The genus Citrus includes a number of well-known medicinal and food plants: orange, lemon, orange, tangerine, bergamot, grapefruit, etc.
These types of citrus fruits are evergreen, low trees. In some species, the branches are equipped with spines. The leaves are leathery, shiny, dark green, oval in shape with a pointed apex, traditionally entire, in some species the petioles are winged. Flowers solitary or several in leaf axils, white, regular, separate-petaled; calyx 4-5-toothed, small, corolla traditionally of 4-5 petals, many stamens, ovary upper multi-celled. All parts of the plant are fragrant and contain schizolysigenic spherical or oval receptacles immersed in the parenchyma.
The fruit is berry-shaped, unique in other families, received the specific name “hesperidium” (hespiridium). The outer part within the fruit, or peel, is thick, soft, tuberculate on the outside, colored, called flavedo; the inside is white, odorless and tasteless – albedo. The pulp of the fruit is divided into 8-12 lobules (corresponding to the number of nests of the tie). The lobules are filled with sticky “juice sacs” – outgrowths of the inner walls of the ovary nests. Between the juice sacs in the slice is 1-3 seeds. There are no essential oil receptacles in the pulp of the fruit, they are concentrated in many in the outer layer of the peel (flavedo) and when pressed on the surface of the fruit with a fingernail, a drop of oil comes out.
Southeast Asia is considered the birthplace of citrus fruits, but the species used have changed so much over several millennia that their wild relatives cannot be found. The centers of ancient culture are China, probably also the countries of Indochina and India, from where the culture spread to neighboring countries. Some, probably fragrant, but inedible species were known in Mesopotamia before the new era. Some species were brought to Greece from India and Persia (Iran) during the campaign of Alexander the Great. But the cultivation of citrus fruits was most widespread in the Middle Ages thanks to the Arabs. They introduced plants into cultivation in the states of the Mediterranean Sea – along the coast of Africa, in Sicily and Spain, and here they introduced Europeans to citrus fruits called “naryanj” and “limun”. However, citrus became more widely interested in Europe only after the travels of Vasco de Gama, who brought seeds that were bred in greenhouses. In the XVI century. Citrus culture has penetrated into Central and South America.
At present, citrus plantations occupy vast areas in all states with a subtropical climate, where they grow better than in the tropics.
In medicine, from citrus – sources of natural oils, the following are used:
1. Pomeranian – Citrus aurantium L. subspecies amara Engl, syn. C. bigaradia Risso. The orange tree is distinguished by its long, sharp spines. The fruit is spherical, 6-7 cm in diameter, orange-red, bitter in taste, inedible.
Orange peel contains 1-3% essential oil, 1-2.5% bitter glycoside – aurantiamarin and flavanone glycosides – hesperidin and isohesperidin, belonging to the group of vitamins P. The essential oil consists of 90-95% limonene; in addition, it contains terpineol, linalool, citronellol and other substances.
The essential oil is obtained from the freshly peeled peel by squeezing under pressure, or whole fruits are placed in rotating cylinders with serrated walls; the gears break the receptacles and the oil flows out. The essential oil is known as Oleum Petitgrain.
From fresh unripe fruits, collected together with small twigs, an essential oil (up to 0.7%) is obtained by steam distillation, known as Oleum Petitgrain (in French petit – small, grain – grains). Used in ointments, used in perfumery. It has a different aroma than the oil obtained from the orange peel.
In small volumes, essential oil is also obtained from orange leaves, where it is localized in the mesophyll of the leaf in receptacles (within 0.3%). The oil is called Oleum Aurantii foliorum and also differs in smell.
From fresh orange flowers, containing within 1% essential oil, it is obtained by steam distillation or enfleurage. It is called Oleum Aurantii florum. Oleum Naphae Oleum Neroli. This oil has a completely different than all the previously mentioned essential oils, a very pleasant smell: it contains limonene and all kinds of esters of linalool and geraniol (up to 40%) and a non-cordial amount (0.4-1%) of anthranilic methyl ester (o-amidobenzoic) acid, which gives the oil a delicate aroma. The oil is used in ointments, used in perfumery.
2. Orange – Citrus sinensis Risso (Citrus aurantium L. subspecies dilcis Engl.). Orange peel and its essential oil are included in the British Pharmaceutical Code. The essential oil contains within 90% limonene. It is used for aromatization of medicines and foodstuff.
3 . Bergamot – Citrus bergamia Risso. Tree without thorns. The fruit is pear-shaped, 6-7.5 cm long, 5.5-6.5 cm in diameter (at the base), golden yellow with a greenish tinge. The peel contains 1-3% essential oil, hesperidin and furocoumarins and bergaptol, bergapten. Essential oil (Oleum Bergamottae) contains limonene and other terpenes, but linadyl acetate (30-45%) and free linalool provide a specific pleasant aroma. Bergamot oil is used for fragrance ointments and in perfumery.
4. Lemon – Citrus limon Burm. (syn. Citrus limonium Risso). The tree has short spines, the petiole of the leaves is not winged, the edge of the leaf is finely serrated; calyx 5-toothed, corolla 4-8-lobed. The fruit is oval in shape, at the apex and at the base it is elongated into a nipple 6-9 cm long or more, 4-6 cm in diameter, light yellow. The peel contains within 0.6% essential oil, flavanone glycosides hesparidin and erythrocitrin and furocoumarins. The essential oil is extracted in the same way as orange oil, since during steam distillation it loses its natural smell to a large extent. The essential oil (Oleum Citri) contains within 95% terpenes, mainly limonene, about 3% citral, 1% geranyl acetate and some citronellol; Citral is the carrier of the lemon scent.
The plant contains monocyclic terpenes.
