Evaluation

Various pharmacopoeial procedures are given for the evaluation of volatile oils. Odour and taste are obviously important in the preliminary examination; however oils should not be tasted neat but only after dilution with a sugar solution in ethanol as prescribed in the BP. Physical measurements including optical rotation, relative density and refractive index are regularly employed for identification and

assessment of purity; similarly thin-layer chromatograms. Capillary gas chromatographic profiles are used to determine the proportions of individual components of certain oils. Advances in gas chromatography have now made possible the ready determination of the chirality of particular components of volatile oils thus detecting adulteration with synthetic material or unwanted other oils; examples of its use are carvone in caraway oil, linalol in coriander oil and linalol and linalyl acetate in neroli oil. The ketone and aldehyde contents of oils such as caraway and lemon respectively are determined by reaction with hydroxylamine hydrochloride (oxime formation) and titration of the liberated acid. Other general tests described in the BP include examination for fixed and resinified oils (residue after evaporation), foreign esters (conversion to a crystalline deposit) and presence of water (turbidity of a carbon disulphide solution).

There have been a number of recent problems (1999) with the occurrence of tetrachloromethane in essential oils, particularly spearmint oil. This is probably not due to deliberate adulteration (the adulterant is present at low ppm levels) but a consequence of cleaning the drums before use with offending solvent and inefficient removal of it before filling the drums. Unfortunately on detection it renders the oil useless, as in food tetrachloromethane is prohibited.

The volatile oil content of crude drugs is commonly determined by distillation (Chapter 16).

Biogenesis

The origin of metabolites with phenylpropane and terpenoid structures has been discussed in Chapter 18. In medicinal essential oils the number of the former is limited but for the monoterpenes which arise at the geranyl pyrophosphate (GPP) level of terpenoid synthesis there are numerous examples. Analyses show that these oils commonly contain 40–80 monoterpenoids, many in relatively small proportion. A major constituent of one oil may be a minor one in another.

Three groups of monoterpenoid structures are involved: (1) acyclic or linear; (2) monocyclic; and (3) bicyclic. In the plant they are sequentially derived from limonene in this order as illustrated in Fig. 22.1. Relatively few enzymes, termed cyclases, appear to determine the skeletal class (e.g. menthanes, pinanes, thujanes etc.) and it is possible that these serve as rate-limiting enzymes. However, regulatory factors for the control of synthesis operate not only at the biosynthetic enzyme level per se but in a hierarchical manner up to the whole-organism level.

Fig. 22.1 Possible biogenetic relationships between some monoterpene types.

Because of the trans geometry of the double bond at the C-2 of GPP, direct cyclization to limonene is not possible and for Mentha spp. it has been shown that (−)-limonene synthase located within the oil glands catalyses the isomerization of GPP to enzyme-bound (+)-3S-linalyl pyrophosphate with subsequent cyclization to (−)-limonene. However, many enzymatic steps are involved in the subsequent modifications and interconversions of these monoterpenes. Some components of volatile oils are sesquiterpenes (C₁₅H₂₄) (q.v.) and they include cadinene, zingiberene (structure, Fig. 18.17) and caryophyllene. The formulae of some of the more common constituents of pharmaceutical volatile oils are given in Fig. 22.2.

Fig. 22.2 Some components of pharmaceutical oils.

It is increasingly evident that some monoterpenes and other components of volatile oils also occur in plants in the glycosidic form. Thus, geraniol, nerol and citronellol occur as glycosides in the petals of Rosa dilecta, thymol and carvacrol as glucosides and galactosides in Thymus vulgaris and eugenol, benzyl alcohol, β-phenylethyl alcohol, nerol, geraniol and geranic acid as glucosides in Melissa officinalis. It is considered that these glucosides of monoterpenols and of 2-phenylethanol are translocated from leaves to flowers as aroma precursors.

Table 22.1 may be used to compare the compositions of important volatile oils. The classification is arbitrary, since an oil may contain a number of compounds all about equally important but belonging to different chemical classes. The substance used for classification is not necessarily the one present in greatest amount. Thus, nutmeg is classified on its myristicin and lemon on citral, although these constituents form only a small percentage of these oils.

Table 22.1 Composition of volatile oils.

C₂₀ or diterpenoid compounds include such resin acids as (+)- and (−)-pimaric acid and their isomer, the abietic acid of pine resin. The abietane acids have antimicrobial, antiulcer and cardiovascular properties (for a review covering some 56 acids over the period 1967–92 see A. S. Feliciano et al., Planta Med., 1993, 59, 485). Many diterpenoids (e.g. vitamin A and gibberellic acid) do not belong to the volatile oil–resin group. Similarly, only a small proportion of triterpenoid compounds (C₃₀) are found as resin constituents (e.g. in Euphorbia resinifera).

Extraction of oils used in perfumery

Certain oils used in perfumery, such as oil of rose, are prepared by steam distillation as described above but many of the flower perfumes require other treatment. An important centre for the extraction of flower oils is Grasse, in the south of France. Here the oils are extracted by enfleurage, by digestion in melted fats, by pneumatic methods or by means of solvents. In the enfleurage process glass plates are covered with a thin layer of fixed oil or fat upon which the fresh flowers are spread. The volatile oil gradually passes into the fat and the exhausted flowers are removed and replaced by a fresh supply. Formerly the flowers had to be picked off by hand but this is now done mechanically. Only a small percentage of the flowers, which resist the action of the machine, require removal by the fingers or by means of a vacuum cleaner. The pneumatic method, which is similar in principles to the enfleurage process, involves the passage of a current of warm air through the flowers. The air, laden with suspended volatile oil, is then passed through a spray of melted fat in which the volatile oil is absorbed. In the digestion process the flowers are gently heated in melted fat until exhausted, when they are strained out and the perfume-containing fat is allowed to cool. It will be seen that in each of the above processes the volatile oil has now been obtained in a fatty base. The volatile oil is obtained from this by three successive extractions with alcohol. The alcoholic solutions may be put on the market as flower perfumes or the oil may be obtained in a pure form by recovery of the alcohol. Solvent extraction is based on the Soxhlet principle (see Chapter 16).

Macroscopical characters

All the mints have square stems and creeping rhizomes. The flowers are arranged in verticillasters and have the floral formula K(5),C(5),A4,G(2). The black mint, which is the one most commonly cultivated in England, has purple stems and dark green petiolate leaves which are tinged with purple. The leaf blades are 3–9 cm long and have a grooved petiole up to 1 cm long. They have a pinnate venation with lateral veins leaving the midrib at about a 45° angle, acuminate apex and sharply dentate margin. Glandular trichomes can be seen as bright yellowish points when the lower surface is examined with a hand lens. The leaves are broader than those of M. spicata (spearmint), but narrower than those of M. aquatica (water mint). The small, purple flowers appear in late summer.

Microscopical characters

The microscopy of peppermint leaves is typical of the family, showing numerous diacytic stomata on the lower surface (Fig. 42.2G), three- to eight-celled clothing trichomes with a striated cuticle (Fig. 42.4C), and two types of glandular trichome, one with a unicellular base and small single-celled head and the other with a multicellular head characteristic of the family (Fig. 42.5E). Calcium oxalate is absent.

There is a 5% limit of stems over 1 mm in diameter for the official leaves, and as mints are very susceptible to most diseases, there is a 10% limit of leaves infected by Puccinia menthae.

Of commercial importance has been the development by mutation breeding at the A. M. Todd Co. of a strain of Mitcham peppermint resistant to the wilt disease Verticillium albo-duram var. menthae. The strain retains the Mitcham cultivar organoleptic characteristics and gives a good oil production in verticillium-prone soils where cultivation with the ordinary varieties is impossible.

Biogenesis of peppermint monoterpenoids

The biosynthetic isoprenoid origin of monoterpenes was mentioned at the beginning of this chapter. As the essential oils of the Labiatae are synthesized in the cells of the glandular trichomes, techniques such as cell and root culture are of little value as experimental tools. However, new procedures, using gentle abrasion of leaf surfaces with glass beads, have been developed for isolating in high purity and excellent yield, peltate glandular trichomes of peppermint which retain their biosynthetic activity.

Developmental changes in the oil composition of the leaves include the disappearance of limonene, the accumulation of 1,8-cineole, the conversion of menthone to menthol and the acetylation of menthol. All these processes begin at the distal extremity of the leaf and shift progressively to the leaf base (B. Voirin and C. Bayer, Phytochemistry, 1996, 43, 573).

A proposed pathway for the formation of monoterpenes in peppermint is given in Fig. 22.3. A number of enzymes involved in the reactions have been characterized. The hydrolase system involving (−)-limonene-3-hydroxylase in the formation of the alcohol (−)-trans-isopiperitenol is cytochrome-P450-dependent and is associated with the oil gland microsomal fraction. The remaining steps are catalysed by operationally soluble enzymes of the oil cells. It will be noted that (+)-pulegone is a branching point for the formation of menthol stereoisomers.

Fig. 22.3 A possible biogenetic scheme for some monoterpenoids of Mentha × piperita.

Japanese peppermint oil is derived from Mentha canadenis var. piperascens; it contains 70–90% menthol, for the extraction of which it is largely used. The commercial dementholized Japanese oil contains approximately the same amount of menthol and its esters as the American oil.

Characters

Mint has more or less crumpled, opposite, ovate-lanceolate leaves, 3–7 cm long. The apex is acute or acuminate, and the margin unequally serrate. The leaves differ from those of peppermint in that they are almost sessile and have a bright green colour free from purple.

Constituents

Oil of spearmint contains (−)-carvone, (−)-limonene, phellandrene and esters. As with M. × piperita limonene is the precursor of the monoterpenoids and in this case the action of a (−)-limonene-6-hydroxylase predominates to give the alcohol (−)-trans-carveol which is oxidized to carvone (Fig. 22.4). Dihydrocarvone is formed later in the season and is absent from plantlets produced by shoot-tip culture. Again like peppermint, oil production is influenced by the age of plant, time of collection, chemical varieties and hybridization.

Fig. 22.4 Biosynthetic pathway for major constituents of spearmint oil.

Macroscopical characters

The petiolate oblong-lanceolate leaves are up to 10 cm length and 2 cm in breadth, greenish-grey on the upper surface and tomentose on the lower with a markedly reticulate venation. The leaf apex is rounded, the base rounded or cordate and the margin crenulate. The odour and taste are characteristically pungent.

Microscopical characters

The upper epidermal cells have beaded anticlinal walls, the lower ones are thin-walled and sinuous; both epidermi possess diacytic stomata. Glandular trichomes of the typical labiate type occur on both surfaces with rarer uniseriate glandular trichomes having a double- or single-celled head. Clothing trichomes are numerous, particularly on the lower surface, composed of a short thickened basal cell with articulated and bent terminal cells. A few single-celled warty-walled trichomes are present. The long protective trichomes serve to distinguish S. officinalis from S. sclarea and S. pratensis (M. Then et al., Acta Pharm. Hung., 1998, 63, 163).

Constituents

The volatile oil of sage contains about 50% of α- and β-thujone together with cineole, borneol and other constituents (Fig. 22.2). Varieties and other species of sage contain differing amounts of thujone.

Non-volatile components of the leaf include diterpenes, phenolic glycosides based on caffeic and p-hydroxybenzoic acids (for recent isolations see M. Wang et al., J. Nat. Prod., 1999, 62, 454), and tannins.

Action and uses

Sage as an infusion is used as a mouthwash and gargle for its antiseptic and astringent action. Recent attention has focused on the cholinergic activity of the drug and its possible role in the treatment of Alzheimer’s disease and memory loss. It is interesting to note that long before recent advances in the understanding of the neurobiology of Alzheimer’s disease, plant materials including sage and balm (Melissa officinalis) were recommended in old reference books as possessing memory-improving properties (see E. K. Perry et al., J. Pharm. Pharmacol., 1999, 51, 527). The phenolic glycosides of sage together with those of Melissa officinalis and Lavandula angustifolia possess antioxidant properties (J. Hohmann et al., Planta Medica, 1999, 65, 576).

