Linseed Oil

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Chapter: Pharmacognosy and Phytochemistry : Drugs Containing Lipids

Linseed is the dried, ripe seed of Linum usitatissimum Linn. Linseed oil is obtained by expression of linseeds, belonging to family Linaceae.


LINSEED OIL

 

 

Synonyms

 

Flax seed, alsi (Hindi).

 

Biological Source

 

Linseed is the dried, ripe seed of Linum usitatissimum Linn. Linseed oil is obtained by expression of linseeds, belonging to family Linaceae.

 

Geographical Source

 

Linseed is cultivated in many sub-tropical countries such as South America, India, United States, Canada, England, Russia, Greece, Italy, Spain, and Algeria.

 

Collection

 

Linseed in an erect annual herb, 60–120 cm high with sky-blue flowers, and a globular capsule. The plant is cultivated for its seeds and fibre (flax). A moderate rainfall is best suited for its growth. It grows in almost all types of soils where sufficient moisture is available, but thrives best in heavy soils with high moisture retaining capacity. As a mixed crop it is sown either on the margins of fields or in rows alternating with the other crop. Nitrogenous fertilizers yield better crop. The crop is harvested in Feb-ruary and March before the capsules are dried. Plants are cut close to the ground, dried in the field, and threshed to separate seeds.

 

Morphology of Seeds

 

The seeds are oval, flattened, elongated, 4–6 mm long, and 2–3 mm wide. Testa is glossy, smooth, reddish-brown with minutely pitted surface. Seeds are rounded at one end. The other end is obliquely pointed where the hilum and micropyle are present in a slight depression. Raphe is present along one edge. Endosperm is narrow and encircles the embryo. It consists of two thick flattened, plano-convex cotyledons, and a radicle. The seeds art odourless but possess an oily and mucilaginous taste.

 

Microscopical Characters

 

Under microscope the testa shows a mucilage-containing outer epidermis; one or two layers of collenchyma or ‘round cells’; a single layer of sclerenchyma; the hyaline layers or ‘cross-cells’ composed in the ripe seed of oblit-erated parenchymatous cells; and an innermost layer of pigment ceils. The outer epidermis is composed of cells, rectangular or five-sided in surface view, which swell up in water and become mucilaginous. The outer cell walls, when swollen in water, show an outer solid stratified layer. The radial layers or ‘round cells’ are cylindrical in shape and show distinct triangular intercellular air spaces. The sclerenchymatous layer is composed of elongated cells, up to 250 μm in length, with lignified pitted walls. The hyaline layers are attached to portions of the sclerenchymatous layer in the powdered drug. The pigment layer is composed of cells with thickened pitted walls and containing amorphous reddish-brown contents. The cells of the endosperm and cotyledons are polygonal with thickened walls, and contain numerous aleurone grains and globules of fixed oil.

 


 

Preparation

 

The dried seeds are crushed in rollers, moistened and heated to 80–90°C in steam to soften the seed tissues. They are then pressed through hot hydraulic press at a high pressure. The oil so obtained is treated with alkali to separate free fatty acids and bleached with fuller’s earth or charcoal. On cooling the oil waxy substances are removed.

 

Linseed oil is a yellowish liquid, with a peculiar odour and bland taste. On exposure to air it gradually thickens, becomes darker and acquires a more pronounced odour and taste. On drying it forms a hard varnish. It has a high iodine value (~170) which indicates the presence of excess amount of glycerides of unsaturated fatty acids. The oil is slightly soluble in alcohol, miscible with chloroform, ether, petroleum ether, carbon disulphide, and terpentine oil. It has density 0.925–0.935, viscosity 1.47, congealing point ~20°C, saponification number 187–195, refractive index 1.47–1.48, and unsaponifiable matters not over 1.5%. A water-soluble resinous matter with antioxidant properties has been isolated from the oil.

 


 

Chemical Constituents

 

Linseed contains fixed oil (30–40%), mucilage (6–10%), protein (25%) (linin and colinin), small amount of enzyme lipase, and linamarin which is a cyanogenetic glycoside. The carbohydrates present are sucrose, raffinose, cellulose, and mucilage. Linamarin is a glucose either of acetone cyanohydrin and is identical to phaseolunatin. Unripe seeds contain starch which is converted to mucilage on ripening the seeds. The mucilage can be fractionated into a neutral fraction a remified, arabinoxylan composed of D-xylose, -arabinose,  -glucose and  -galactose; and an acidic frac tion mainly composed of L-rhamnose and D-galactose. Mucilage swells with water and forms red colour with ruthenium red. Linamarin on hydrolysis yields acetone, hydrocyanic acid, and glucose. The other constituents are phytin, lecithin, wax, resin, pigments, malic acid, cyanogenic glycosides linustatin neolinustatin, and secoisolariciresinol and phenylpropanoid glucoside linusitamarin.

 

On hydrolysis Linseed oil produces unsaturated acids like linolenic acid (30–50%), linoleic acid (23–24%), oleic acid (10–18%) together with saturated acids-myristic, stearic, and palmitic (5–11%).

 

Uses

 

Linseed is used as demulcent and in form of poultices for gouty and rheumatic swellings. Internally it is used for gonorrhoea and irritation of the genito-urinary system. Linseed oil has emollient, expectorant, diuretic, demulcent, and laxative properties and is utilized externally in lotions and liniments. Nonstaining iodine ointment soap, linoleum, greases, polishes, polymers, varnishes, paints, putty, oil cloths, printing inks, artificial rubber, tracing cloth, tanning and enamelling leather, etc. are also prepared from Linseed oil.

 

The mucilaginous infusion is used internally as a demulcent in colds, coughs, bronchial affections, inflammation of the urinary tract, gonorrhoea, and diarrhoea.

 

Adulterants

 

When market price is high, Linseed oil is adulterated with vegetable oils, such as rape, cottonseed, soyabean, sunflower, safflower and candlenut, as well as with rosin and mineral and fish oils. Boiled Linseed oil is more frequently adulterated than raw oil.

 

Admixture of rape and mustard oils may be detected by the presence of erucic acid; the adulterants lower the saponification value. Fish oil may be detected by the odour produced on heating and by melting points of ether insoluble bromides. Rosin and mineral oils increase the proportion of unsaponifiable matter.

 

Marketed Products

 

It is one of the ingredients of the preparations known as Canisep and Scavon (Himalaya Drug Company).

 

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