PLANTS CONTAINING MONOCYCLIC TERPENE
Monocyclic terpenes are derivatives of methylisopropylcyclohexane with two (or one) double bonds. Double bonds can be both in the ring (terpenes, a-phellandrene) or one of them is in the isopropyl group (limonene) or at C 1 -C 7 ) b-phellandrene).
Of the oxygen derivatives, the most common are: alcohols – terpineol, menthol, ketones – menthone, piperitone, carvone, oxides – cineol.
Some monocyclic terpenes are often present in essential oils together with aliphatic terpenes (eg essential oils of many citrus fruits) or accompany bicyclic monoterpenes and sesquiterpenes (see below). For these reasons, the division of essential oil plants into groups of terpenes is somewhat arbitrary.
PLANTS CONTAINING ESSENTIAL OILS
Essential oils are natural aromatic substances that are highly volatile and cause the specific smell of plants. For this reason, also due to their “oily” consistency and “greasy” stain on paper, which soon disappears, they received such a peculiar name.
Essential oils are not individual substances. These are complex mixtures of organic substances, the composition and number of which are different for each type of essential oil plants and can serve as a chemotaxonomic feature. The main group of substances that make up the essential oils of many plants are terpenes (more precisely, monoterpenes) and seseviterpenes, i.e., substances with an isoprenoid structure. However, in the essential oils of a number of plants, aromatic compounds may predominate, as well as numerous substances of the aliphatic series. There are plants with sulfur and nitrogen compounds in essential oils.
Essential oils in plants are mostly in a free state. However, some plants contain them in the form of glycosides and are released during enzymatic cleavage. Essential oils are formed in all parts of plants, but quantitatively they accumulate in them traditionally unequally.
They can be in a plant organism in a diffuse diffuse state (ie, emulsified or dissolved in cells) or accumulate, localize in special anatomical and morphological formations that are easily detected under a microscope. These excretory formations can be exogenous and endogenous.
Exogenous formations develop in the epidermal tissue and are:
– glandular “spots” – small-drop accumulations of essential oils immediately under the cuticle of the epidermis;
– glandular hairs – cylindrical epidermal outgrowths, consisting of a unicellular or multicellular pedicle and a head with cells that secrete essential oil;
– glands – epidermal outgrowths that have received the most
the highest specialization in the extraction and accumulation of essential oils. They have a different structure and can serve as a systematic feature. For example, in yasnotkovye (labial) 8 excretory cells are arranged in a rosette on a short stalk; in aster (composite) glandular cells have a vertical arrangement – 2 in 4 rows, etc.
Endogenous formations develop in parenchymal tissues and are:
– secretory cells – single (for example, in the air parenchyma of calamus rhizome) or form layers of such cells (for example, in valerian roots);
– receptacles – rounded cavities formed in the mesophyll of the leaf, peel of citrus fruits, in the bark and wood of a number of plants and filled with essential oil;
– tubules and passages – strongly elongated excretory formations found in the fruits of umbellate, bark and wood of a number of plants.
Essential oils accumulate in plants in all possible quantities: from hundredths and thousandths of a percent (for example, in violet flowers – 0.004%) to 20% or more (for example, in flower buds of carnations – up to 23%).
Essential oils are obtained: 1) by steam distillation; 2) extraction with some extractants; 3) enfleurage; 4) mechanically.
Steam distillation is the most common method. It is carried out in installations consisting of a double-jacketed still (in which steam circulates to prevent the still from cooling), a condenser and a receiver. Steam is fed into the cube loaded with raw materials from below through a perforated coil, entraining the essential oil. A mixture of cooled vapors of water and essential oil enters the receiver, where the mixture separates and excess water is removed through a tube at the bottom of the receiver (if oil is lighter than water) or through a drain tube at the top (if oil is heavier than water).
The extraction of essential oils from raw materials is carried out with volatile organic solvents in Soxhlet-type apparatuses or in column apparatuses. Subsequently, the raw material is lifted by the screw from the bottom up, and the extractant enters towards it. After distillation of the solvent, the residue is either pure essential oil or its mixture with other extracted substances (resins, waxes, etc.); in the latter case, additional cleaning is required.
Enfleurage is based on the fact that essential oil from raw materials (mainly from flowers) is absorbed by sorbents (solid fats, activated carbon, etc.) in special frame installations.
The mechanical method is used to extract essential oils from citrus fruits by pressing or scraping.
Although essential oils are very common in the plant world, their role for the plant organism and the reasons for their formation have not yet been reliably established. It was assumed that essential oils serve to protect plants from diseases and pests, to attract the smell of insects, which contributes to the pollination of flowers, to protect plants from excessive heating during the day and hypothermia at night, etc. Currently, most scientists believe that essential oils (or rather, their components) are actively involved in the metabolic processes of plant organisms.
Essential oils find a wide and varied application for medicinal, cosmetic, food (spices) and other chains.
Essential oils are classified according to the substances that make up their bulk, or substances that determine their medicinal and industrial value. There are the following groups (and subgroups) of components of essential oils:
Monoterpenes (terpenes), including:
1. Acyclic terpenes.
2. Monocyclic terpenes.
3. Bicyclic terpenes.
Sesquiterpenes, including:
1. Acyclic sesquiterpenes.
2. Cyclic sesquiterpenes.
Aromatic and phenolic compounds.
Sulfur and nitrogen-containing compounds.
The listed compounds, especially terpenoids, in essential oils can occur in the form of numerous oxygen derivatives: alcohols, aldehydes, ketones, phenols, acids, esters, lactones, oxides, quinones. The number of terpenoids also increases due to the tendency of many of these compounds to various forms of isomerism (optical, geometric, etc.).