Constituents

The compositon of the essential oil is considered under ‘Rosemary Oil’, below. Hydroxycinnamic acids include caffeic acid and a dimer rosmarinic acid (a characteristic metabolite of the subfamily Saturejoidae to which Rosmarinus belongs). For the dried leaf, the BP sets a minimum requirement of 3.0% for total hydroxycinnamic acids expressed as rosmarinic acid.

In recent years, a large number of phenolic abietane diterpenoids have been recorded for the leaves including the potent antioxidant carnosic acid together with its degradation products carnosol, rosmanol, epirosmanol and 7-methylepirosmanol. For new recently isolated diterpenes, see A. A. Mahmoud et al., Phytochemistry, 2005, 66, 1685; C. L. Cantrell et al., J. Nat. Prod., 2005, 68, 98. Triterpenes include the alcohols α- and β-amyrin, ursolic acid and oleanolic acid.

In vitro cell cultures of rosemary have been produced which biosynthesise carnosic acid, carnosol and rosmarinic acid (A. Kuhlmann and C. Rohl, Pharm. Biol., 2006, 44, 401).

Uses

Rosemary leaves have many traditional uses based on their antibacterial, carminative and spasmolytic actions.

Constituents

The volatile oil composition of thyme can vary enormously and various chemotypes have been recorded, particularly regarding thymol and carvacrol. The official drug is required to contain not less than 1.2% volatile oil, of which not less than 40% consists of thymol and carvacrol. It is these phenols that are largely responsible for the antiseptic, antitussive and expectorant properties of the drug. Other common variables of the oil are cymene (10–24%) and γ-terpinene (4–18%). Two extreme variations recorded are an almost complete lack of thymol and carvacrol in T. vulgaris and an oil containing 74% thymol from T. zygis.

A number of monoterpenoid glycosides occur in the leaves, particularly glucosides and galactosides of thymol and terpineol; seven new such constituents have recently been described (J. Katajima et al., Phytochemistry, 2004, 65, 3279; Chem. Pharm. Bull., 2004, 52, 1013). Flavones, highly oxygenated flavones, flavanones and dihydroflavonals may be responsible for the spasmolytic effect of the leaves, and the biphenyls reported in 1989 may have deodorant properties. Other constituents include rosmarinic acid (see ‘Rosemary’) up to 2.6%, various acids, tannins and resins. Rosmarinic acid and 3′-O-(8″-Z-caffeoyl) rosmarinic acid have been reported as the most important radical scavengers of the leaves (A. Dapkevicins et al., J. Nat. Prod., 2002, 65(6), 892).

Uses

Although in Britain oregano is not used medicinally to any extent, its thymol content gives it strong antiseptic properties. Traditionally its uses include the treatment of digestive disorders, pharnygeal infections and mild fevers.

Uses

Although it is the volatile oil of lavender that is principally used for medicinal purposes the BHP 1983 cites flatulent dyspepsia, colic and depressive headache as indications for use of the flowers. It may be used in combination with other drugs such as rosemary, valerian, meadow-sweet and others.

Lavender oil types

The taxonomy of the lavenders is confusing and Continental oils differ among themselves owing to the fact that a number of different species, varieties and hybrids are distilled. The true lavender, L. officinalis, yields the best oil when grown at a fairly high altitude, the variety growing under these conditions being known as ‘petite lavande’. At a lower altitude the ‘lavande moyenne’ yields a somewhat less esteemed oil. ‘Grande lavande’, L. latifolia Villers (L. spica DC), yields a much coarser oil, which is sold as oil of spike. The above plant readily hybridizes with L. officinalis yielding a plant known as ‘grosse lavande’ or ‘lavandin’, the oil of which is intermediate in character between that of the parent forms. According to Tucker (Baileya, 1981, 21, 131), of the many names applied to this hybrid species, the correct one is L. × intermedia Emeric ex Loiseleur. As hybrids the plants do not breed true and are normally propagated vegetatively; a simple efficient method for the in vitro shoot regeneration from the leaves has offered possibilities for future breeding (S. Dronne et al., Plant Cell Reports, 1999, 18, 429). The lavandin oil market is controlled by the French with Spain the principal producer.

The evergreen plant flowers from July to September and the fresh flowering spikes yield about 0.5% of volatile oil. The amount varies according to variety, season and method of distillation; modern steam stills give a rather larger yield than those in which the flowers are boiled with water. Genuine Continental lavender oil normally contains over 35% of esters. Oil of spike, which is largely used in cheap perfumery, contains little ester but a high proportion of free alcohols (about 23–41% calculated as borneol); 30 components have been identified. The nature of the alcohols also varies from a mixture of linalol and geraniol in the best lavender oil to borneol in oil of spike. Hybrids are of intermediate character (e.g. ‘lavandin oil’) and contain about 6–9% of esters and about 35% of alcohols. An analysis of the Spanish oil (J. de Pascual Teresa, Planta Medica, 1989, 55, 398) enabled the identification of 50 compounds, the principal ones being 1:8-cineole, linalol and camphor; in contrast to the oil of L. angustifolia, linalyl acetate was not present.

A GC profile together with prescribed percentage ranges of 10 components of the pharmaceutical oil is given in the BP/EP; linalol (20–45%) and linalyl acetate (25–46%) are the principal constituents with a maximum limit for camphor of 1.2%. Chiral chromatography is used to determine the chiral purity of the linalol and linalyl acetate contents.

As with other Labiatae, Lavandula cell cultures do not produce essential oil and for L. vera rosmarinic acid is the principal phenolic component together with caffeic acid and traces of others. An enol ester of caffeic acid is a blue pigment also found in cell cultures (see E. Kovatcheva et al., Phytochemistry, 1996, 43, 1243).

Species of Lavandula other than the above are also cultivated. L. stoechas has a markedly different odour and of its 51 volatile components, fenchone, pinocaryl acetate, camphor, eucalyptol and myrthenol predominate. Large producers are Spain and France. Oil from wild plants growing in the Algiers region of Algeria contained as significant constituents fenchone (31.6%), camphor (22.4%), p-cymene (6.5%) lavandulyl acetate (3.0%) and α-pinene (1.0%). Fifty-four components amounting to ca 73% of the oil were identified (T. Dob et al., Pharm Biol., 2006; 44, 60).

Uses

Lavender oil is principally used in the toiletry and perfumery industries and occasionally in ointments, etc., to mask disagreeable odours. It is employed pharmaceutically in the antiarthropod preparation Gamma Benzene Hexachloride Application. Lavender flowers are included in the BHP and are indicated for the treatment of flatulent dyspepsia and topically, as the oil, for rheumatic pain. The oil is extensively used in aromatherapy (q.v.).

History

Caraway fruits were known to the Arabian physicians and probably came into use in Europe in the thirteenth century.

Macroscopical characters

The commercial drug (Fig. 22.5) usually consists of mericarps separated from the pedicels. The fruits are slightly curved, brown and glabrous, about 4–7 mm long, 1–2.3 mm wide and tapered at both ends; they are crowned with a stylopod often with style and stigma attached. Each mericarp shows five almost equal sides, five narrow primary ridges, and, when cut transversely, four dorsal and two commissural vittae. They have a characteristic aromatic odour and taste.

Fig. 22.5 Caraway. A, mericarps showing attachments to carpophore; A₁, mericarp sectioned longitudinally to show position of embryo; A₂, mericarp side view (×8). B, transverse section of mericarp (×50); C, portion of vitta isolated by alkali maceration (×25); D, sclereids of mesocarp; E, endosperm cells with micro-rosette crystals of calcium oxalate; F, endocarp layer in surface view (all ×200). c.m, commissural meristeles; em, embryo; en, endosperm; end, endocarp; mc, mesocarp; r, three of five primary ridges; ra, position of raphe; s, stylopod; s.c, secretory canal; t, testa; v, vitta; v.b, vascular bundle with associated finely pitted sclerenchyma.

Microscopical characters

A transverse section of a caraway mericarp (Fig. 22.5) shows five primary ridges, in each of which is a vascular strand with associated pitted sclerenchyma and having a single secretory canal at the outer margin of each. The six vittae which appear somewhat flattened and elliptical in transverse section may attain a width of 350 μm; they extend from the base of the fruit to the base of the stylopod. They are lined with small, dark reddish-brown cells and contain a pale yellow or colourless oleoresin (Fig. 22.5B, C). The raphe lies on the inner side of the endosperm, which is non-grooved. Occupying the majority of the transverse section is the endosperm, with thickened cellulose walls (having also deposits of a β-(1,4)-mannan as a reserve polysaccharide) and containing fixed oil and aleurone grains having one or two microrosettes of calcium oxalate. The embryo, which is situated near the apex of the mericarp, will only be seen in sections passing through that region.

More detailed examination shows that the outer epidermis of the pericarp is glabrous (cf. aniseed) and has a striated cuticle (cf. fennel). The mesocarp consists of more or less collapsed parenchyma and lacks the reticulated cells of fennel. The endodermis (or inner epidermis of the pericarp) (Fig. 22.5F) consists of a single layer of elongated cells, arranged more or less parallel to one another and not showing the ‘parquetry’ arrangement of coriander.

Constituents

Caraway contains 3–7% of volatile oils (BP not less than 3.0%), 8–20% of fixed oil, proteins, calcium oxalate, colouring matter and resin.

Uses

Large quantities of caraway fruits are used for culinary purposes. The fruits and oil are used in medicine for flavouring and as carminatives. The carminative and antispasmodic properties have been experimentally verified.

Macroscopical characters

The drug usually consists of separate, broadly oval mericarps, about 4 mm long and 2–3 mm broad. The fruits are very much compressed dorsally, the two central ridges being prolonged into membranous wings, while the dorsal ones are inconspicuous. The fruits have an aromatic odour and taste similar to those of caraway.

Microscopical characters

Each mericarp has four vittae on the dorsal surface and two on the commissural. The outer epidermis has a striated cuticle (distinction from fennel), and the mesocarp contains lignified, reticulate parenchyma (distinction from caraway). The endosperm is much flattened but otherwise resembles that of caraway.

Constituents

The volatile oil (Dill Oil BP/EP) resembles oil of caraway in containing carvone and limonene. The European fruits yield about 3–4% of volatile oil, which should contain from 43 to 63% of carvone; the carvone content is determined by reaction with hydroxylamine hydrochloride (oxime formation) and titration of the liberated acid. Other constituents reported for the oil include trans- and cis-dihydrocarvone, trans- and cis-carveol, limonene, D- and L-dihydrocarveol, α- and γ-terpinene, α-phellandrene and others. Chemical types based on the proportion of carvone present, and the presence or absence of dillapiole and myristicin have been distinguished.

Monoterpene glycosides have been isolated from the water-soluble fraction of the fruits.

For further details on constituents, see T. Ishikawa et al., Chem. Pharm. Bull., 2002, 50, 501; M. Kosar et al., Pharm. Biol., 2005, 41, 491.

Uses

Like caraway, dill is used as a carminative and flavour; it is much used in infant’s gripe water.

Allied drug

Indian Dill, derived from a variety of A. graveolens consists of whole cremocarps which bear pedicels and are narrower and less compressed than the European drug. Indian dill oil contains dillapiole and less carvone.

Macroscopical characters

The drug (Fig. 22.6A) usually consists of the whole cremocarps, which, when ripe, are about 2.3–4.3 mm diameter and straw-yellow. Each consists of two hemispherical mericarps united by their margins. Considerable variation exists in coriander. The Indian variety is oval, but the more widely distributed spherical varieties vary in size from the Ukrainian 2.3–3.7 mm to the Moroccan 4.0–4.3 mm. The apex bears two divergent styles. The 10 primary ridges are wavy and inconspicuous; alternating with these are eight more prominent, straight, secondary ridges. The fruits have an aromatic odour and a spicy taste. They are somewhat liable to insect attacks.

