Neem Biology and Chemistry

The Neem Tree

The Neem tree (Azadirachta indica) grows in tropical and sub tropical countries such as India, Africa and Australia. It belongs to the family Meliaccae, and is a cousin of the Chinaberry. It may reach up to 15m tall under ideal conditions, and is reported to live for up to 200 years. It has a short straight furrowed trunk, dark brown or grey in colour, with dense rounded crowns of pinnate leaves. It can tolerate temperatures of up to 120 deg. C, and rainfall as little as 45cm. It must have well drained soil, and will respond well to organic fertilisers - although being hardy, it can still grow luxuriantly in marginal and leached soils, up to an elevation of 1500m.

Flowering is between February and May, with profuse clusters of small white flowers having a very sweet jasmine or honey-like scent. The flowers provide a good source of nectar for bees. Following on from flowering, the fruit are green drupes, turning golden yellow on ripening, which occurs during June, July and August in India. The fruits (or drupes) are about 1.5 cm long, edible, and loved by African children.

The tree will normally begin bearing fruit after 3 to 5 years, and produce about 50kg annually when mature. The kernels of these fruits yield about 45% neem oil. The bark yields tannin and amber coloured gum, used as a dye in textiles as well as traditional medicinal usage.

The Neem tree is related to mahogany, and is used locally for furniture and building purposes. The inherent properties of Neem make it resistant to termites. In India, it has not tended to be a 'plantation' species, and is most often seen along the roadside and in gardens as a 'shade' tree. Local tradition dictates that Neem trees should be planted near the home to ensure good health to those that live there.

Constituents of Neem

Plants are made up of thousands of chemicals, and Neem is no different in this respect. However, scientists are particularly interested in one family of chemicals particular to Neem, and responsible for its amazing properties. These are the 'tetranortriterpenoids' or more specifically 'liminoids' - similar to steroids. About 40 of these chemicals act together, producing a synergistic or enhanced affect. The most active and well studied of these is 'Azadirachtin'.

As scientists continue to fully unravel the mystery of Neem, they have discovered that although Neem terpenoids are present in almost all parts of the plant, the site, synthesis and accumulation of these chemicals occurs in the secretory cells. These cells are most abundant in the seed kernels, from which the oil is harvested. The following are the most abundant and well studied chemicals in the Neem Tree:

• Nimbin-  anti-inflammatory, anti-pyretic, antihistamine, anti-fungal
• Nimbidin- anti-bacterial, anti-ulcer, analgesic, anti-arrythmic, anti-fungal
• Nimbidol- anti-tubercular, anti-protozoan, anti-pyretic
• Gedunin- vasodilator, anti-malaria, anti-fungal
• Sodium Nimbinate- diuretic, spermicidal, anti-arthritic
• Quercetin- anti-protozoal, antioxidant, anti-inflammatory, anti-bacterial
• Salannin- insect repellent
• Azadirachtin- insect repellent, anti-feedant, anti-hormonal 

Major concentrations of the active components are found in the seed and oil, most are also found in the bark and leaf, though in lesser amounts. Extensive research has revealed the many and various beneficial properties they deliver. The oil is also rich in long chain fatty acids. In addition to the active ingredients listed above, analysis reveals many other vital nutrients: fibre, carbohydrates, calcium, at least ten essential amino acids and also carotenoids which are powerful antioxidants.