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Simon, J.E., J. Quinn, and R.G. Murray. 1990. Basil: A source of essential oils. p. 484-489. In: J. Janick and J.E. Simon (eds.), Advances in new crops. Timber Press, Portland, OR.

Basil: A Source of Essential Oils*

James E. Simon, James Quinn, and Renee G. Murray

  1. INTRODUCTION
  2. ANALYSIS OF ESSENTIAL OILS
  3. SELECTION
  4. PROSPECTS
  5. REFERENCES
  6. Table 1
  7. Table 2
  8. Table 3
  9. Fig. 1
  10. Fig. 2
  11. Fig. 3

INTRODUCTION

The genus Ocimum, (Lamiaceae formerly Labiatae), collectively called basil has long been recognized as a diverse and rich source of essential oils (Table 1). Ocimum contains between 50 to 150 species of herbs and shrubs from the tropical regions of Asia, Africa, and Central and South America (Bailey 1924, Hortus III 1976, Darrah 1980). Plants have square stems, fragrant opposite leaves, and whorled flowers on spiked inflorescences (Darrah 1980). Interspecific hybridization and polyploidy, common occurrences within the genus, have created taxonomic confusion and challenges, yet very little has been published on basil taxonomy which follows the International Code of Botanical nomenclature (Tucker 1986). The morphological diversity within basil species has been accentuated by centuries of cultivation with great variation in pigmentation, leaf shape and size, and pubescence. Taxonomy is further complicated by the existence of chemotypes or chemical races within the species that do not differ significantly in morphology.

Sweet basil (Ocimum basilicum L.), a common garden herb, is cultivated in the United States for culinary purposes as a fresh herb and as a dried spice (Fig. 1). While there are many cultivars (Simon and Reiss-Bubenheim 1987), little information is available on the essential oil compounds responsible for the plant's flavor and fragrance.

The essential oils of basil extracted via steam distillation from the leaves and flavoring tops are used to flavor foods, dental and oral products, in fragrances, and in traditional rituals and medicines (Guenther 1949, Simon et al. 1984). Extracted essential oils have also been shown to contain biologically-active constituents that are insecticidal (Deshpande and Tipnis 1977, Chavan and Nikam 1982, Chogo and Crank 1981), nematicidal (Chatterjee et al. 1982), fungistatic (Reuveni et al. 1984) or which have antimicrobial properties (Ntezurubanza et al. 1984). These properties can frequently be attributed to predominant essential oil constituents, such as methyl chavicol, eugenol linalool, camphor, and methyl cinnamate. Two minor components of the essential oil of sweet basil, juvocimene I and II, have been reported as potent juvenile hormone analogs (Nishida et al. 1984).

There are several types of basil oil in international commerce, each derived principally from different cultivars or chemotypes of sweet basil. The oils of commerce are known as European French or Sweet Basil, Egyptian, Reunion or Comoro; and to a lesser extent Bulgarian and Java basil oils (Heath 1981). The European type of basil oil considered to be the highest quality, and producing the finest odor, characteristically contains: linalool; methyl chavicol; and to a lesser extent 1,8-cineole, alpha-pinene; ß-pinene; myrcene; ocimene; terpinolene; camphor; terpinen-4-ol; alpha-terpineol; eugenol; and sesquiterpenes (Guenther 1949; Simon et al. 1984). Egyptian basil oil of commerce is similar to European basil oil except that the concentration of d-linalool is significantly lower while the concentration of methyl chavicol is significantly higher (Fleischer 1981). In contrast, Reunion or Comoro basil oil contains little if any d-linalool and is a harsher, spicy oil due to the very high concentration of methyl chavicol, and to a lesser extent, 1,8-cineole, borneol camphor and eugenol (Lawrence et al. 1972 Simon et al. 1984). Bulgarian and Java basil oils are rich in methyl-cinnamate and eugenol respectively (Heath, 1981).

