Cymbopogon Spreng.
There are more than 20 species of fragrant perennial Indian cereals belonging to the genus Cymbopogon, the tribe Andropogoneae. More widely known are citronella, lemongrass, and palmarosa essential oils.
1. Citronella. Orange grass -Cymbopogon nardus L. Rendle. A tall cereal native to the mountains of South India and Sri Lanka. Widely cultivated in India, Indonesia and other islands of Asia and Africa. The essential oil is obtained from the herb by distillation. A large yield of essential oil is given by the leaves, where it is located in long secretory cells.
Essential oil (Oleum Citronellae) contains up to 50% citronellal, citronellol and geraniol and their esters, up to 15% terpenes (camphene, dipentene, limonene) and some sesquiterpenes. The plant is popular in local folk medicine. Insecticide against mosquitoes and moths. The oil is used in the perfumery and cosmetic industry (toothpastes, etc.).
2. Lemongrass – Cymbopogon citratus (DC.) Stapf. It is known only in culture – in the states of tropical and subtropical Asia, Africa and America. In the USSR – an annual culture. Perennial crop yields 4 times a year; the greatest harvest is obtained in the 8-10th year (the plant lives up to 15 years).
The leaves smell of lemon and their essential oil (Oleum Lemongrassae) contains within 85% citral and up to 20% myrcene. The most valuable Indian oil from the Malabar coast. Citral is of great medical importance. Water-alcohol solutions (1:10000) of citral are used in ophthalmic practice for keratitis and conjunctivitis. Citral is used for the synthesis of vitamin A (according to the method of N. A. Preobrazhensky) – to obtain the main link of this vitamin – ionone. The oil is widely used in the food industry.
The local population drinks tea from the leaves as a gastric remedy. For fever, take hot baths with leaves and drink hot tea from the leaves. In tropical Africa (Nigeria), tsetse flies and mosquitoes are repelled by planting lemongrass.
3. Cymbopogon Martini. Palmorosa -Cymbopogon martini Stapf. Distributed in India from Bengal to the borders of Afghanistan and from the subtropical Himalayas to 12 ° N. sh., except for deserts. Cultivated in India, Indochina, Indonesia, Seychelles.
This perennial cereal in culture blooms after 5 months after sowing. Flowering grass is cut to obtain essential oil. Essential oil – Oleum Palmorosae, obtained from Cymbopogon martini Stapf, var. motia, has a rose scent and contains 75-95% geraniol, part of which (3-13%) is esterified. The oil also contains citral, farnesol and some terpenes. Replaces geranium and rose oil.
The plant contains acyclic monoterpenes.
PLANTS CONTAINING ACYCLIC MONOTHERPENES
Acyclic (or aliphatic) monoterpenes are unsaturated fatty compounds with 3 double bonds (for example, myrcene), contained in essential oils mainly in the form of oxygen derivatives – geraniol, linalool, citronellol (alcohols), citronellal, citral (aldehydes), linalyl acetate, geranylisovalerianate (esters, etc.).
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.).