Fig. 22.6 Coriander. A, Whole fruit (×8); B, transverse section of fruit (×16); C, fragment of epicarp in surface view with stoma and small prismatic crystals of calcium oxalate; D, endosperm cells with microrosette crystals of calcium oxalate; E, layers of sclerenchyma from the mesocarp; F, lignified parenchyma of the mesocarp and underlying endodermis showing ‘parquetry’ arrangement (all ×200). a, line of attachment of mericarps; b, sepal; c, carpophore, c.s, commissural surfaces; c.v, commissural vitta; en, endosperm; end, endodermis; par, lignified parenchyma of mesocarp; p.r, primary ridge; ra, raphe; r.v, remains of dorsal vittae; s, stylopod; scl, sclerenchyma; s.r, secondary ridge; t, testa.

Microscopical characters

A transverse section of a fully ripe fruit shows only two mature vittae in each mericarp, both on the commissural surface (Fig. 22.6B). The numerous vittae present in the immature fruit on the dorsal surface of each mericarp gradually join and are eventually compressed into slits. The outer part of the pericarp, which possesses stomata and prisms of calcium oxalate, is more or less completely thrown off. Within the vittae-bearing region of the mesocarp a thick layer of sclerenchyma is formed, which consists of pitted, fusiform cells. These sclerenchymatous fibres tend in the outer layers to be longitudinally directed and in the inner layers to be tangentially directed. In the region of the primary ridges more of the fibres are longitudinally directed; in the secondary ridges nearly all are tangentially directed. Traversing the band of sclerenchyma and corresponding in position to the primary ridges are small vascular strands composed of a small group of spiral vessels. The mesocarp within the sclerenchymatous band is composed of irregular polygonal cells with lignified walls. The inner epidermis of the pericarp is composed of ‘parquetry’ cells, which in the powder are often seen united to the cells of the inner mesocarp. The testa is composed of brown flattened cells. The endosperm is curved and consists of parenchymatous cells containing fixed oil and aleurone grains. The latter contain rosettes of calcium oxalate 3–10 mm diameter (see Fig. 22.6 C–F).

Constituents

Coriander fruits contain up to 1.8% of volatile oil according to origin (BP/EP standard not less than 0.2%). The distilled oil (Coriander Oil BP/EP) contains 65–70% of (+)-linalool (coriandrol), depending on the source, and smaller amounts of α-pinene, γ-terpinene, limonene and p-cymene together with various non-linalool alcohols and esters. Some 40 constituents have been identified. The BP/EP uses GC for the evaluation of the oil with linalool and geraniol as internal standards; there is also a test for chiral purity ((R)-linalool, maximum 14%). Other constituents isolated from the fruits include flavonoids, coumarins, isocoumarins, phthalides and phenolic acids. T. Ishikawa et al. (Chem. Pharm. Bull., 2003, 51, 32) obtained 33 compounds from the water-soluble fraction of a methanolic extract of the fruits; new constituents included monoterpenoids, monoterpenoid glycosides, monoterpenoid glucoside sulphates and aromatic compound glycosides. The high content of fats (16–28%) and protein (11–17%) in the fruits make distillation residues suitable for animal feed. The fruits yield 5–7% of ash.

The unripe plant has an unpleasant, mousy odour, which is also present in oil distilled from unripe fruits (mainly aldehydes such as n-decanal contained in peripheral vittae). Marked changes occur in volatile oil composition during ontogenesis; the peripheral vittae flatten and lose their oil, all of which is then produced by the commissural vittae. During ordinary storage of the fruits, the oil composition undergoes considerable alteration.

Uses

Very large quantities of the spice are produced in many countries for domestic purposes, such as for use in curries. In the former USSR linalool is isolated from the oil as starting material for other derivatives. Pharmaceutically coriander and its oils are used as a flavouring agent and carminative.

Macroscopical characters

The drug (Fig. 22.7A) consists of greyish-brown, pear-shaped, somewhat compressed cremocarps, which are usually attached to pedicels 2–12 mm in length. The cremocarps are 3–6 mm long and 2–3 mm broad. The Spanish (Alicante) and Italian are distinguished by their large size and light colour, while the German and ‘Russian’ are smaller, more ovoid and darker. Each mericarp has five somewhat wavy ridges and is slightly pubescent on the dorsal surface. They have an aromatic odour and a sweet, aromatic taste.

Fig. 22.7 Aniseed. A, Side view of cremocarp showing line of attachment to the two mericarps (×8); B, transverse section of mericarp (×25); C, covering trichomes of epicarp (×200); D, branched and unbranched vittae isolated by alkali maceration (×25). a, Line of attachment of mericarps; c, carpophore; c.s, commissural surfaces; c.v, commissural vitta; en, endosperm; e.t, epicarp bearing trichomes; m, meristele; mc, mesocarp; r, three of five primary ridges of one mericarp; ra, raphe; s, stylopod; v, vittae.

Microscopical characters

Microscopical examination shows that the epidermis bears numerous papillae and unicellular hairs. On the dorsal surface of each mericarp are from 15 to 45 branched vittae. A small amount of vascular tissue and reticulated parenchyma is present. The endosperm is slightly concave on the commissural surface and contains protein and fixed oil (see Fig. 22.7B–D).

Constituents

Anise fruits yield 2–3% of volatile oil (BP/EP2.0%), which is almost identical with that obtained from star-anise fruits. A number of water-soluble constituents have been isolated from the fruits including various glucosides, see E. Fujimatu et al., Phytochemistry, 2003, 63 (5).

Aniseed Oil

BP/EP tests and standards for the oil include: TLC identification of anethole and anisaldehyde; maximum limit of 0.1% for fenchone and 0.01% for foeniculin; trans-anethole 87–94%; estragole 0.5–5.0%, anisaldehyde 1.0–1.4% and linalol <1.5% determined by gas chromatography.

Star anise oil

The essential oil should contain 87–94% trans-anethole, 0.5–5.0% of estragole and smaller amounts of anisaldehyde (0.1–0.5%) and foeniculin (0.1–3.0%); other minor components include chavicol methyl ether (an isomeride of anethole), p-methoxyphenylacetone, safrole and other minor components. The oil is, for all ordinary purposes, indistinguishable from that of P. anisum but differences in the gas chromatographic profiles can be seen. The oil is liable to atmospheric oxidation and both anisic aldehyde and anisic acid are normally present. This change is said to diminish the tendency of the oil to solidify, which it normally does on cooling to about 15°C. In the past, the oil was imported in lead containers and some pharmacopoeias give a limit test for heavy metals.

Both aniseed oil and star anise oil are used as flavouring agents and as carminatives. Anethole (a colourless crystalline solid m.p. 21°C) may be prepared from the oil or manufactured synthetically.

History

The bitter orange tree appears to have been introduced from northern India into eastern Africa, Arabia and Syria, whence it was brought to Europe by either the Arabs or Crusaders about AD 1200. The sweet orange was not known in Europe until the fifteenth century and appears to be of Chinese origin.

Collection and preparation

Orange peel may be prepared in the Mediterranean countries or in England. The peel should be removed with as little of white ‘zest’ as possible. Hand-cut, English dried peel is most esteemed. The peel may be removed in four ‘quarters’, or in a spiral band. It is also found in thin strips, similar to those found in marmalade, cut by machines. The so-called Maltese is of this type, which is known as ‘gelatin-cut’. Fine slicing causes the rupture of a large number of oil glands and some loss in aroma.

Characters

The colour of the dried peel is somewhat variable, but frequently reddish-brown in the spiral form and greenish-brown in the ‘quarters’. The other surface is rugged, being somewhat raised over the oil glands, which are clearly seen in sections with the naked eye. The inner surface bears a small amount of white ‘zest’. Fragrant odour; aromatic and very bitter taste.

Microscopic examination shows a small-celled epidermis with characteristic stomata; parenchyma containing prismatic crystals of calcium oxalate 20–45 mm long, or sphaerocrystalline masses of hesperidin; small anastomosing vascular bundles; and large oil-filled cavities usually arranged in two irregular rows.

Constituents

Dried bitter orange peel contains not less than 2.0% of volatile oil, vitamin C and the flavonoid glycosides hesperidin and neohesperidin. The latter, present to the extent of 5–14% in the unripe peel, gradually disappears on ripening.

Citrus glycosides and limonoids

Citrus fruits contain a large number of flavanone glycosides. The best-known of these, hesperidin (see Fig. 21.18), was first isolated in 1828. It is present in oranges, both bitter and sweet, and in lemons. See also ‘Flavone and Related Flavonoid Glycosides’ and ‘Hesperidin and Rutin’. An isomer of hesperidin, neohesperidin, is present in certain samples of Seville oranges. Naringin, present in some Seville oranges, is the chief flavonoid constituent of the grapefruit. Coniferin (Table 21.1) has been reported in C. sinensis and may add to the effects of limonin and naringin.

The bioproduction of neohesperidin and naringin in callus cultures of C. aurantium has been demonstrated (J. A. del Río et al., Plant Cell Rep., 1992, 11, 592).

Uses

Bitter orange peel is used as a flavouring agent and as a bitter tonic. Hesperidin in the soluble form as in the fresh fruit functions as vitamin P.

Collection and preparation

Lemons are collected in January, August and November, before their green colour changes to yellow. They are exported in cases containing from 200 to 360 fruits. The smaller fruits, which would not have a ready sale, are used in the preparation of oil of lemon. The peel is removed with a sharp knife in the form of a spiral band.

Characters

Dried lemon peel occurs in spiral bands up to 2 cm wide and 2–3 mm thick. Some pieces bear the apex of the fruit, which has a nipple-like appearance. The outer surface is rough and yellow; the inner surface is pulpy and white. Odour, strong and characteristic; taste, aromatic and bitter. The anatomical structure closely resembles that of orange peel (q.v.).

Constituents

Dried lemon peel contains not less than 2.5% of volatile oil (see below), vitamin C, hesperidin and other flavanone glycosides, mucilage and calcium oxalate. Lemon peel is mainly used for flavouring purposes.

History

Both expressed and distilled oils of lemon were sold in Paris as early as 1692. The sponge process as used in Sicily was described by Barrett in 1892. Machines were first introduced for oil of lemon production in 1920 and by 1930 about half the Italian oil was produced by their aid. New machines are being frequently introduced, and although some hand-expressed oil is still made (e.g. for eau de cologne, which requires the highest quality), pharmaceutical oil is now machine made.

Preparation

Oil of lemon is only one of several products made from lemons. In addition to dried peel, much lemon peel is candied with sugar. The pulp of the fruit yields on expression lemon juice, which may be canned or used for the preparation of citric acid and citrates. Pulp residues are used for pectin manufacture and as cattle food.

The following processes are used for the production of oil:

Constituents

Lemon oil contains terpenes (about 94% mainly (+)- limonene), sesquiterpenes, aldehydes (citral, about 3.4–3.6%, and citronellal) and esters (about 1% geranyl acetate). Limonene (see Fig. 22.2) is a liquid, b.p. 175°C. Citral (see Fig. 22.2) or geranial, a liquid, b.p. 230°C, is the aldehyde corresponding to the alcohol geraniol. Lemon oil shows a marked tendency to resinify and should be protected from the action of air and light as much as possible. It has been shown by the use of GC and TLC that the oil obtained directly from the oil glands of the rind by capillary insertion differs from the fresh and stored commercial oils in composition. Principal reactions which cause these changes are oxidations of monoterpenes, aldehydes and esters, peroxide formation, polymerizations and isomerizations (e.g. limonene → α-terpinene).

