Case Studies of Neem Processing Projects Assisted by GTZ in Kenya, Dominican Republic, Thailand and Nicaragua (GTZ, 2000, 152 p.) 2. Survey of neem-processing methods (introduction...) 2.1 Home-made products 2.2 Commercial products (introduction...) 2.2.1 Collection systems 2.2.2 Harvesting methods 2.2.3 Processing technology seeds Extraction technologies (introduction...) A) Extraction with alcohol (also called one-step extraction) B) Refined neem extracts - AZADIRACHTIN-ENRICHED EXTRACTS (also called two-step extraction plant) C) Extraction using centrifuges D) Extraction with Supracritical CO2

Case Studies of Neem Processing Projects Assisted by GTZ in Kenya, Dominican Republic, Thailand and Nicaragua (GTZ, 2000, 152 p.)

2. Survey of neem-processing methods

In principle the following product lines can be characterised:

2.1 Home-made products

To prepare a simple extract from 1 kg of crushed neem seed or fruits, these are soaked and stirred in 20 litres of water and left for 5 to 8 hours, preferably during the daytime (Dreyer & Hellpap 1992, Hellpap 1989, Schmutterer 1995). The neem extract can be filtered and directly sprayed on the target crops, preferably in the evening to avoid UV light (which destroys the active ingredients) as long as possible.

This method is also known as the "tea bag method".

There are some examples reported from Thailand, where this method is even used for larger areas of vegetables. Farmers have developed simple technologies, putting 50 kg bags of crushed neem fruits into iron drums and spraying the water extracts on a large scale with motor driven pumps.

The neem remains or marc can be dried and packed or applied to the soil as a soil additive or to control soil insect pests and nematodes.

In addition, the neem seeds or neem cake from oil pressing may be ground to produce powder. This powder can be used to produce water extracts or can be directly applied to the soil or to plants themselves (e.g. funnels of maize).

Neem seeds can also be processed into oil which, mixed with soap (or better, an emulsifier) can be applied by spraying.

2.2 Commercial products

The following steps are required for the commercialisation of neem products:

· Harvest: hand picking (for best quality) or collecting (sweeping up) fruits and kernels which have been depulped by bats and birds

· Cleaning with water/sand

· De-pulping: by hand or modified coffee depulper

· Drying: controlled exposure to sunlight/drying device

· Disinfection with calcium hypochlorite

· Storage in a dry, shady and well ventilated place, preferably at 20 C

· Extraction:

· alcoholic batch extraction (one-step extraction)

· methods for obtaining an azadirachtin-enriched extract: two-step extraction, supercritical CO₂,

· Formulation: increases stability but emulsifiers often also have synergistic or additive effects (e.g. sesame, soya or castor oil, piperonyl butoxide etc.).

2.2.1 Collection systems

The commercialisation of neem products requires an effective and reliable collection system for neem seeds, which does not exist in most countries. It turns out that reliable collection and preparation of neem kernels of good quality for a reasonable price is one of highest hurdles in setting up neem processing in developing countries. On the one hand, in participatory training communities have to be persuaded to collect neem seeds during the one or two local harvesting seasons and to accept neem as an additional cash crop; on the other hand there has to be a commitment on the part of the entrepreneurs to buy a certain amount of the collected seeds frequently, even if they cannot process them all due to marketing problems. Moreover, the kernels may be of inferior quality in the early stages or due to extraordinary weather conditions, e.g. contaminated with fungi (Aspergillus spp.). The entrepreneurs, however, should keep the collectors motivated by continuing to buy at least some of the seeds. It is helpful to intensify the training and pay a premium for better quality.

2.2.2 Harvesting methods

There exist two ways to obtain neem seeds:

· birds and/or bats feed on the pulp of the ripe neem fruits and drop the seeds underneath or near the trees (which happens in some places in Asia and Africa);

or

· the fruits are picked from the tree (in areas where the neem tree has been introduced only recently such as central and south America). The seeds are then collected from the ground.

In the former case the seeds can be collected (swept up) more cheaply but further cleaning from debris is still required, as is depulping sometimes.

There are different harvesting techniques applied in other regions; the best one was developed in Nicaragua.

Pruning takes place during harvesting time, so a good proportion of the seeds can be picked directly from the chopped branches on the ground. Leupolz (1995) found that the average harvesting capacity is 30 kg fruits during 6 working hours (5 kg fruits/h).

