Basil – Ocimum basilicum
Part used: aerial parts
Ocimum basilicum L. is a half-hardy annual or short-lived perennial, which is native to India and Asia and cultivated worldwide. It is very variable in morphology. Erect, branching, green stems (to 60 cm) support opposite, soft, bright-green oval leaves, which are slightly crumpled-looking. Whorls (usually six flowers) of small, white, lipped, tubular flowers are borne in terminal racemes. The fruit contains four small smooth black seeds. It is propagated from seed.
Many cultivars and varieties are used and some are cultivated, especially for the manufacture of pesto. Simon et al (1999) compare the growth habit and constituents of 42 forms cultivated in the USA, and note that the cultivars of var. purpurescens contain a substantial concentration of anthocyanins.
Crosses can occur between any Ocimum basilicum varieties, cultivars and related species such as Ocimum minimum L. There is substantial variation in composition of the volatile oil and little correlation has been found between phenotype and chemotype or genotype and chemotype. Schnaubelt (1999) uses basil as an example of the broad range of healing qualities in aromatic oils, and associates this with the adaptability and vigour of the plant kingdom.
Volatile oil accumulates in trichomes so yield depends on leaf number and size. Concentration of volatile oil in basil cv. Sweet Genovese was higher after cultivation at 25°C than at 15°C.
Drying and freezing resulted in loss of concentration and changes in the proportion of each component. A substantial reduction from 0.3 to 0.1 % was found in the concentration of volatile oil in dried basil after 6 months of storage at 4°C in aluminium polyethylene polyamide bags. This was originally a high methylchavicol sample, but the reduction in concentration of methylchavicol from 0.15 to 0.01% after storage, associated with relative increases in monoterpenes, oxygenated monoterpenes and sesquiterpenes, led to important changes in the volatile oil. Similar results are discussed by Grayer et al (1996).
A study of drying methods found that, compared to oven drying at 45°C, air-drying resulted in lower loss of volatile oil and greater retention of the more floral odour of fresh basil. However, the authors argue that oven-drying produced a better product as deterioration could occur over the time-span of air-drying.
Most people know basil today. It is used in cuisines across the world, from Thai to Italian, and particularly the famous pesto sauce from Genoa. We may mention it in the same breath as oregano and bay or imagine how we make use of the fresh and not the dried plant, as we do with coriander or parsley. It must be one of the most frequent pot herbs, sitting in sunny kitchen windowsills across many lands and in many times, as Fuchs records in 16th century Germany and Bauhin in the 17th regarding the reports of scorpions commonly making their homes under pots in Venice.
Yet look in any modern English-language herbal and the chances are that basil will not appear in it. Go back 70 odd years to Maud Grieve’s A Modern Herbal, and you will find an entry for basil, with an etymological link to the Greek ‘basileus’ meaning ‘king’ and descriptions of several varieties of this ‘regal’ herb, but no indications or uses! We must agree with Quincy that basil is found in few herbal prescriptions, the only one in his day being the College of Physicians’ compound briony water used for hysterical conditions, and with Miller that although the herb has a fragrant scent – fit for the palace was Fuch’s assessment of the smell of the ‘basilikon’, as it was known by the German apothecaries – it is little used in medicine. Apparently the internal use of basil was condemned by the Ancients.
Culpeper gives us a reasonably accurate description and more information on this sweet or garden basil. This herb of virulent qualities has stirred up argument among the authorities: ‘Galen and Dioscorides hold it not fitting to be taken inwardly… Pliny and the Arabian physicians defend it’. Pliny actually gives us both sides of the argument, taking Chrysippus’ many criticisms and countering them one by one on the testimony of later writers and physicians. It is not true, Pliny writes, that goats, who eat most things, avoid it. Nor does it make a man witless and bring on lethargy, for a perfume of basil and vinegar is used to bring someone round from a faint or to rouse a person from indolence. Basil vinegar is also good for the stomach, and to break wind upwards, to treat jaundice and dropsy and applied to the belly, to stop (bloody) diarrhoea. It has a diuretic effect, also, and other actions agreed on since the death of Chrysippus three centuries earlier: in the head region a liniment of basil corrects cold in the head, clears catarrh, and with vinegar and oil of roses or myrtle helps headache; the powdered seed is taken as snuff to provoke sneezing to clear the head, or the juice made up with goose grease and dropped into children’s ears for problems there. It can be applied to eyes watering with irritation or inflammation. Externally, mixed with a copper compound, it removes warts. Eaten at table with vinegar, the herb strengthens the female womb and can be used to repress breast milk when it is time to wean the child.