Adulteration

Oil of lemon was at one time frequently adulterated with oil of turpentine, but analysts now have to contend with more scientific methods of adulteration. These include the addition of terpenes obtained in the preparation of ‘terpeneless oil of lemon’ and the addition of the cheaper distilled oil of lemon. The value of the oil is judged to some extent on the citral content, but a normal citral content alone is not a sure indication of purity, since citral may be added from a cheaper source such as oil of lemon-grass, which contains 75–85% of this aldehyde. It will be gathered that a careful examination of the oil by both physical and chemical methods is necessary, as exemplified by the standards and tests given in the BP.

Uses

Oil of lemon is used for flavouring and in perfumery.

History

Nutmegs and mace appear to have been first introduced into the Levant by the Arabs in the middle of the twelfth century and by the end of that century were found in northern Europe. The native country of the nutmeg (the Molucca or Spice Islands) was known to Arabian writers of the thirteenth century, and the Banda Islands, a group of the Moluccas where the plant is very abundant, were discovered by the Portuguese in 1512. The Portuguese, after holding the spice trade for about a century, lost it to the Dutch, who maintained a complete monopoly by destroying the trees in neighbouring islands and preventing the export of living seeds. The ordinary drying process destroys the vitality of the seeds, but they were also soaked in milk of lime for many weeks and were seldom sold until they were several years old. The Spice Islands were occupied by the English for a few years (1796–1802), during which period the opportunity was taken to start cultivation in Penang and Sumatra. Until the trees so planted reached maturity the effect of the Dutch restriction was still felt, and in 1806 the import price of mace in London was as high as £10 kg⁻¹.

Cultivation of the spice was subsequently introduced to the West Indies and during the Second World War production of nutmegs in Grenada was expanded enormously. In 1955 a hurricane destroyed 90% of the trees but the industry has now recovered and nutmegs remain the island’s main commodity export.

Cultivation, collection and preparation

Nutmeg trees can be grown from fresh seed sown in the shell. The seeds germinate in about 5 weeks, and when the young plants are about 6 months old, they are transplanted to the fields. When the sex can be determined (5–8 years), the male trees are reduced to about 10% of the total. This method leads to irregularly spaced trees in the plantation and now in Grenada vegetative propagation of the female trees is performed by marcotting or air layering. In this, female shoots are split but not detached, and by the use of hormone powder and suitable packing of the wound, are induced to root. This takes 4–18 months after which the rooted shoots are detached and brought on before planting out. A success rate of over 40% for rooting is now obtainable. Another technique which has been used to increase the number of female trees is the employment of approach grafts. The trees bear fruit from their eighth or ninth year and continue to fruit well for about 20–30 years. The peach-like fruit splits when ripe, exposing the seed with its lobed, red arillus. The plant fruits almost continuously and two or three crops are collected annually. In the East the fruits are collected by hand or by means of a hooked stick, but in Grenada the fruits are allowed to fall to the ground. The orange-yellow pericarp which is about 12.5 mm thick, is usually removed on the spot. Later the arillus is picked off and constitutes, when dried, mace. From mature plantations the annual yield per acre is about 250–500 kg of nutmeg and about 50–100 kg of mace. The nutmegs are dried in the shells, the procedure differing according to local conditions but usually taking about 3–6 weeks. In Malaya sun-drying is used to some extent, but the seeds require adequate cover at night or in wet weather. Large quantities are dried in ovens and in brick buildings. In the latter the seeds are placed on trays over low charcoal fires, being turned and gradually moved nearer to the fires during the process. When drying is completed, the kernel rattles within the brittle testa, which constitutes about one-quarter of the weight of the seed. The testa is cracked by means of a wooden truncheon, mallet or special machine, and the nutmeg extracted. However, machines are liable to cause bruises, and cracking by hand is preferable. The liming of nutmegs to reduce insect attack is now less commonly practised than in the past. After cracking, the nutmegs are now usually graded abroad into sizes represented by numbers per unit weight. Elongated nutmegs, which fetch a lower price, and small or damaged ones are kept separate. Nutmegs are exported in barrels or cases containing about 50 kg.

Macroscopical characters

Nutmegs are broadly oval in outline, 2–3 cm long and about 2 cm broad. If not heavily limed, the surface is of a brown or greyish-brown colour and is reticulately furrowed. At one end is a light-coloured patch with brown lines radiating from the hilum, which is surrounded by a raised ring. From this an ill-defined furrow (imprint of the raphe) runs to the chalaza, at the opposite end of the kernel, where there is a small dark depression. Odour, strong and aromatic; taste, pungent and slightly bitter.

A longitudinal section (Fig. 22.9C) has a lustrous, marbled appearance. The outer tissue, which consists of dark brown perisperm, penetrates the light brown endosperm, the infoldings branching and giving rise to the marbled appearance. The perisperm possesses fibrovascular bundles, the position of which is indicated by the reticulate furrows found on the outer surface.

Fig. 22.9 Myristica fragrans. A, Fruit with half of the pericarp removed; B, nutmeg (dried kernel); C, longitudinal section nutmeg; D, transverse section nutmeg (all × 1). a, Aril (mace); ch, chalaza; e, endosperm; e.c, cavity left by embryo; f.p, fleshy pericarp; g, groove marking line of raphe; m, micropyle region; p, perisperm; t, testa.

Microscopical characters

The outer perisperm cells are radially flattened and have brownish contents, insoluble in potassium hydroxide or chloral hydrate. A few of the cells contain prismatic or disc-shaped crystals, thought to consist of potassium acid tartrate. The inner perisperm shows numerous extensive lamellae, corresponding to the furrows on the surface, and penetrating into the endosperm. These lamellae are composed of parenchymatous cells with thin brown walls and of oval oil cells, and show in their outer part vascular strands composed of lignified spiral vessels. The endosperm is composed of parenchymatous cells, with thin brown cell walls, and containing simple or 2–10 compound starch grains (individual grains up to 22 μm in diameter, globular or irregular in shape, with sometimes a slit-like hilum); aleurone grains, the larger of which show a well-defined crystalloid; and feathery crystals of fat. A few tannin cells, containing tannin and starch, occur scattered in the endosperm.

Allied drugs

Papua nutmegs are derived from M. argentea, a tree grown in New Guinea. They are often taken to Macassar and enter commerce as Macassar, Papua, long or wild nutmegs. They have a uniform, scurfy surface, little odour and a disagreeable taste.

Bombay nutmegs are derived from M. malabarica, grown in India. They are very long and narrow and lack the characteristic aroma of the genuine drug.

Mace

Common mace or Banda mace consists of the dried arillus or arillode of M. fragrans. This, when fresh, is of a bright red colour and is removed either by the finger or a knife. When removed entire, it forms‘double blade’ mace, but if in two pieces, it is known as ‘single blade’ mace. After flattening by treading under the feet or pressing between boards the mace is slowly dried. The volatile oil of mace resembles that of nutmeg, the major phenolic compounds isolated being dehydrodiisoeugenol and 5′-methoxydehydrodiisoeugenol, both of which have a significant antibacterial action. In recent years a series of lignans and neolignans has been isolated from mace; see Table 21.7 for the formula of macelignan.

Bombay mace is a regular article of commerce, although almost valueless as a spice. It is dark red in colour, is lacking in aroma and yields about 30% of extractive to light petroleum (genuine mace yields about 3.5%). Papua mace is distinguished by its shape, dull brownish surface, lack of aroma and acrid taste.

Constituents

Nutmegs yield 5–15% of volatile oil and also contain 30–40% fat, phytosterin, starch, amylodextrin, colouring matter and a saponin. They yield about 3% of total ash and about 0.2% of acid-insoluble ash. The psychotropic properties of nutmeg are discussed under ‘Hallucinogens’.

Uses

Nutmegs, maces, and their oils are largely used for flavouring and as carminatives. In traditional Indian medicine an aqueous extract of nutmeg is used for the treatment of infantile diarrhoea.

History

Cassia bark was known to the Chinese in 2700 BC but it is not until the thirteenth century that any reference is found to the collection of cinnamon in Ceylon. Ceylon was occupied by the Portuguese in 1536, the Dutch in 1656, and the English East India Company in 1796. Cinnamon cultivation was started by the Dutch in 1770 and they exercised a strict monopoly comparable with their monopoly of nutmegs. This was continued until the monopoly of the English East India Company was abolished in 1833.

Cultivation, collection and preparation

In Sri Lanka about 26 000 acres are devoted to cinnamon plantations. Most of the plantations are small and are situated in the southern or western provinces. Sri Lanka and the Seychelles both export large quantities of cinnamon leaf oil.

The production of the characteristic compound quills of the inner bark is a multistage process and was fully described and illustrated in earlier editions of this book. Briefly, the cinnamon plants are grown from seed and coppiced almost to the ground when 2 or 3 years old. About five or six shoots are allowed to grow from the stump and are kept vertical by pruning. After about 18 months of growth, and when some 3 m long and 2 cm diameter, shoots are harvested, trimmed and, following a few hours ‘fermentation’, they have the bark removed with a non-ferrous knife. The peeled bark is then stretched over a suitable stick and the outer cork and cortex scraped off with a curved scraper. Individual pieces of scraped bark are then placed one inside the other and built up to a length of about 42 in (c. 106 cm). The compound quills are dried on wooden frames in the open air without exposure to direct sunlight and then finally sorted into grades and made into compact bales of about 45 kg.

The traditional grades of cinnamon are designated: 00000, 0000, 000, 00, 0, 1, 2, 3, 4, quillings, featherings, chips. Most commercial material corresponds to Nos. 1–4 grades. Quillings and featheringsconsist of small pieces, the latter often containing some outer bark; they are used for grinding and for oil distillation. Chips consist mainly of outer pieces of bark, and the oil derived from them has a lower specific gravity and a lower aldehyde content than that from the inner bark.

Macroscopical characters

Cinnamon is imported in large bundles about 1 m in length. Retailers generally receive their supplies in shorter lengths known as ‘cigar lengths’. The drug consists of single or double compound quills about 6–10 mm diameter and of varying length (Fig. 22.10). In the different grades the thickness of each piece of bark varies considerably, but in good-quality cinnamon it is usually not more than about 0.5 mm, while the number of pieces of bark forming the compound quill varies from about 10 to 40. The external surface of each piece is yellowish-brown and shows longitudinal shining, wavy lines (pericyclic fibres) and occasional scars and holes (indicating the positions of leaves or twigs). The inner surface is somewhat darker and longitudinally striated. The bark breaks with a short, splintery fracture. Odour is fragrant; taste, warm, sweet and aromatic.

Fig. 22.10 Cinnamon. A, Compound double quill (× 0.5); B, transverse section (×50); C, elements of the powder (×200). ck, Cork cells; cr, acicular crystals of calcium oxalate; l.f, laminated fracture of compound quill; m.r, medullary ray; o.c, oil cells; o.t, remains of outer tissues; p.f, pericyclic fibres; ph.f, phloem fibres; r.ck, residual patches of cork; s, scar of twig; sc, sclereids; sc.l, sclereid layer of pericycle; s.q, transverse surface of compound quill; st, starch granules.