Since 1984, we have been characterizing the chemical diversity of Ocimum spp. to identify chemotypes of potential commercial interest. Genetic and breeding studies have been initiated to increase the total essential oil content (concentration) of commercial basil chemotypes and to increase the content of specific oil constituents in other chemotypes such as those high in methyl chavicol and methyl cinnamate. A germplasm collection of basil (Ocimum spp.) consisting of more than 100 accessions from the USDA Plant Introduction Station which include O. basilicum, O. canum, O. gratissimum, O. kilimandscharicum, O. citriodorium, O. micranthum, O. sanctum plus other commercial and noncommercial seed sources were field grown in central Indiana and were initially screened organolepticahy for aroma and flavor differences. Each accession and cultivar was harvested during full bloom.

ANALYSIS OF ESSENTIAL OILS

More than 60 accessions of Ocimum spp. were selected for analysis based on notable differences in aroma. These plants were then harvested at full bloom and the essential oil extracted immediately from the flowering tops by hydrodistillation using modified Clevenger traps. Analysis of the essential oils was accomplished by gas chromatography using a Varian FID-GC (3700), with a fused silica column (OV101) and integrator (4270) as previously described (Charles and Simon 1990). Compound verification was by GC/Mass spectroscopy using a Finnegan GC (9610) and MS (4000) with a Data General Nova/4 data processing system.

The essential oil content ranged from 0.04 to 0.70% (v/fresh weight) within the Ocimum germplasm collection. Chemotypes high in 1,8-cineole, trans-ß-ocimene, camphor, linalool methyl chavicol geraniol, citral eugenol, methyl cinnamate, methyl eugenol, ß-caryophyllene, and elemene, and ß-bisabolene were identified (Table 2). Accessions varied in essential oil content, and showed diversity in growth, form, flowering and pigmentation (Fig. 2).

The major essential oil constituents found in commercial cultivars of 'Sweet Basil' included linalool and methyl chavicol, followed by eugenol and 1,8-cineole. In the red-leaved ornamental cultivars of sweet basil 'Dark Opal', methyl chavicol was only a minor constituent. Cultivars of basil yielding high percentages of linalool, eugenol, citral (neral and geranial) and ocimene were also identified (Table 3).

SELECTION

Once plants with distinct morphological and/or chemical characteristics are identified in open pollinated crops, rapid progress can be made by mass selection. This is particularly true with plant species such as those of Ocimum, in which little plant breeding and crop improvement has occurred. Such an approach has been used to identify and develop new lines of Ocimum gratissimum L., rich in eugenol (Sobti et al. 1982). In 1987, we initiated a study to develop a high methyl cinnamate basil as this type was of interest to the perfume industry. Four accessions of basil were selected from the screening program on the basis of high methyl cinnamate (MC): Cinnamon Basil (Park Seed), 35% MC; USDA No. 170579,29% MC; Mexican Spice Basil, 17% MC; and a selection from Morocco, 16% MC. The non-selected population consisted of 10 plants randomly selected from each accession in the greenhouse and transplanted into the field. The selected population consisted of 10 plants from each accession selected organoleptically (by scent) for high methyl cinnamate. Field-grown plants were sampled during full bloom for essential oil and methyl cinnamate content and open pollinated seed collected. Organoleptic selection was successful as confirmed by essential oil analysis. The 1987 selected population had 15% more methyl cinnamate than the non-selected population although the total content or concentration of essential oils was essentially the same. In 1988, seed derived populations (1,000 plants of each) were sampled at post full-bloom. Fifty plants from the 1988 selected population were further selected organoleptically for high and low methyl cinnamate and chemical analysis reconfirmed the effectiveness of selection for higher methyl cinnamate.

PROSPECTS

In northern Indiana, field production of basil was initiated on a semi-commercial basis (4 ha) in 1987 and 1988 to identify potential production-related problems, and obtain initial yield information production costs, and essential oil samples for industrial evaluation. The crop appears to be well adapted to Indiana and can be grown and processed like peppermint and spearmint long established essential oil crops in Indiana (Fig. 3). A major field production problem included the lack of effective (and registered) pre- and post-emergent herbicides for seasonal weed control. The presence of weeds, particularly broadleaf species, in the "hay" (the partially field-dried essential oil plant at extraction time), can detrimentally alter the odor of essential oil and reduce the quality of the extracted oil product. The lack of commercially available seed of cultivars (or chemotypes) with specific and acceptable chemical characteristics has been a production limitation. However, selection of unique chemotypes that have market potential could provide a competitive edge for domestic growers.

