Neem oil is a vegetable oil pressed from the fruits and seeds of the neem (Azadirachta indica), an evergreen tree which is indigenous to the Indian subcontinent and has been introduced to many other areas in the tropics. It is the most important of the commercially available products of neem for organic farming and medicines.
Neem oil varies in color depending on the number of days the seeds are soaked in water; it can be golden yellow, yellowish brown, reddish brown, dark brown, greenish brown, or bright red. It has a rather strong odor that is said to combine the odours of peanut and garlic. It is composed mainly of triglycerides and contains many triterpenoid compounds, which are responsible for the bitter taste. It is hydrophobic in nature; in order to emulsify it in water for application purposes, it is formulated with surfactants.
Azadirachtin is the most well known and studied triterpenoid in neem oil. Nimbin is another triterpenoid which has been credited with some of neem oil's properties as an antiseptic, antifungal, antipyretic and antihistamine. Neem oil also contains several sterols, including campesterol, beta-sitosterol, and stigmasterol.
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The method of processing is likely to affect the composition of the oil, since the methods used, such as pressing (expelling) or solvent extraction or standard cold pressed method are unlikely to remove exactly the same mix of components in the same proportions. The neem oil yield that can be obtained from neem seed kernels also varies widely in literature from 25% to 45%.
The oil can be obtained through pressing (crushing) of the seed kernel both through cold pressing or through a process incorporating temperature controls between 40 °C and 50 °C. Hence, it is also called as cold pressed neem oil.
Neem seed oil can also be obtained by solvent extraction of the neem seed, fruit, oil, cake or kernel. A large industry in India extracts the oil remaining in the seed cake using hexane. This solvent-extracted neem oil is of a lower quality as compared to the standard cold pressed neem oil and is mostly used for soap manufacturing. Neem cake is a by-product obtained in the solvent extraction process for neem oil.
The ingestion of neem oil is potentially toxic and can cause metabolic acidosis, seizures, kidney failure, encephalopathy and severe brain ischemia in infants and young children. Neem oil should not be consumed alone without any other solutions, particularly by pregnant women, women trying to conceive, or children. It can also be associated with allergic contact dermatitis.
Formulations made of neem oil also find wide usage as a biopesticide for organic farming, as it repels a wide variety of pests including the mealy bug, beet armyworm, aphids, the cabbage worm, thrips, whiteflies, mites, fungus gnats, beetles, moth larvae, mushroom flies, leafminers, caterpillars, locust, nematodes and the Japanese beetle. Neem oil is not known to be harmful to mammals, birds, earthworms or some beneficial insects such as butterflies, honeybees and ladybugs (ladybirds in English English) if it is not concentrated directly into their area of habitat or on their food source. It can be used as a household pesticide for ant, bedbug, cockroach, housefly, sand fly, snail, termite and mosquitoes both as repellent and larvicide.
Neem extracts act as a antifeedant and by blocking the action of the insect molting hormone ecdysone. Azadirachtin is the most active of these growth regulators (limonoids), occurring at 0.2–0.4 % in the seeds of the neem tree.
- W. Kraus, "Biologically active ingredients-azadirachtin and other triterpenoids", in: H. Schutterer (Ed.), The Neem Tree Azadirachta indica A. Juss and Other Meliaceous Plants, Weinheim, New York, 1995, p 35-88
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