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Mazza, G., F.A. Kiehn, and H.H. Marshall. 1993. Monarda: A source of geraniol, linalool, thymol and carvacrol-rich essential oils. p. 628-631. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.

Monarda: A Source of Geraniol, Linalool, Thymol and Carvacrol-rich Essential Oils

G. Mazza, F.A. Kiehn, and H.H. Marshall

  1. METHODOLOGY
  2. RESULTS AND DISCUSSION
  3. REFERENCES
  4. Table 1
  5. Table 2
  6. Fig. 1
  7. Fig. 2
Monarda, commonly known as horsemint, bee balm, or wild bergamot, belongs to the mint family, Lamiaceae (Labiatae). It is an erect aromatic annual or perennial herb widely distributed throughout North America (Bailey 1977). Several of the 17 to 18 species of this genus have been utilized as ornamental plants, food and flavoring additives, and for medicinal purposes. The essential oil components of the leaves have been used to determine genetic relationships between species (Scora 1967). Plants of a given species from different geographical regions may, however, yield strikingly different oils.

Monarda fistulosa L., native to the Canadian prairies, is drought tolerant, winter hardy, and may yield an essential oil high in geraniol content (Marshall and Scora 1972; Mazza et al. 1987). When this native species is crossed with M. didyma, vigorous hybrids, yielding essential oils rich in geraniol, linalool, thymol, carvacrol, 1,8-cineole, and other terpenes can be produced. In the present study, the content and composition of the nitrogen extracted volatiles and hydrodistillated oils from eight winter-hardy, powdery mildew, and rust-resistant hybrids were determined, with the aim of developing new alternative crops for Canadian agriculture.

METHODOLOGY

A plantation of over 500 hybrids and clones of M. fistulosa var. menthaefolia and M. didyma 'Cambridge Scarlet', planted at approximately 10,000 plants/ha was established at Agriculture Canada Research Station, Morden, Manitoba, Canada in 1981. Plants were allowed to establish and grow under dryland culture, as described previously (Marshall and Chubey 1983). In 1987, all surviving plants (about 20% of the original number of plants) were analyzed for volatile constituents and eight of these clones were selected for possible commercial exploitation. These eight clones were propagated by softwood stem cuttings taken at the end of May, and field planted the end of June, 1988. In 1989 and 1990, 10 to 20 plants from each clone were harvested between July 5 and July 10, when the plants were in full bloom. After harvest, the whole plants (stems, leaves, and flowers) were cut into 2 cm lengths, weighed for yield determination and stored separately at -20°C in sealed plastic bags until used.

The essential oil was extracted by hydrodistillation of the plant material using 600 g in a 5 liter round-bottomed flask with distilled, deionized water (2,400 ml), and a receiver for oils lighter than water. The distillation period was 2 h, and the essential oil content was determined on an oil weight to dry tissue weight basis. Headspace volatiles of the chopped plant material were extracted and concentrated by passing a stream of purified nitrogen (80 ml/min for 15 h; 21±1°C) over the samples. The volatiles were adsorbed onto Tenax GC traps prepared by packing 100±2 mg of 60-80 mesh Tenax GC into a 65 mm i.d. x 12 cm Pyrex tubing between pesticide grade silanized glass wool plugs. Monarda volatiles were subsequently eluted from the Tenax GC traps with 1 ml of freshly redistilled diethyl ether. Essential oil and headspace samples were analyzed using a Varian Model 3400 gas chromatograph equipped with a flame ionization detector (FID). A 30 m x 0.25 mm i.d. fused silica capillary column packed with 1 µm J&W DB-5 [polymethyl(5% phenyl) siloxane] was used for the separation of volatiles. The operating conditions were: injection port temperature, 230°C; detector temperature 250°C; column temperature programmed at 60°C for 0 min, 60deg. to 104°C at 4°C/min, 104° to 182°C at 6°C/min and at 182°C for 6 min; carrier gas flow rate, 1 ml He/min; linear velocity 24 cm/s.

Identification of the compounds was made by combined gas chromatography mass spectrometry (GC/MS) and by comparing retention times of monarda components with those of authentic compounds. A Finnigan MAT 90 mass spectrometer coupled with a Varian Model 3400 gas chromatograph was used for GC/MS analyses.