Pliny relates without comment the superstitions he has read in Chrysippus concerning basil: that the bruised herb placed under a stone will breed a serpent; or the herb chewed and put in the sun will breed worms and maggots; that basil pounded with crabs or crayfish will attract all the scorpions of the area to gather around the bait; or finally, that if you are stung by a scorpion on a day when you have eaten basil, you will surely die! Pliny has made it clear that basil possesses medicinal qualities, including that of treating scorpion stings (despite Beck’s translation of Dioscorides (II 141) which supports Chryssipus’ assertion and is credited to the Libyans), when applied externally with wine and vinegar, but how we make sense of some of them is another matter. Can the herb warm and comfort a cold head but also cool and refresh someone in a burning fever? If the herb has some aphrodisiac effect, how does it also repress the rage of choler, the yellow bile humour whose dominance can induce lust?
Culpeper considers the herb to be hot and moist in the first degree. This is a category of Galenic pharmaceutical activity that allows the plant to be used in heating and in cooling prescriptions. Its effect is therefore implicitly balancing or tonic, reducing heat to the body’s normal level or cherishing heat where it is lacking. Culpeper, however, limits its actions to a strengthener of the womb, perhaps as an aid to conception, but certainly of help in delivery of the foetus and expulsion of the placenta in labour, and thus not to be taken during pregnancy, for fear of abortion. He thus characterizes the herb more by its sympathy and antipathy to this organ by making it a herb of Mars in Scorpio, which ‘as it helps the deficiencies of Venus in one kind, so it spoils all her actions in another’. This designation also reflects the association of the plant with scorpions but obscures its reputed cordial effect of heating the heart (which he listed in his Catalogues of simples in the new dispensatory, in the second edition of the Pharmacopoeia Londinensis (1669)). He adds instead that it can be applied to poisonous bites and wasp and hornet stings for it will quickly draw the venom to it and ‘all poisons draw their like’. Finally, it is observed not to survive alongside rue in the garden, and rue ‘is as great an enemy to poison as any grows’. He advises a dosage not above half a drachm (2 g) and ends saying he dare not write any more about it.
Culpeper is hardly promoting basil as a medicinal herb but he exceeds Parkinson, who opines from the first that basil has little application in medicine and is employed rather as a sweet-smelling herb, especially since Dioscorides and Galen think it should not be given internally. Here in Parkinson is the conventional warning about dimness of sight, from too much consumption of basil, and of the plant containing superfluous moisture (hot and moist in the second degree, according to Galen), which would prove harmful to the body over time, if consumed. Topical applications are acceptable: for worms in the belly and for reducing a swollen spleen; snake bites and scorpion stings; the juice with goose grease for earache in children; Pliny’s combination with oil of roses and vinegar for lethargy, jaundice and dropsy; the sternutatory action mentioned by Dioscorides and the smell of basil vinegar to repress the tendency to faint; finally, the moistening quality of the plant to help ripen abscesses and pustules, as Galen suggested. Bock, cited by Bauhin, also adds others: that the seed dissolved in rose water and gum overnight is useful for mouth ulcers and other inflammations, chapping of the lips and warts on the breasts. Parkinson knows basil only as a garden plant, reckoning its natural habitat unknown, but he does mention the cordial uses noted by the Arabic writers, in a trembling of the heart or palpitations and for melancholy or sadness, and he explains an aphrodisiac quality with reference to the herb being given to horses to help them breed. He must have read Bauhin’s reference to comments by Simeon Seth that basil helps the heart, changing the grief of the soul caused by black bile into cheerfulness and joy, and the head, procuring sleep when steeped in water and drunk.
Dosage: Culpeper does not go beyond a dose of 2 g of herb, although it is not clear whether fresh or dry is meant. Ibn Sina has a dose of 106 g of the juice, which seems excessive given the safety concerns voiced below. Other historical authors do not specify dosage. Miele et al (2001) estimate that a portion of pesto might contain as much as 10 g of fresh basil with a volatile oil content of 0.5%, therefore a fresh tincture 1:3 of basil taken in a dose of up to 5 mL three times daily delivers half this quantity of fresh herb and should remain within the bounds of safety as far as the ingested levels of methyl eugenol are concerned. We propose this dose, which is 1 mL larger than Menzies-Trull’s dose of a tincture of unspecified strength and type, as the upper limit of dosage range for specific tincture of basil. Bartram suggests 2 teaspoons of fresh basil or 1 teaspoon of dried as an infusion, with not more than 3 cups taken daily. We advise that herbalists monitor carefully the responses to basil administered within these dosage ranges in order to better establish dose-related benefits, possible side-effects such as diarrhoea and with the purpose of better clarification of an effective and safe dosage range.
Total 0.4-1.1%, terpenes; oxygenated terpenes: linalool 15.6-32.2%; sesquiterpenes: bergamotene 1-20.2%; phenylpropanoids: methyl chavicol 0-4.2%, eugenol 0-22.2% (fresh, five cultivars, cultivated, Czech Republic)
Terpenes; oxygenated terpenes: linalool 0-85.4%, 1,8-cineole 0.4-13.8%; sesquiterpenes; phenylpropanoids: methyl chavicol 0-88.3%, eugenol 0-38.5% (16 samples, three varieties, one cultivar, cultivated, UK).