During picking of the neem fruits the workers do not differentiate between ripe and unripe fruits for reasons of efficiency. Unripe fruits are stored in the shade at the processing site.

The average harvest in neem plantations is approx. 5 kg fruits/tree.

2.2.3 Processing technology seeds

Neem fruits can be processed in two different ways:

a) Wet processing on a small scale:

The fruit is depulped by hand, by rubbing and squeezing the pulp in water using sieves or hand-driven modified coffee depulpers. Modified coffee depulpers, however, have turned out to cause too much loss (damaged kernels and subsequent fungal infection).

The unripe fruits can be depulped after being stored for 4 - 5 days in the shade. After depulping, the seeds have to be washed in water, dried for 4 - 5 hours in the sun and then moved to the shade, if the sun is strong enough to risk lowering the azadirachtin content of the kernels. The time required for drying depends on the climatic conditions. The seeds should have a moisture content of less than 7%. A higher moisture content will lead to fungal contamination and subsequently to a reduced azadirachtin content.

b) Wet processing in a depulping plant:

Here the fruits are delivered to a processing plant. The process is more or less the same as on a small scale. The fruits are sorted into ripe and unripe ones. The ripe ones are depulped in depulping rollers (cylinders) with a capacity of 300-500 fruits/hour.

The depulped seeds will be either washed manually or by mill electric washing machines to be eventually dried on drying sieves.

Usually the limiting factor for wet processing units is the lack of sites covered by a roof for ripening the unripe fruits and for drying the seeds. A problem encountered by both small-scale and semi-industrial processing is the lack of adequate drying units for the seeds, to avoid fungal contamination and reduce the moisture content.

In arid areas without water the seeds are cleaned by rubbing them in sand.

For storage, the seeds should be disinfected by some means, e.g. calcium hypochlorite, and dried in the sun or by heating devices to achieve a moisture content lower than 7%. The seeds should be stored in a shady and airy place. This is one of the main problems, especially on village level, due the lack of space in the huts of the poor collectors.

There has been good experience with entrepreneurs sponsoring drying and storing facilities to gain better quality seeds and build a close relationship between the collectors and themselves. This includes receiving credit to process the inferior quality seeds into neem oil for the village.

Extraction technologies

Neem seeds are a valuable raw material. They contain not only insecticidal and fungicidal ingredients, but also up to 48% oil. Even the extracted neem cake can be used as fertiliser and might have effects on soil pests. There are various technologies available to extract the active ingredients of neem. Which technique should be used depends mainly on the quality required (content of Als) for the final product.

The costs of the extraction plants vary accordingly: the higher the level of azadirachtin required, the more expensive are the plants. Considering the solubility of the leading component azadirachtin, it is clear that only polar solvents should be used for extraction. Still, the cold pressed neem oil could contain up to 0.6% azadirachtin A.

Water and alcohol are the best solvents. Often methanol is the preferred alcohol because of the availability and price.

Four different types of technologies are available, the types first described being the most commonly used ones:

A) EXTRACTION with alcohol (also called one-step extraction)
B) AZADIRACHTIN-ENRICHED EXTRACTS (also called two-step extraction)
C) EXTRACTION USING CENTRIFUGES
D) EXTRACTION WITH SUPRACRITICAL CO₂

A) Extraction with alcohol (also called one-step extraction)

Advantages:

· relatively simple technology
· lower investment required
· makes use of all products, therefore no waste
· possible use of the extraction plant for other products

Disadvantages:

· quality of the final product is greatly dependent on the quality of the raw material
· often low stability/short shelf-life of the products

The neem seeds are crushed into crude powder and extracted with ethanol or methanol by maceration or percolation. The alcohol should have only a low water content, and its quality (purity) is also important.

The alcoholic extracts contain the active ingredients. Using the moving-bed contacting method, the kernels will be stirred for 3-4 hours by an overhead stirrer in a mixing-settling tank. After decantation of the crude cake, the neem solution is drained out, filtered and passed to the next procedure. The dilute neem solution will be further evaporated until a specific volume - called the "concentrated extract" (CE) has been achieved, and the solvents are recycled.

Neem kernels contain a large percentage of oil (up to 48%, average 40%), which is of considerable value on its own. The oil disturbs the extraction of the active ingredients. Therefore it would be best to remove the oil with solvents such as hexane or by cold pressing with an oil expeller. It is also possible to remove the oil content from the extract by cooling or freezing to separate the oil. The de-oiled neem cake could be further extracted with methanol to gain the azadirachtin. The oil component of neem is currently used in formulating a pet shampoo, e.g. in Thailand, or as an acaricide.