Microscopical characters

Transverse sections of cinnamon (Fig. 22.10) show under the microscope a complete absence of epidermis and cork. Shrivelled remains of cortex occur in patches. The outer limit of the bark is marked by a pericycle composed of a continuous ring of three to four layers of sclereids with small groups of pericyclic fibres embedded in it at intervals. The latter produce the lighter-coloured, wavy, longitudinal lines on the outside of the commercial bark. The sclereids (Fig. 22.10) have thickened lignified walls, showing well-defined pit-canals. The thickening on the outer walls is often less pronounced than on the radial and inner tangential walls. The lumen is clearly visible and sometimes contains starch. The pericyclic fibres range from 1000 to 2500 μm long and have strongly thickened lignified walls showing stratification and pit-canals. Primary phloem cannot be distinguished. The secondary phloem is composed of phloem parenchyma containing oil and mucilage cells; phloem fibres; and medullary rays. The sieve-tube tissue, embedded in the phloemparenchyma, is often obliterated. The phloem parenchyma is composed of thin-walled cells, with yellowish-brown walls, and contains starch in compound and simple grains, the latter not exceeding 10 μm diameter (those of Cinnamomum cassia often exceed this figure) and numerous acicular crystals of calcium oxalate about 5–8 μm long. Some of the phloem parenchyma cells contain tannin. The secretion cells, containing volatile oil or mucilage, are two or three times the diameter of the phloem fibres, and are axially elongated. The phloem fibres, which occur isolated or in tangential rows, are more abundant towards the inner part of the bark. They are usually less than 30 μm in diameter (those of C. cassia measure 30–40 μm in diameter) and have a length of 200–600 μm. The thick lignified walls show stratification. The secondary phloem is divided up by the radial medullary rays, which are uni- or biseriate near the cambium but become broader towards the outside by tangential growth of the cells. The rays are 7–14 cells high. The medullary ray cells are radially elongated, thin-walled with yellow–brown cell contents containing numerous acicular crystals of calcium oxalate. For illustrations of the powdered elements, see Fig. 22.10.

Constituents

Cinnamon contains volatile oil (BP/EP not less than 1.2%), phlobatannins (which have been little investigated compared with those of cassia) mucilage, calcium oxalate and starch.

Allied drugs

Cayenne cinnamon consists of the bark of cultivated plants of Cinnamomum zeylanicum grown in French Guiana, Brazil and some of the islands of the West Indies. It is generally obtained from older branches than the Ceylon drug and appears to be inferior to it in quality. It is not used to any extent in Britain.

C. loureirii is commercially important in Vietnam and grows in the mountainous districts of Annam. The plant, which is closely related to C. cassia is also found in China and Japan. It resembles cassia bark more closely than cinnamon, and occurs in quills up to 30 cm long, 4 cm wide and 0.5–7.0 mm thick. The outer surface is greyish-brown, warty and ridged. The odour is coarser than that of Ceylon cinnamon and the taste sweeter.

Uses

Cinnamon is used as a flavouring agent and mild astringent. The oil has carminative properties and is a powerful germicide.

Preparation

The best yield of camphor is obtained from old trees. The wood is cut into chips and treated with steam, when a solid sublimate of camphor and liquid volatile oil pass into the receiver. The volatile oil is treated to yield more camphor and much of the residual camphor oil is used as a source of safrole. The impure camphor is treated with lime and charcoal and resublimed into large chambers. It collects in the form of ‘flowers of camphor’, which can be made into the familiar blocks by hydraulic pressure. Camphor can also be prepared from suitable leaves of the tree and their use is helping to reduce the complete destruction of camphor tree forests.

Synthetic camphor is largely prepared from American turpentine. By the action of hydrogen chloride the pinene is converted into bornyl chloride which, on treatment with sodium acetate, yields isobornyl acetate. Hydrolysis of this is to isoborneol and subsequent oxidation gives camphor.

Tests for identity and purity of natural camphor are important to eliminate synthetic racemic material, excess camphor oil, and camphors from inappropriate natural sources. These tests include melting point (175–179°C), specific optical rotation (+40.0 to +43.0), acidity and limit of halogens (particularly chlorides arising from the synthesis of racemic camphor), gas chromatographic detection of extraneous material arising from the synthesis of camphor and other sources including α- and β-pinene, cineole, fenchone, fenchol and borneol.

Characters

Camphor occurs in small, colourless crystals or in transparent fibrous blocks. It has a characteristic odour and a pungent, aromatic taste, which is followed by a sensation of cold. It volatilizes at ordinary temperatures, forming an encrustation on the walls of the vessel in which it is kept.

Camphor oil (see above) contains, in addition to camphor, safrole, borneol, heliotropin, vanillin and terpineol, a number of sesquiterpene alcohols. Oil of Pakistan origin has been shown to contain 25 monoterpenoids, and four chemotypes with respect to oil composition have been recorded for Vietnamese material.

Allied drugs

Borneo camphor, obtained from Dryobalanops aromatica (Dipterocarpaceae), and Ngai camphor, obtained from Blumea balsamifera (Compositae), are used in China and Japan. In California laevorotatory camphor is produced from species of Artemisia (Compositae).

Uses

Camphor is used externally as a rubefacient, and internally as a mild antiseptic and carminative. It finds many non-pharmaceutical uses. Large quantities were once used in the manufacture of celluloid.

History

Cloves were used in China as early as 266 BC and by the fourth century they were known in Europe, although very expensive. The Spice Islands were occupied by the Portuguese at the beginning of the sixteenth century, but they were expelled by the Dutch in 1605. As in the case of nutmegs, the Dutch made every effort to secure a monopoly, destroying all the trees in their native islands (Ternate, Tidor, Mortir, Makiyan and Bachian) and cultivating them only in a group of small islands, of which Amboyna is the largest. In 1770, however, the French succeeded in introducing clove trees into Mauritius, and cultivation was afterwards taken up in Sumatra (1803), Penang, Cayenne, Madagascar, Zanzibar (1818), Pemba and elsewhere.

Collection and preparation

The flower buds are collected when their lower part turns from green to crimson. In Zanzibar and Pemba collection takes place twice yearly, between August and December. The inflorescences are collected from movable platforms. The cloves are dried in the open air on mats and separated from their peduncles, the latter forming a separate article of commerce known as ‘clove stalks’ (Fig. 22.12D). If left too long on the tree, the buds open and the petals fall, leaving ‘blown cloves’; later the fruits (Fig. 22.12C) known as ‘mother cloves’ are produced. A small proportion of these, usually at a stage intermediate between that of a clove and a fully ripe fruit, are frequently found in the drug. Cloves are imported in bales covered with matting made from strips of coconut leaves.

Macroscopical characters

Cloves are 10–17.5 mm long (cf. A and B in Fig. 22.12). The Penang and Amboyna varieties are the largest and plumpest and are most esteemed, but they are in such demand in the East that relatively small quantities of them reach Europe; they are used principally for the making of pomanders. The Zanzibar variety, however, is of good quality, although smaller and leaner than the Penang and of a blackish-brown rather than a reddish-brown colour.

The ‘stalk’ of the clove consists of a cylindrical hypanthium or swelling of the torus, above which is a bilocular ovary containing numerous ovules attached to axile placentae. The ‘head’ consists of four slightly projecting calyx teeth; four membranous, imbricated petals, and numerous incurved stamens around a large style (Fig. 22.12E).

Cloves have a strong, fragrant and spicy odour and a pungent, aromatic taste. When indented with the fingernail, they readily exude oil. Cloves sink in freshly boiled and cooled water (distinction from cloves which have been exhausted of volatile oil).

Microscopical characters

The hypanthium, in the region below the ovary, shows in transverse section (Fig. 22.12) a heavy cuticularized epidermis in which occur stomata, slightly raised above the surface and showing well-defined substomatal spaces. Within this is a zone of roughly radially arranged parenchymatous cells containing numerous schizolysigenous oil glands arranged in two or three more or less intermixed layers. The oil glands are ellipsoidal in shape, with the long axis radial, and show an epithelium composed of two or three layers of flattened cells. The contents of the oil glands are soluble in alcohol and are blackened by treatment with alcoholic ferric chloride or osmic acid. The ground mass of parenchyma also gives the blackening with ferric chloride. Cluster crystals of calcium oxalate (5–25 μm in diameter) occur in many of the parenchymatous cells. Within the oil gland layer is a zone of cells with somewhat thickened walls, embedding a ring of bicollateral vascular bundles. The ground tissue of this zone contains cluster crystals of calcium oxalate. The meristeles are enclosed in an incomplete ring of lignified fibres; the xylem is composed of 3–5 lignified spiral vessels. Within the ring of vascular bundles is a zone of aerenchyma composed of air spaces separated by lamellae one cell thick, which supports the central columella. The ground tissue of the columella is parenchymatous and is particularly rich in calcium oxalate clusters. In the outer region of the columella is a ring of some 17 small vascular bundles.

The hypanthium, in the region of the ovary, shows epidermis, oil gland layer and ring of bicollateral bundles. Within this is a zone of cells with very strongly thickened cellulose walls, limited internally by an inner epidermis forming the wall of the ovary. The dissepiment of the ovary is parenchymatous; the placentae are rich in cluster crystals and contain vascular bundles. If sections of the hypanthium are mounted in a concentrated solution of potassium hydroxide, acicular and radiately aggregate crystals separate, owing to the presence of the phenol eugenol in the oil.

The sepals and petals have a simplified leaf structure. The mesophyll parenchyma contains calcium oxalate and embeds numerous oil glands. The epidermis of the sepals shows stomata. The epidermis of the petals is devoid of stomata and is composed of very irregular cells.

The stamens are composed of filament, connective and anther. The filament shows an epidermis of longitudinal elongated cells, a ground mass of parenchyma embedding numerous oil glands and a single vascular strand enclosed in a sheath of crystal cells. The vascular strand is continuous into the connective, which is terminated by an oil gland. The fibrous layer of the anther wall is composed of cells showing spiral bands of lignified thickening. The pollen grains are triangular in outline and 15–20 μm diameter. The style and stigma yield similar characters to those of the filament. See Fig. 22.12 for the illustrated characters of the powder.

Starch, prisms of calcium oxalate and lignified sclereids are absent from a powder consisting of the flower buds only. Clove stalks contain lignified sclereids (Fig. 22.12P) and reticulately thickened xylem vessels. Clove fruits (‘anthophylli’, ‘mother cloves’) contain starch. As there is a permissible pharmacopoeial limit (not more than 6%) for these structures in the drug, a few sclereids and starch grains may therefore be found in the powder. There are also limits for deteriorated cloves (2.0%) and other foreign matter (0.5%).

Constituents

Cloves contain about 14–21% of volatile oil (see below), 10–13% of tannin, various triterpene acids and esters, and glycosides of the following: aliphatic and monoterpenoid alcohols, eugenol, isoeugenol, farnesol, nerolidol, sitosterol, stigmasterol and campestrol.

Uses

Cloves are used as a stimulant aromatic, as a spice and for the preparation of the volatile oil. The sesquiterpenes of clove have been cited as potential anticarcinogenic compounds.

Characters

Oil of eucalyptus is a colourless or pale yellow liquid. It has an aromatic and camphoraceous odour; a pungent, camphoraceous taste, which is followed by a sensation of cold. It is required to contain not less than 70.0% of cineole. 1,8-Cineole and o-cresol form a solid complex and the crystallizing temperature of this forms the basis for the official assay of the oil. The Pharmacopoeia also includes a TLC identification test, and tests which limit the content of aldehydes and phellandrene; these eliminate oils containing citronellal and the so-called industrial eucalyptus oils.

Uses

Eucalyptus oil is much used for alleviating the symptoms of nasopharyngeal infections, for treating coughs and as a decongestant. It is taken internally in the form of mixtures, inhalations, lozenges and pastilles and applied externally as ointments and liniments.

History

Ginger has been cultivated in India from the earliest times; the plant is unknown in the wild state. The spice was used by the Greeks and Romans, and was a common article of European commerce in the Middle Ages. It was well known in England in the eleventh century. Ginger was introduced into Jamaica and other West Indian islands by the Spaniards, and a considerable quantity of the drug was sent from the West Indies to Spain as early as 1547.

