 179-184). Springer Netherlands.]
(S)-α-Phellandrene is a typical example of so many important aroma compounds lost by processing (drying, distillation). In 1992, Imre Blank wrote: „The dependence of the characteristic odour note of dill herb on the concentration levels of five compounds, having the highest odour units in an extract obtained from the fresh material, was studied. (S)-α-Phellandrene was evaluated as the character-impact compound of the dill flavour which was rounded off by an additive effect of (3R,4S,8S)-3,9-epoxy-1-menthene (dill ether). The contributions of myristicin, methyl 2-methylbutanoate and (R)-limonene to the dill flavour appeared less significant.“
[Sensory study on the character-impact flavour compounds of dill herb (Anethum graveolens L.). Imre Blank, Alina Sen, Werner Grosch, Food Chemistry, Volume 43, Issue 5, 1992, Pages 337-343] http://www.imreblank.ch/FC_1992_43_337.pdf
Very interesting studies. Thank you for sharing!