RESULTS AND DISCUSSION

The composition of the oils obtained by hydrodistillation of the plant material varied significantly among different hybrids (Fig. 1, Table 1). Six cyclic terpenes, including alpha-phellandrene, alpha-pinene, and camphene were present in oils of seven of the eight hybrids and ß-pinene ranged from 0.56 to 13.8% of the oil from these hybrids. The oil from the 'Morden #3' hybrid had practically no cyclic terpenes; however, analysis of the headspace of this hybrid revealed significant levels of these compounds (Table 2). Geraniol accounted for well over 90% of the composition of the oil from the hybrid, 'Morden #3'. Other components found in this oil at 0.5% level or higher included linalool, ß-myrcene, linalyl acetate, and a sesquiterpene, tentatively identified as germacrene-D. Presently, the chief natural source for geraniol is citronella oil, wherein it occurs with citronellal and citronellol and from which it is separated by fraction distillation (Kirk-Othmer 1983). The geraniol-rich 'Morden #3' originated from a cross between a geraniol race of M. fistulosa var. menthaefolia native to southern Manitoba, and the progeny of colchicine treated selection 65-5 (Fig. 2). 'Morden #3' was recommended for use as a commercial and competitive source of geraniol earlier (Marshall and Chubey 1983; Mazza et al. 1987), and over 70 ha are presently grown in southern Alberta for geraniol production. Geraniol is used in perfumery for its rosy scent, and in food products as a flavor ingredient. The essential oil of selection 75-1A contained over 73% carvacrol, while selection 75-1B oil contained 31% thymol (Table 1).

Linalool represented 45.7% of selection 80-1A, 49.8% of `Marshall's Delight', and 67.0% of selection L87-1 essential oil (Table 1). This substantiates the close relationship existing between these three selections (Fig. 2); however, the other closely related selection, 80-1B, had only 0.4% of linalool, and a high amount of carvacrol (22.3%), 1,8-cineole (22.2%), ß-pinene (13.8%), and ocimene (6.2%). Therefore, a definite genetic segregation appears to have occured.

The oxygenated terpene, 1,8-cineole, occurred in all samples and represented 4.8, 14.1, and 22.2% of the oils from 'Marshall's Delight', '75-1B', and '80-1B' Monarda, respectively. 1,8-Cineole, also known as eucalyptol, cajuputoal, 1,8-oxido-p-menthane, or 1,8-epoxy-p-menthane, occurs in numerous essential oils (about 270) and is used widely in pharmaceutical preparations and food products such as beverages, ice cream, candies, baked goods, and chewing gum.

Propagation of these selections of monarda can easily be achieved through crown divisions, but this method is cumbersome and inefficient. A more effective and rapid method of propagation has been found to be through plant cuttings of actively growing stems. Stem cuttings, approximately 10 to 12 cm in length, are taken and all but two leaves removed, including the shoot tip. The bases of the cuttings are dipped in 1,000 ppm IBA rooting compound and placed in sand in a misting chamber. Cuttings taken in early June when the plants are actively growing produce root initials within one week and are ready for transplanting within 14 to 16 days. Propagation by tissue culture has also been successfully carried out in our laboratory using leaf cuttings.

Weeds do not pose a problem in the production of monarda. Herbicides such as trifluralin, terbacil, solan, and paraquat used together with good cultural practices can maintain a weed-free plantation. Trifluralin (1.12 kg/ha) should be used pre-plant incorporated when monarda is established. In the second year and every year thereafter, paraquat can be applied before the monarda shoots reach a height of 5 cm, to kill the early spring weeds. Application of herbicides in a commercial field, however, should only be used if the chemicals are legally registered for such use on this crop. This also kills off the monarda shoots. Application of terbacil (1.68 kg/ha) and 1 to 2 cm of irrigation should follow.

Rust, Puccinia mentha, is the major disease of Monarda. It has caused defoliation, girdling of stems, and degeneration of plants. The disease is spread by aerial rust spores under cool, cloudy, moist weather conditions. Relatively good control has been achieved by applying a contact herbicide, paraquat, in early spring when the monarda shoots are only about 5 cm tall to destroy all vegetation and thereby remove the required host for the spores.

Essential oil yield varies from about 0.65 to 1.2 g/100 g of fresh plant material (Table 1), or depending on the hybrid, 60 to 125 kg of oil/ha. As a result, it is our believe that four of these hybrids of monarda may have the potential of becoming commercial sources of geraniol, linalool, tymol, and carvacrol.

REFERENCES

Table 1. Chemical composition of essential oils of Monarda selectionsz.