Cultivation and preparation

Ginger grows well at subtropical temperatures where the rainfall is at least 1.98 m per annum. As the plant is sterile, it is grown by vegetative means. Selected pieces of rhizome (‘seed pieces’ or ‘setts’) each bearing a bud are planted inholes or trenches during March or April, preferably in a well-drained clayey loam. The procedures resemble potato cultivation. Mulching or manuring is necessary as the plant rapidly exhausts the soil of nutrients. When the stems wither, about December or January, the rhizomes are ready for collection. For the scraped drug, after removal of soil the rhizomes are killed by boiling water. They are then carefully peeled, thoroughly washed and then dried in the sun on mats or barbecues. During drying they are turned from time to time and protected during any damp weather. This first drying usually takes about 5 or 6 days. To obtain a whiter product the ginger is again moistened and dried for a further two days, when it is ready for export. It should not be limed.

With some gingers little or no cork is removed (‘coated’ or ‘unscraped’ gingers) and these grades are now also included in the BP/EP; these are sometimes whitened by dusting with calcium carbonate or lime but are eliminated by the BP ash value (not more than 6.0%).

Macroscopical characters

The dried scraped drug (Fig. 22.13) shows little resemblance to the fresh rhizome, owing to loss in weight and shrinkage. It occurs in sympodially branched pieces known as ‘hands’ or ‘races’. These are 7–15 cm long, 1–1.5 cm broad and laterally compressed. The branches arise obliquely from the rhizome, are about 1–3 cm long and terminate in depressed scars or in undeveloped buds. The outer surface is buff-coloured and longitudinally striated or fibrous; it shows no sign of cork. The drug breaks with a short fracture, the fibres of the fibrovascular bundles often projecting from the broken surface. It has an agreeable aromatic odour and a pungent taste.

Fig. 22.13 Ginger. A, Peeled Jamaican rhizome; B, partially peeled African root (both ×0.75); C, diagrammatic transverse section of unpeeled rhizome (×15); D, oleoresin cell with adjacent parenchyma; E, portions of septate fibres; F, G, portions of septate fibres with attached vessels; H, starch; I, cork cells in surface view from unpeeled drug (all ×200). a, Starch granule, side- and end-aspects; ck, cork; ck₁, irregularly arranged cells of outer cork; ck₂, radially arranged cork cells; d, depressed scar; end, endodermis; f, projecting fibres; i.c, inner cortex; ol, oleoresin cells; o.c, flattened cells of outer cortex; p.c, pigment cell; r, ridges produced by vascular bundles; s, septum; s.s, scraped surface; v.b, vascular bundle; v.f.b, vascular bundle with fibrous sheath; v.b.s, ring of small vascular bundles.

In transverse section a lens shows the cortex, a dark line (the pericycle and endodermis, the latter without starch) and the stele with numerous scattered fibrovascular bundles. Similar bundles also occur in the cortex. The bundles appear as greyish points, the smaller yellowish points which can also be seen being secretion cells.

The unscraped rhizome resembles the above in structure but is more or less covered by brownish layers of cork with conspicuous ridges; the cork readily exfoliates from the lateral surfaces but persists between the branches.

Microscopical characters

The unpeeled rhizome, in transverse section (Fig. 22.13C), shows a zone of cork tissue, differentiated into an outer zone of irregularly arranged cells produced by suberization of the cortical cells without division and an inner zone of cells arranged in radial rows and produced by tangential division of the cortical cells. No cork cambium is differentiated. Within the cork is a broad cortex, differentiated into an outer zone of flattened parenchyma and an inner zone of normal parenchyma. The cortical cells contain abundant starch grains. These are almost entirely simple, ovoid or sack-shaped, are 5–15–30–60 μm long and have a markedly eccentric hilum (Fig. 22.13H). Scattered in the cortex are numerous oil cells, with suberized walls enclosing yellow–brown oleoresin. The inner cortical zone usually contains about three rings of collateral, closed vascular bundles. The larger bundles are enclosed in a sheath of septate, non-lignified fibres. Each vascular bundle contains phloem, showing well-marked sieve-tubes and a xylem composed of 1–14 vessels with annular, spiral or reticulate thickening. These vessels do not give a marked lignin reaction with phloroglucinol and hydrochloric acid. Axially elongated secretion cells with dark contents occasionally accompany the vessels. The inner limit of the cortex is marked by a single-layered endodermis free from starch. The outermost layer of the stele is marked by a single-layered pericycle. The vascular bundles of the stele resemble those of the cortex, and are, except for a ring of small bundles immediately within the pericycle, scattered as is typical of monocotyledonous stems. The ground mass of the stele is composed of parenchyma resembling the cortical parenchyma and containing much starch, and numerous oil cells. Cork cells are absent from the scraped drug. (For illustrations of the above features see Fig. 22.13D–H.)

Constituents

Ginger contains about 1–2% of volatile oil (BP/EP1.5%); for the assay, liquid paraffin (10 drops) or other antifoaming agent may be added to the distillation flask. The rhizomes also contain 5–8% of resinous matter, starch and mucilage. Oil of ginger, to which the drug mainly owes its aroma, contains a mixture of over 50 constituents, consisting of monoterpenes (β-phellandrene, (+)-camphene, cineole, citral and borneol), sesquiterpene hydrocarbons (zingiberene, β-bisabolene, (E,E)-α-farnesene, β-sesquiphellandrene and ar-curcumene) and the sesquiterpene alcohol zingiberol. Over 50 volatile constituents of fresh organically grown ginger (fresh Chinese white and Japanese yellow varieties) have been recorded (S. D. Jolad et al., Phytochemistry, 2004, 65, 1937).

The pungency of ginger is due to gingerol, an oily liquid consisting of homologous phenols. The principal one of these is [6]-gingerol (i.e. where n = 4). It is formed in the plant from phenylalanine, malonate and hexanoate (see Denniff et al., J. Chem. Soc. Perkin, I, 1980, 2637).

Smaller amounts of gingerols with other chain-lengths are also present. Similarly, [6]-gingerdiol is accompanied by four analogues which were isolated as minor components of the rhizome by Kikuzaki et al. from the less-polar fractions of the dichloromethane extracts (Phytochemistry, 1992, 31, 1783). The same group also characterized (Phytochemistry, 1991, 30, 3647; 1996, 43, 273) a number of diaryl-heptanoids and a further seven have since been reported from Chinese Z. officinalis (J. Ma et al., Phytochemistry, 2004, 65, 1137). These diarylheptanoids are similar to the curcuminoids present in greater quantity in turmeric (q.v.). A number of diarylheptanones – gingerenones A, B, C and isogingerenone B have been investigated by Endo and colleagues (Phytochemistry, 1990, 29, 797). Other minor components are methylgingediol, gingediacetates, methylgingediacetates and a C₂₀-dialdehyde.

The pungency of gingerol is destroyed by boiling with 2% potassium hydroxide. Boiling with baryta water decomposes it with formation of a phenolic ketone called zingerone and aliphatic aldehydes (mainly normal heptaldehyde). Zingerone also occurs in the rhizome and, like gingerol, is pungent but possesses in addition a sweet odour. Its pungency is destroyed by prolonged contact with 5% sodium hydroxide. Shogaols, components of the oil, represent compounds formed by loss of water from the gingerols and were not thought to be present in the fresh rhizome. However, T.-S. Wu et al. (Phytochemistry, 1998, 48, 1889) have now isolated three new dehydroshogaols from fresh roots purchased from a market in Taiwan. For formulae of ginger constituents see Figure 22.14.

Fig. 22.14 Constituents of ginger.

Varieties

The plant which yields the official ginger is grown in many tropical countries, including India (Cochin, Calicut and Bengal), Africa (Nigeria, Sierra Leone), China, the East Indies, Cochin China, Australia and Florida. The chief varieties in English commerce are the Chinese, Nigerian, Cochin and African.

A number of commercial varieties of root, oleoresin and essential oil are available, seemingly derived from Z. officinale; whether these arise from different chemical races, from differences in cultivation and harvesting techniques or from different climatic conditions is not clear. They vary considerably in sensory characters. Australian oils are characterized by a ‘lemon, citrus-like’ odour. Oil from Fiji has a high citral content and a relatively high content of 1,8-cineole similar to Japanese oil.

Allied drugs

Japanese ginger is derived from Z. mioga. The volatile oil which it contains differs in physical properties from that of the official species and gives the drug a bergamot-like odour. The taste is less pungent than that of Z. officinale and the starch grains are compound and less eccentric.

Preserved ginger consists of young undried rhizomes which are preserved by boiling in syrup. The West Indian variety is made from the official plant, but that from China is said to be obtained from the greater galangal, Alpinia galanga (Zingiberaceae).

Galangal rhizome, now little used in England although employed on the Continent, is derived from the lesser galangal, A. officinarum.

Adulteration

Most of the likely vegetable adulterants can be detected by a routine microscopical examination. Powdered ginger may have been prepared from ‘wormy’ drug, and so attention should be paid to the absence of insect fragments.

Adulteration may also take the form of the addition of ‘spent ginger’ which has been exhausted in the preparation of essence. This may be detected by the official standards for alcohol-soluble extractive, water-soluble extractive, total ash and water-soluble ash.

Exhausted ginger and, more particularly, ginger galenicals may have their pungency increased by the addition of capsicum or grains of paradise. The suspected liquid, or a tincture prepared from the suspected powder, is heated in a water-bath with caustic alkali. The liquid is then evaporated, and the residue acidified with hydrochloric acid and shaken with ether. Some of the ethereal solution evaporated on a watch-glass gives a residue which is not markedly pungent to taste. This test depends on the fact that gingerol is more readily decomposed by alkalis than are capsaicin or paradol.

Uses and actions

Ginger is used as a carminative and stimulant. A US study by Mowrey and Clayson (Lancet, 1982, 1, 655) indicated that powdered ginger may be a more effective antiemetic than dimenhydrinate (Dramamine). The authors suggested that it may ameliorate the effects of motion sickness in the gastrointestinal tract itself, in contrast to antihistamines, which act centrally. Other reports claim that ginger is effective in the control of excessive and uncontrolled vomiting occurring in the first trimester of pregnancy and that it might provide a cheap antiemetic adjunct to cancer therapy (S. S. Sharma et al., J. Ethnopharmacology, 1997, 57, 93).

A considerable number of pharmacological studies involving the digestive, central nervous and cardiovascular systems have been reported for the isolated constituents of ginger. These activities include the potent inhibitory actions of the gingerols against prostaglandin synthetase which correspond with the anti-inflammatory and antiplatelet aggregation properties of the drug. These compounds, together with [6]-shogaol, also produce enhanced gastrointestinal activity with effects on bile secretion. The C₂₀-dial mentioned previously has a cholesterol-biosynthesis inhibitory activity in animal preparations and is assumed to be a HMG-CoA reductase inhibitor (M. Tanabe et al., Chem. Pharm. Bull., 1993, 41, 710). The sesquiterpene hydrocarbons have also been associated with the antiulcer activity of the drug. A strong antibacterial and antifungal action has been demonstrated for a number of the rhizome constituents.

History

Cardamoms are mentioned in the early Sanskrit writings of Susruta, but it is difficult to say with any certainty when they first appeared in Europe. Immense quantities are still used in Hindu festivals. Both Amomum and Cardamomum appear in a list of Indian spices liable to duty at Alexandria, about AD 176–180. The Portuguese navigator Barbosa (1514) appears to have been the first to mention the source of our official drug as the Malabar coast.

Production, collection and preparation

Although wild plants are found in India and Sri Lanka, cardamoms are mainly obtained from cultivated plants. Propagation is by seedlings or vegetatively but the latter gives problems owing to possible infection by mosaic or katte virus. The plant is reed-like, 4 m or more high, and bears long leaves arising from the rhizome. As the capsular fruits on the same raceme ripen at different times and it is important to collect them when nearly ripe and before they split to shed their seeds, it is best to cut off each fruit at the correct stage with a pair of short-bladed scissors. Pickers can, by this method, collect about 5 kg of fruit per day, although collecting all the fruits on one raceme together is naturally quicker. In Sri Lanka and India flowering and fruiting continues for practically the whole year but most of the crop is collected from October to December.