The sticky CE is dressed with carriers which will form an eventually an emulsified extract (EC) formulation

Finally the solution obtained can be bottled and supplied to the consumer.

This sort of technology is used in the smaller neem-processing plants (100 - 500 t of kernels annually) such as those in Myanmar, Thailand and Kenya. The products contain between 0.3 and 1% azadirachtin A as well as many teranortriterpenoides and other substances (residual fat, sugar etc.).

Furthermore, some of the products are formulated for a specific purpose. However, the information about formulation technology of neem pesticides is a commercial secret and often patented.

Figure 1 is a schematic diagram of a production line using a single-step extraction method for producing commercial neem-based formulations. This technology is used in Thailand, Myanmar and Kenya:

Figure 1: Example of batch extraction (from Thailand)

Machinery required for one-step neem extraction:

· Dryer for the seeds (solar dryer), thresher, oil press or hexane extraction plant, hammer mill, percolators and solvent tanks, pumps

· Evaporator, cooling tower, boiler (steamer)

· Dryer for recycling the solvents from the extracted cake, desolventiser, filling and packing equipment, cooling room, laboratory for quality control

The costs of such extraction plants (of 2000 t capacity) are approx. US$ 500 000 - 750 000 $ (CIF), without a laboratory for quality control.

The processing of neem involves many operations, as shown in Figure 2 and requires a certain mount of equipment. Figure 2 shows the equipment for commercial neem processing in Thailand.

Figure 2: Equipment required for commercial neem processing

B) Refined neem extracts - AZADIRACHTIN-ENRICHED EXTRACTS (also called two-step extraction plant)

Advantages (according to Ermel, personal communication):

· products can be easily stored (less volume) and have a longer shelf-life

· better quality in terms of azadirachtin content

· easier to fulfil the registration requirements since they contain no oil or additional substances

· easier to formulate

· homogenous quality (do not vary much from batch to batch)

· higher concentration of azadirachtin, which is required to control certain pests

· less phytotoxicity by eliminating undesirable by-products such as wax

· possible use of the extraction plant for other products

Disadvantages:

· higher investment required
· more sophisticated technology
· technology protected by patents and therefore often not available to small entrepreneurs

By applying special extraction procedures or further enrichment steps for alcoholic extracts, e.g. by fluid/fluid extraction, unwanted substances (such as residual oil, sugar, etc.) are separated and azadirachtin(s) and other tetranortriterpenoides are converted in an organic phase which is easy to vaporise. After recovery of the solvents a powder extract remains with an azadirachtin content of up to 20%. The powder can be stored and used on demand to formulate an emulsified extract (EC) with 3 - 5% azadirachtin A.

This sort of production technology is used by most plants processing commercial neem products on a large scale (1000 - 3000 t of neem kernels). In India these plants are often set up in joint ventures with partners of companies offering neem products in industrial countries such as the US.

The company Trifolio has developed a procedure starting from simple water extracts, but continuing with a fluid/fluid extraction with a special combined solvent and formulation liquid, which concentrates the Als of the non-water phase and formulates them for application in the field (Kleeberg 1996).

Other technologies

There are two further technologies which are of importance in relation to neem extraction:

C) Extraction using centrifuges

This technology is used to produce high quality oils. In a further extraction step it can be used to gain azadirachtin. In a pilot plant a powder containing 15% azadirachtin has been gained from the cake.

Investment costs: approx. US$ 3.5 - 5 million for a complete plant with an annual capacity of more than 2000 t of neem kernels.

Advantages:

· efficient exploitation of azadirachtin
· stable powder product
· neem oil, free of bitter principles
· technology can be used for other oils (e.g. castor oil, etc.)

Disadvantages:

· very high investment costs
· only profitable on a large scale
· complicated technology
· no experience concerning scaling with neem
· additional solvents are required.

D) Extraction with Supracritical CO2

This technology has recently been used in India in a joint venture with a German company and is considered a very "elegant" technology from the technical point of view.

The technology is relatively environmentally friendly, using CO₂ under high pressure and a transport carrier. The investment costs are quite high, at approx. US$ 3.5 million. Very little is known about experience with this technology so far.