Another limitation in the commercialization of domestically produced basil essential oils is market penetration and the difficulty in producing basil oils that match chemically and organoleptically with the currently imported basil oils. Our initial studies indicate that basil essential oils produced in Indiana can be price competitive with the imported product. With the correct chemotypes of basil growers could produce standard basil oils and reduce or partially replace imported basil oils. Export opportunities with the same products need also to be explored. The production of new types of basil oils rich in specific chemical constituents that have application in new products will require a close relationship with both essential oil brokers and end-processors.

REFERENCES

*Journal Paper No. 12,017, Purdue Univ. Agr. Expt. Sta., West Lafayette, IN 47907. This research was supported in part by a grant from the Purdue University Agricultural Experiment Station (Specialty Crops Grant No. 014-1165-0000-65178.
Table 1. Chemotaxonomic classification of selected Ocimum species.

Ocimum spp. Predominate constituents Reference
basilicum linalool methyl chavicol Guenther 1949
linalool, methyl cinnamate Guenther 1949
methyl chavicol Guenther 1949
methyl chavicol linalool Guenther 1949
canum camphor, limonene Xaasan 1981
methyl cinnamate, linalool Guenther 1949
citriodorium citral Darrah 1974
gratissimum eugenol Sobti 1979
thymol Guenther 1949
kilimandscharicum camphor Baslas 1968
1,8-cineole Ntezurubanza 1984
micranthum 1,8-cineole, ß-caryophyllene, elemenes, eugenol Charles et al. 1990
sanctum eugenol Philip 1985
eugenol, ß-caryophyllene Philip 1985
methyl eugenol ß-caryophyllene Lawrence 1972
suave eugenol Chogo 1981
trichodon eugenol Ntezurubanza 1986
viride thymol Ekundayo 1986

Table 2. Chemotaxonomic classification of selected Ocimum spp. based on the USDA germplasm collection.z

Ocimum spp.
PI Number or cultivar name		 Predominant constituents Country of origin
basilicum
175793 linalool Turkey
368699 linalool 1,8-cineole Yugoslavia
358465 linalool geraniol Yugoslavia
174285 linalool methyl chavicol Turkey
190100 methyl chavicol linalool Iran
253157 methyl chavicol citral Iran
170579-spsy methyl cinnamate, and Z isomer Turkey
170579 methyl cinnamate, methyl chavicol, linalool Turkey
Purdue selection methyl eugenol Thailand
canum
500945 camphor (1-S) Zambia
500942 camphor (1-S), 1,8-cineole Zambia
500947 1,8-cineole, ß-pinene Zambia
500953 1,8-cineole, camphor (1-S) Zambia
500950 1,8-cineole, methyl cinnamate Zambia
citriodorium
Manglak citral, geraniol and isomer Thailand
gratissimum (var. suave)
211715 eugenol, ocimene (cis-b) Taiwan
sanctum
Ka-prow eugenol, ß-caryophyllene, ß-elemene Thailand
unknown species
414205 ocimene (trans-b), (ß-bisabolene) USA
zData of Quinn and Simon, Purdue University (unpublished).
ysps = single plant selection

Table 3. The major essential oil constituents in basils cultivated in the USA.z

Cultivar Major essential
oil compounds		 % of total
essential oils
'Anise' methyl chavicol 47
linalool 30
'Bush' linalool 35
eugenol 16
1,8-cineole 8
Dark Opal' linalool 62
eugenol 5
1,8-cineole 5
'Lemon' geranial 29
neral 21
geraniol 7
linalool 7
'Picollo' linalool 61
eugenol 16
'Spice' eugenol 30
ocimene 17
methyl chavicol 6
'Sweet Basil' linalool 7-59
methyl chavicol 5-29
eugenol 2-12
'Sweet Fine' linalool 57
eugenol 17
zData of Simon and Quinn, Purdue University, unpublished, 1985.

Fig. 1. Common sweet basil (Ocimum basilicum L.) cultivated in the U.S. s a fresh culinary herb and dried spice.

Fig. 2. Germplasm collection of Ocimum spp. at the Purdue University Vegetable Research Farm Lafayette, Indiana.

Fig. 3. Commercial harvest of Comoro basil oil in northern Indiana.

Last update September 5, 1997 aw