The fruits are dried slowly, either outdoors or in a curing house. Too-rapid drying is to be avoided, as it causes the fruits to split and shed their seeds. Sometimes the capsules are remoistened and further exposed to the sun but this sun-bleaching, although improving the appearance, also increases the number of split fruits. Bleaching may also be done by placing trays of the fruit over burning sulphur. Bleached fruits appear to have become less common and there is now an increased proportion of the unbleached Alleppy and Ceylon greens. The green curing procedure is also used in Guatemala and it has been claimed that enhanced colour retention is obtained by soaking the fruits for 10 min in 2% sodium carbonate solution before drying.

The capsules have the remains of the calyx at the apex and a stalk at the base. These may be removed either by hand-clipping or by machines. The fruits are then graded by means of sieves into ‘longs’, ‘mediums’, ‘shorts’ and ‘tiny’. If they have been sulphur-bleached, they are aired in the open before being packed for export.

Macroscopical characters

The cardamom fruit is an inferior, ovoid or oblong capsule, about 1–2 cm long. The size, shape and surface vary in the different commercial varieties and grades (see below). The apex is shortly beaked and may show floral remains, while the base is rounded and shows the remains of the stalk. Internally the capsule is three-celled, a double row of seeds attached to axial placentas occurring in each cell. In good samples the seeds form about 70% of the total weight. The seeds in each loculus are tightly pressed together and usually separate in a single mass.

Each seed is about 4 mm long and 3 mm broad and somewhat angular. The colour varies from a dark reddish-brown in fully ripe seeds to a much paler colour in the unripe ones. The testa is transversely wrinkled and is covered by a membranous aril. A groove on one side of the seed indicates the position of the raphe and a depression at one end of the hilum. Cardamom seeds have a strongly aromatic odour and a pleasantly aromatic, although somewhat pungent, taste.

Seeds cut longitudinally and transversely and stained with iodine show the aril, testa, perisperm (containing starch) and the endosperm and embryo (both free from starch), as illustrated in Fig. 22.15.

Fig. 22.15 Cardamom fruits and seeds. A, Mysore; B, Alleppy green; C, long, wild native (all × 1); D, transverse section of fruit (×1.5); E, whole seed (about × 4); F, longitudinal section of seed; G, transverse section of seed; H, arrangement of cells in transverse section of seed coat. d, Dissepiment of fruit; p, pericarp; r, raphe; s, seed; t, wrinkled testa; 1, funicle; 2, operculum or embryonic cap; 3, raphe; 4, chalaza; 5, arillus; 6, epidermis of testa; 7, parenchyma layers of the testa; 8, oil cell layer; 9, sclerenchymatous layer of testa; 10, perisperm; 11, endosperm; 12, embryo; 13, haustorium.

Varieties

Mysore fruits have a cream or pale buff colour and a nearly smooth surface. Malabar are usually smaller and have a rather darker and less smooth pericarp. Mangalore resemble the Malabar but are usually more globular and have a rougher pericarp; they occur both bleached and semi-bleached. Alleppy fruits are narrower than the above varieties, have a markedly striated pericarp and vary in colour from greenish-buff to green. Ceylon greens resemble Alleppy, but are generally greener and more elongated. The seeds of the above varieties are almost indistinguishable from one another, and also from the seeds of the long wild native cardamom (see below under ‘Allied drugs’.)

Microscopical characters

Sections of the seed (Fig. 22.15) show a very thin membranous arillus, enveloping the seed and composed of several layers of collapsed cells, yellow in colour and containing oil. The brownish testa is composed of the following layers. (1) An outer epidermis consisting of a single layer of cells rectangular in transverse section, longitudinally elongated and with prosenchymatous end walls in surface view; light yellow in colour and having slightly thick end walls. (2) A single or double layer of parenchymatous cells, elongated at right angles to the long axis of the overlying epidermal cells (see Fig. 22.15H). (3) A single layer of large parenchymatous cells containing volatile oil; in the region of the raphe there are two layers of oil cells separated by the raphe meristele. (4) Several layers of small flattened parenchymatous cells, their structure often partially obliterated. (5) An inner epidermis of sclerenchymatous cells, radially elongated, with anticlinal and inner walls very strongly thickened and reddish-brown in colour. Lumen bowl-shaped and containing a module of silica (see Fig. 22.15H). The operculum or embryonic cap is composed of two or three layers of these sclerenchymatous cells, continuous with those of the inner epidermis. The micropyle is a narrow canal passing through the operculum. Within the testa is a well-developed perisperm composed of parenchymatous cells packed with minute globular starch grains, 4 μm diameter and containing in the centre of each cell a small prismatic crystal of calcium oxalate. The perisperm encloses the endosperm and embryo, both composed of thin-walled cells rich in protein.

Cardamom pericarps or husks which have been used for the adulteration of powdered drugs may be identified in the form of powder by the pitted fibres and spiral vessels of the fibrovascular bundles and by the abundant, empty parenchymatous cells.

Constituents

Samples of cardamom seed yield 2.8–6.2% (BP not less than 4.0%) of volatile oil and also contain abundant starch (up to 50.0%), fixed oil (1–10%) and calcium oxalate.

Cardamom oil

The oil is distilled in relatively limited quantities in Sri Lanka, India and Guatemala with an estimated global production of some 4 tonnes in 1984. The oil contains a high proportion of terpinyl acetate and cineole and smaller quantities of other monoterpenes, including alcohols and esters. Over 40 compounds have been identified in the oils of Elettaria species. The BP requires an ester value of 90–156 and an optical rotation of +20° to +40°. The loss of oil from seeds kept in the pericarp is small but a loss of 30% in 8 months takes place when the seeds are separated from the fruits. Gas chromatography has shown oils from different varieties of cardamom to have qualitatively the same composition, but variations in the proportions of individual components are evident.

Allied drugs

The long wild native cardamoms of Sri Lanka (Fig. 22.15C) are derived from E. cardamomum var. major Thwaites. They are much more elongated than the official variety, sometimes attaining a length of about 4 cm. The pericarps are dark brown and coarsely striated. The oil distilled from them is used in liqueurs.

‘Amomum’, of the Indian Pharmaceutical Codex, consists of the ripe or nearly ripe seeds of Amomum aromaticum or A. subulatum. The former, obtained from Bengal and Assam, is known as Bengal Cardamom; the latter, obtained from Nepal, Bengal, Sikkim and Assam, as Nepal or Greater Cardamom.

No other similar drugs, unless we include grains of paradise (see below), are imported in any quantity or with any regularity; the following is a list of allied species the seeds of which somewhat resemble those of the true cardamom: A. cardamomum, the round or cluster cardamom of Siam and Java; A. xanthioides, the bastard or wild Siamese cardamom; A. maximum, a Javanese plant; Aframomum korarima, the Korarima or Abyssinian cardamom; A. mala, the East African cardamom; A. hanburii and A. daniellii, Cameroon cardamoms; A. angustifolium, Madagascar cardamom; Costus speciosus, Chinese cardamom. The antiplasmodial activity of A. zambesiacum seeds has been investigated and five new labdane diterpenoids and five known ones isolated (M. Kenmogne et al., Phytochemistry, 2006, 67, 433).

Uses

The principal uses of cardamom are as a flavouring agent in curries and cake. Large quantities are used in Scandinavia and Germany and, with a large proportion of Asiatics in the population, consumption has increased in Britain. Some is used in the manufacture of liqueurs and a relatively small amount in pharmacy, chiefly in the form of Compound Tincture of Cardamom.

Biological activities demonstrated for cardamom include antimicrobial, anti-inflammatory, analgesic, antispasmodic and, recently, gastroprotective (A. Jamal et al., J. Ethnopharmacol., 2006, 103, 149).

History

Owing to the large number of similar composite plants, it has proved impossible to trace the drug in classical writings. The double variety was certainly known in the eighteenth century.

Collection

The flowers are collected in dry weather and carefully dried. The crop is often damaged by wet weather and the discoloured flowers then obtained fetch a much lower price than those having a good colour.

Characters

Each dried flower-head (Fig. 22.16A) is hemispherical and about 12–20 mm in diameter (the BP imposes a 3% limit on small or blemished heads). The florets are of a white to pale buff colour, the outer ones hiding the involucre of bracts. A few hermaphrodite, tubular florets are usually found near the apex of the solid receptacle (see Fig. 22.16B). A transition between the typical tubular florets and typical ligulate ones is often seen. The ligulate florets show three teeth (or occasionally two), the centre one being most developed. There are four principal veins. The corolla is contracted near its base into a tube from which a bifid style projects. The ovary is inferior and devoid of pappus. Each floret arises in the axil of a thin membranous bract or palea which has a blunt apex. At the base of the receptacle is an involucre consisting of two or three rows of oblong bracts which have membranous margins.

Fig. 22.16 A, Cultivated Roman chamomile; B, the same cut longitudinally; C, German chamomile; D, a ligulate floret of same; E, German chamomile cut longitudinally. 1, Tubular floret; 2, ligulate floret; 3, palea; 4, receptacle; 5, bract of involucre. (B after Greenish, remainder after Gilg.)

Chamomiles have a strong, aromatic odour and a bitter taste. The BP/EP includes a TLC test for identity and requires the drug to contain not less than 0.7% of volatile oil and not more than 10.0% water.

Constituents

Chamomiles contain 0.4–1.0% of volatile oil which is blue when freshly distilled owing to the presence of azulene. Other components of the oil are n-butyl angelate (principal), isoamyl angelate, 3-phenylpropyl isobutyrate, tridecanal, pentadecanal and terpenes. Chamomiles also contain sesquiterpene lactones of the germacranolide type, hydroperoxides, dihydroxycinnamic acid and apigenin (a trihydroxy flavone) and luteolin both free and as glucosides. (For the isolation of other constituents see A. Carnat et al., Fitoterapia, 2004, 75, 32.

Uses

Considerable quantities of chamomiles are used in domestic medicine in the form of an infusion (for dyspepsia, etc.) or poultice or in shampoo powders. For the production of volatile oil, the entire aerial parts are usually used.

Constituents

The flower-heads are required to contain not less than 0.4% of a blue volatile oil; this consists mainly of the sesquiterpenes α-bisabolol, chamazulene and farnesene. Chamazulene itself does not occur in the plant but is formed from a sesquiterpene lactone (matricin) during steam distillation.

Flavones and coumarins (e.g. herniarin) are present and the dried ligulate florets contain 7–9% of apigenin glucosides (the 7-glucoside and a mixture of acetates as determined by ¹³C-NMR analysis) and 0.3–0.5% free apigenin, which may arise by post-harvest hydrolysis of the glucosides. In this respect, V. Švehlíková et al. (Phytochemistry, 2004, 65, 2323) have studied the isolation, identification and stability of apigenin-7-O-glucoside in the white florets.A number of chemotypes depending on the proportions of bisabolol, bisabolol oxides and farnesene in the oil have been described. Most Turkish varieties of M. chamomilla yield yellow oils containing no chamazulene; 2n and 4n races have been studied for their respective coumarin variations (A. Pastirová et al., Pharm. Biol., 2005, 43, 205). For an article listing the many known constituents of matricaria flowers see A. Ahmad and L. N. Nisra, Int. J. Pharmacognosy, 1997, 35, 121.

Uses

Matricaria flowers are mainly used on the Continent of Europe and in the USA for their anti-inflammatory and spasmolytic properties. The ulcer-protective properties of German chamomile have been ascribed to bisabolol-type constituents, on which considerable pharmacological work has been reported. Four optically active isomers of bisabolol are possible; extracts for pharmaceutical use should be prepared only from clearly defined types containing the active constituents.

Allied drug

Tanacetum parthenium (L.) Schultz-Bip.; Chrysanthemum parthenium (L.) Bernh., or feverfew flowers may be single or double. The receptacle is flatter than that of the Roman chamomile and may or may not bear paleae. If the latter are present, they are acute and less membranous than those of the chamomile. The whole flowering tops are usually sold. Feverfew herb yields 0.07–0.4% of volatile oil. It is used in herbal medicine; for details concerning its content of sesquiterpene lactones see Chapter 24.