Relative composition (% of total oil)
Peaky Constituent Morden #3 Marshalls Delight 75-1A 75-1B 84-2 80-1B 80-1A L87-1
1 a-Thujene tr 0.7 2.1 1.4 2.3 1.1 0.8 0.6
2 a-Pinene ---x 0.6 0.6 1.7 0.6 2.4 0.3 0.3
3 Camphene --- 0.3 0.1 1.2 0.1 1.5 0.2 0.2
4 ß-Pinene 0.3 7.6 0.6 8.7 1.4 13.8 1.7 0.8
5 1-Hepten-3-ol tr 0.7 0.1 1.6 0.3 2.3 0.1 0.3
6 ß-Myrcene 1.4 1.6 2.4 2.5 2.5 2.7 1.2 0.9
7 a-Phellondrene tr 0.1 0.4 0.2 0.4 0.2 0.1 0.1
8 a-Terpenene tr 0.9 2.2 2.1 3.9 1.3 1.2 0.5
9 p-Cymene/Limonene tr 1.3 6.0 3.0 4.2 1.7 2.5 0.6
10 1,8-Cineole 0.1 4.8 1.0 14.1 1.0 22.2 0.5 0.4
11 Unknown (C12H20O2) 0.3 0.1 0.1 1.0 0.1 0.9 0.1 0.1
12 Ocimene 0.7 5.9 8.1 5.9 27.1 6.2 6.9 2.3
13 Bornyl acetate tr 0.5 0.1 1.2 0.1 1.7 0.1 0.1
14 Linalool 1.1 49.8 0.1 1.5 0.3 0.4 45.7 67.0
15 Borneol tr 0.3 tr 2.0 tr 2.0 0.2 0.3
16 Terpinen-4-ol tr 0.7 0.8 1.0 0.5 1.1 0.5 0.3
17 a-Terpineol tr 3.4 0.1 7.8 0.1 12.0 0.1 0.1
18 C10H12O2 0.6 tr --- 5.4 0.1 tr --- ---
19 Neroly 0.4 --- --- tr 3.3 0.1 --- tr
20 Geraniol 92.6 1.5 0.1 tr --- --- 0.1 tr
21 Neral 0.2 --- --- --- --- --- tr ---
22 Thymol tr 0.5 0.3 31.1 0.1 3.1 1.4 0.4
23 Carvacrol tr 17.8 73.5 3.8 49.6 22.3 33.3 22.4
24 Geranial 0.4 0.4 0.1 0.4 0.4 0.5 0.3 0.2
25 Jasmone 0.1 0.1 0.1 0.1 0.1 0.1 0.1 tr
26 ß-Caryophellene 0.2 0.4 0.1 0.4 0.4 0.5 0.3 0.2
27 Germacrene-D 0.8 1.0 0.5 0.5 0.7 0.7 1.3 0.8
Yield of oil (g/100 f.wt.) 1.2 0.6 1.1 0.6 1.1 0.7 0.8 1.0
zIdentification for compounds 1, 4, 7, 13, 17, 18, 21, 25, 26, and 27 based on GC-MS data only.
yRefers to peak number in Fig. 1. Listed in order of elution.
xnot detected.

Table 2. Volatile composition of the essential oil of geraniol-rich 'Morden #3' monardaz.

Relative composition
(% of total essential oil)
Peaky Essential oil constituent Oil Headspace
1 alpha-Thujene tr 1.3
2 alpha-Pinene ---x 0.5
3 Camphene --- 0.1
4 ß-Pinene 0.3 6.0
5 1-Hepten-3-ol tr 1.1
6 Myrcene 1.4 14.6
7 alpha-Phellandrene tr 0.2
8 alpha-Terpenene tr 7.2
9 p-Cymene/Limonene tr 0.4
10 1,8-Cineole 0.1 0.2
11 Unknown (C12H20O2) 0.2 1.1
12 Ocimene 0.7 8.6
13 Bornyl acetate tr tr
14 Linalool 1.1 3.0
15 Borneol tr 0.1
16 Terpinen-4-ol tr 0.3
17 alpha-Terpineol tr 0.2
18 C10H12O2 0.6 1.2
19 Nerol 0.4 3.5
20 Geraniol 92.6 39.5
21 Neral 0.2 3.6
22 Thymol tr tr
23 Carvacrol tr tr
24 Geranial 0.4 0.5
25 Jasmone 0.1 0.3
26 ß-Caryophellene 0.2 0.7
27 Germacrene-D 0.8 2.5
zIdentification for compounds 1, 4, 7, 13, 17, 18, 21, 25, 26, and 27 based on GC-MS data only.
yRefers to peak number in Fig. 1. Listed in order of elution.
xNot detected.



Fig. 1. Chromatograms of essential oils from four Monarda selections. For peak designation see Table 1.

Fig. 2. Pedigree of Monarda selections.
Last update September 18, 1997 aw