Total 0.3-0.9%, terpenes: myrcene 0-0.9%, oxygenated terpenes: linalool 41.2-76.2%; sesquiterpenes: bergamotene 0-3.4%, cadinol 1.8-7.5%; phenylpropanoids: methyl chavicol 0-41.4% (10 cultivars, Italy).
Total 0.4-1.5%, terpenes; oxygenated terpenes: linalool 2.7-60.2%, citral 0-65.6%; sesquiterpenes; phenylpropanoids: methyl chavicol 0-74.3%, methyl eugenol 0-34.2%, methyl cinnamate 0-63.1 % (18 samples, cultivated, Turkey).
Oxygenated monoterpenes: linalool 19-37.6%, 1,8-cineole, 7.1-14.2%; phenylpropanoids: methyl chavicol 8.5% (one sample only), eugenol 3.3-24.4% (fresh, nine cultivars, including five used for pesto, cultivated, Italy).
Linalool 0-50%, 1,8-cineole 0-8.2%, geraniol 0-14.2%, methyl chavicol 0-93.4%, methyl eugenol 41.8% (two samples) (18 samples, cultivated, Spain).
Linalool 0-3.2%, methyl chavicol 83.8-88.6% (five samples, cultivated, Togo).
Some volatile constituents are also found as aglycones.
The volatile oil combines both terpenoids such as linalool and phenylpropanoids such as methyl chavicol (estragole). The composition varies with geographical origin and time of harvest. Five chemotypes are identified by Grayer et al (1996): high linalool, high methyl chavicol, linalool/methyl chavicol, linalool/eugenol, methyl chavicol/methyl eugenol. These categories were supported with the addition of linalool/methyl eugenol by Pascual-Villalobos & Ballesta-Acosta (2003). Methyl cinnamate is an important component is some samples, and a study in Turkey identified somewhat different categories: high linalool (mean 48%), high methyl chavicol (mean 68%), linalool 23%/methyl cinnamate 30%, high methyl cinnamate (mean 61%), methyl eugenol, high citral (mean 61%), methyl chavicol 42%/citral 34%. In addition, a study of O. basilicum, O. minimum, O. americanum and O. x citriodora identified five categories – high linalool, high methyl chavicol, linalool/methylchavicol, high methyl cinnamate, citral/spathulenol – and showed that the categories did not correspond with the species (26 samples, cultivated, USA).
The linalool 0.3-67.7% was found to be pure (/?) (-)-linalool in 11/12 samples, and in 10/11 purchased oils whereas, in Ocimum sanctum the main enantiomer was (5)(+)-linalool (12 samples, cultivated, 11 purchased oils, Israel).
Ursolic acid, oleanolic acid (Nicholas 1958).
Total 2.3- 6.5% (measured as gallic acid equivalents): rosmarinic acid (23 samples, Iran).
Recommendations On Safety References
1. Use caution with oil of basil and do not use during pregnancy and lactation.
Culpeper claims that basil is emmenagogue. Price & Price (1995) review different opinions and advise avoiding use of the aromatherapy oil in pregnancy and lactation.
2. Although basil contains constituents whose safety is under review as they have been found to be carcinogenic in animal studies, there is no evidence that this poses a risk in humans.
The phenylpropanoid volatile oils in basil are methyl chavicol (estragole), methyl eugenol and eugenol which are phenyl methyl ethers, also referred to as alkenylbenzenes. Another phenyl methyl ether, safrole, has been shown to be carcinogenic in animal tests which are reviewed by Tisserand & Balacs (1995). Safrole has been found to form DNA adducts in rats and to be present in the tissues of smokers with oesophageal carcinoma who also chewed betel Areca catechu, which contains safrole.
Methyl eugenol has also been found to form DNA adducts. However, there are different viewpoints on the safety of methyl eugenol and estragole in foods, which depend on differing interpretation of the animal studies. The opinion of the Scientific Committee on Food (2001) of the European Commission is that the use of foods and spices containing methyleugenol and estragole should be reduced as no lower threshold of safety can be determined. However, other experts argue that the effects are dose dependent and that the low levels in diet are not a significant risk. Rietjens et al (2008) present a model for risk assessment which attempts to calculate a margin of exposure and concludes that methyl eugenol is a low priority for risk management. In any risk assessment, there may be groups who are at particular risk, and Miele et al (2001) discuss this possibility in people who eat substantial quantities of pesto. The main cultivar used for pesto cv. Genovese Gigante can contain high levels of methyl eugenol. Twenty-two pots of young plants from one batch of seeds, all in the same soil, were distributed to 11 sites in Northern Italy. After 4 weeks, the concentration of methyl eugenol in the oils showed marked variation, from 10.6 to 100%, and eugenol was the other main constituent. The conclusion was that it would be safer to use plants higher than 16 cm, which are higher in eugenol as concentration of methyleugenol is higher in young plants below 6.5 cm.