Characters

The flowers occur in characteristically dense terminal corymbs about 3–5 cm in diameter and composed of capitula 3–5 cm in diameter. Each capitulum possesses an involucre of bracts, usually with five white to reddish ligulate ray florets, and 3–20 tubular disk florets. The fruits are achenes. The powdered material contains numerous elements, not only from the flower but also from stems and leaves. These include the typical Compositae pollen grains, leaf epidermis with anomocytic stomata and glandular and clothing trichomes again typical of the Compositae. Fuller details are given in the BP and EP.

Constituents

The pharmacopoeia requires an essential oil content of not less than 0.2% and not less than 0.002% of proazulenes calculated as chamazulene (Fig. 22.17). The tetraploid form of the plant (A. millifolium L., ssp. collina Becker) appears the most suitable as it produces considerable chamazulene as a component of the oil whereas the widespread hexaploid species (A. millefolium L., ssp. millefolium) lacks this guaianolide sesquiterpene. Germacranolide- and eudesmanolide-type sesquiterpenes are also constituents of the oil together with caryophyllene, sabinene, α- and β-pinene, borneol, bornyl acetate, camphor and small quantities of thujone. The proazulenes are determined by measurement of the absorbance (608 nm) of the oil (in xylene) obtained by distillation from the herb.

Fig. 22.17 Constituents of matricaria flowers.

Other isolates from yarrow include sesquiterpene lactones (achillin, achillicin, etc.), flavonoids (apigenin, luteolin, quercetin and their 7-O-glycosides), alkaloids (betonicine, stachydrine, trigonelline) and various acetylenes, coumarins, triterpenes, sterols and plant acids.

V. K. Agnihotri et al. (Planta Med., 2005, 71, 280) studied plants from two different high-altitude (1600 m) populations propagated under uniform environmental conditions at a lower altitude (300 m); the populations represented two ecotypes, a 1:8-cineole type and a borneol type, which differed in oil content and in composition of mono- and sesqui-terpenes.

Uses

Yarrow is used, as is chamomile and matricaria, to treat various skin conditions and digestive disorders. Its pharmacological actions can arise from various groups of compounds—anti-inflammatory (chamazulene and prochamazulenes, apigenin, salicyclic acid), haemostatic (betonicine), spasmolytic (flavonoids).

History

Products of the myrrh type were well known to the ancients under the names of bola, bal or bol. The drug is still known to the Indian traders as ‘heerabol’, while the Somalis call it ‘mulmul’ or ‘ogo’. The name ‘myrrh’ is probably derived from the Arabic and Hebrew word mur, which means bitter. Many references occur in the Old Testament, but the product was apparently that derived from C. erthyaea var. glabrescens, which is known to the Somalis as ‘habbak hadi’, and commercially as perfumed bdellium or bissabol.

Guban myrrh, which is produced from the trees of the Somali coast area known as the Guban, is rather oily and is regarded as inferior to the more powdery ‘ogo’ produced further inland.

Collection

Almost all members of the Burseraceae possess in the phloem oleoresin canals, which are formed schizogenously and may afterwards unite with one another to form schizolysigenous cavities. This occurs in the species Commiphora. Much of the secretion is obtained by spontaneous exudation from the cracks and fissures which commonly form in the bark, and some is obtained from incisions made by the Somalis. The yellowish-white, viscous fluid soon hardens in the great heat to reddish-brown masses, which are collected by the Somalis. As bdelliums and gums are collected at the same time, these frequently find their way into the drug and have subsequently to be picked out.

Characters

Myrrh occurs in somewhat irregular tears or masses weighing up to about 250 g. The surface is reddish-brown or reddish-yellow in colour and powdery. The drug fractures and powders readily, the freshly exposed surface being of a rich brown colour and oily. Whitish marks are sometimes seen and thin splinters are translucent. Myrrh has an aromatic odour and an aromatic, bitter and acrid taste.

Myrrh forms a yellowish emulsion when triturated with water. When extracted with alcohol (90%), as in the preparation of Tincture of Myrrh, a whitish mass of gum and impurities remains. The BP alcohol-insoluble matter should not exceed 70%. Lump myrrh usually yields not more than 5% of ash, but the commercial powdered drug frequently yields more. It may be distinguished from perfumed bdellium and similar products by allowing an ethereal extract of the drug to evaporate to dryness and passing the vapour of bromine over the resinous film produced. A violet colour is given by genuine myrrh but not by bdellium. TLC and visualization with ultraviolet light at 365 nm is used by the BP as an identification test and also to establish the absence of C. mukul, an inferior bdellium product.

Constituents

Myrrh contains 7–17% of volatile oil, 25–40% of resin, 57–61% of ‘gum’ and some 3–4% of impurities.

The volatile oil contains terpenes, sesquiterpenes, esters, cuminic aldehyde and eugenol. The sesquiterpene fraction (Fig. 22.18) contains furanosesquiterpenes including furanogermacranes, furanoguaianes and furanoeudesmanes (N. Zhu et al., J. Nat. Prod., 2001, 64, 1460). Furaneudesma-1,3-diene and curzarene have morphine-like properties and act on the CNS opioid receptors; furanodiene-6-one and methoxy furanoguaia-9-ene-8-one show antibacterial and antifungal activity against standard strains of pathogenic species (P. Dolara et al., Nature, 1996, 379, 29; Planta Medica, 2000, 66, 356). The oil, which is distilled outside the countries of origin, readily resinifies and then gives a violet colour with bromine.

Fig. 22.18 Constituents of myrrh.

The chemistry of the resins is complex and not fully elucidated. The larger ether-soluble portion contains α-, β- and γ-commiphoric acids, the esters of another resin acid and two phenolic resins. The smaller ether-insoluble fraction contains α- and β-heerabomyrrholic acids. The crude alcohol-insoluble matter (‘gum’) contains about 18% of protein and 64% of carbohydrate containing galactose, arabinose and glucuronic acid. This gum is associated with an oxidase enzyme.

Allied drugs

Four different varieties of ‘bdellium’ were recognized by Holmes. Of these, perfumed or scented bdellium or bissabol is probably derived from C. erythaea var. glabrescens. It resembles soft myrrh in appearance but is easily distinguished from it by the more aromatic odour and by the fact that it does not give a violet colour with the bromine test. Hotai bdellium or gum hotai is opaque and odourless; it contains a saponin and is used for washing the hair. The resin of C. confusa collected in Kenya contains dammarane triterpenoids, as does C. kua (L. O. A. Manguro et al., Chem. Pharm. Bull., 2003, 51, 479, 483).

Uses

Myrrh is used in incense and perfumes. Like many other resins, it has local stimulant and antiseptic properties. It is chiefly employed in medicine in the form of a mouth-wash or gargle for its astringent effect on mucous membranes. A number of its traditional and historic uses have received experimental support.

Collection and preparation

The collection of asafoetida involves removal of the stem and the cutting of successive slices from the vertical rootstock. After each slice is removed, oleo-gum-resin exudes and, when sufficiently hardened, is collected. The product is packed in tin-lined cases for export.

Characters

Asafoetida occurs in two principal forms.

Tears. These are rounded or flattened and about 5–30 mm diameter. They are greyish-white, dull yellow or reddish-brown in colour, some specimens acquiring the latter colour with age, while others remain greyish or yellowish.

Mass. This consists of similar tears to those described above agglutinated into masses and usually mixed with fruits, fragments of root, earth and other impurities. Mass asafoetida is the commonest commercial form.

Asafoetida has a strong, alliaceous odour and a bitter, acrid and alliaceous taste. It should yield not more than 50% of matter insoluble in alcohol (90%) and not more than 15% of ash.

Constituents

Asafoetida consists of volatile oil, resin, gum and impurities. The oil has a particularly evil smell and contains sulphur compounds of the formulae C₇H₁₄S₂, C₁₆H₂₀S₂, C₈H₁₆S₂, C₁₀H₁₈S₂, C₇H₁₄S₃, and C₈H₁₆S₃; some of these show pesticidal activity. The flavour is largely due to R-2-butyl-1-propenyl disulphide (a mixture of E and Z isomers), 1-(1-methylthiopropenyl)-1-propenyl disulphide and 2-butyl-3-methylthioallyl disulphide (both as mixtures of diastereoisomers). The drug also contains a complex mixture of sesquiterpene umbelliferyl ethers mostly with a monocyclic or bicyclic terpenoid moiety; more recently (G. Appendino et al., Phytochemistry, 1994, 35, 183) three new sesquiterpene coumarin ethers have been isolated. Also present are asaresinol ferulate and free ferulic acid. For selected formulae see Fig. 22.19. The drug contains no free umbelliferone (distinction from galbanum). However, on boiling it with hydrochloric acid and filtering into ammonia, a blue fluorescence is produced owing to the formation of umbelliferone. Ferulic acid is closely related to umbellic acid and umbelliferone (both of which occur in galbanum).

Fig. 22.19 Constituents of asafoetida.

Allied drugs

Galbanum and ammoniacum are oleo-gum-resins obtained, respectively, from Ferula galbaniflua and Dorema ammoniacum. Galbanum contains, besides umbelliferone, a number of umbelliferone ethers; also gum and up to 30% of volatile oil containing numerous mono- and sesquiterpenes, azulenes and sulphur-containing esters. Ammoniacum, listed in the BHP, contains free salicylic acid but no umbelliferone. The major phenolic constituent is ammoresinol; Appendino et al. (Helv. Chim. Acta, 1991, 74, 495) isolated an epimeric mixture of prenylated chromandiones termed ammodoremin. The volatile oil (c. 0.5%) contains various terpenoids with ferulene as the major component. The demonstration of the broad spectrum and antimicrobial activity of ammoniacum has supported its traditional use for chest infections (M. Rajani et al., Pharm. Biol., 2002, 40, 534).

Uses

Asafoetida is included in the BHP (Vol. 1, 1990) and is employed for the carminative and expectorant properties of the volatile oil fraction. It is an ingredient of certain sauces.

Characters

The colophony described in the BP/EP occurs in translucent glassy masses of a pale yellow or amber colour. It is brittle and easily powdered. It fuses gradually at about 100°C, and at a higher temperature burns with a smoky flame, leaving not more than about 0.1% of ash. Colophony is insoluble in water but soluble in alcohol, ether, benzene and carbon disulphide.

Chemical tests

Constituents

Colophony contains resin acids (about 90%), neutral inert substances formerly known as resenes and esters of fatty acids.The exact composition varies with biological source, preparation, age and method of storage.

The resin acids are isomeric diterpene acids. It will be noted that colophony has a high acid value of 150–180.

Before distillation the resin contains large amounts of (+)- and (−)-pimaric acids. During distillation the (+)-pimaric acid is stable but the (−)-pimaric acid undergoes isomeric change into abietic acid, the major constituent of the commercial resin (see formula, p. 264). On heating at 300°C abietic acid undergoes further molecular rearrangement to produce some neo-abietic acid. The commercial ‘abietic acid’ is prepared by digesting colophony with weak alcohol.

The abietane acids have been considerably investigated over recent years; they are obtained chiefly from colophony but are also present in other conifers of the Araucariaceae, Cupressaceae, Pinaceae and Podocarpaceae. Their activities are mainly antimicrobial, antiulcer and cardiovascular; some have filmogenic, surfactant and antifeedant properties.

Uses

The amount of colophony used in pharmacy for the preparation of zinc oxide and other adhesive plasters, ointments, etc., is relatively small. Much rosin is artificially modified by hydrogenation or polymerization; products involving its use include paper size, adhesives, printing inks, rubber, linoleum, thermoplastic floor tiles and surface coatings.