Principles of preservation and processing methods

The general principles of preservation include:

· destruction of enzymes (a complex organic substance which in solution produces fermentation and chemical changes in other substances apparently without undergoing any change itself) in the raw material and contaminating micro-organisms by heat (sterilization) during processing;

· elimination of as much water as possible from the oil to prevent microbial growth (bacterial activity, or disease-causing germs) during storage. The oil therefore has a long shelf life due to its low moisture content.

· Proper packaging and storage of the extracted oil to slow down chemical deterioration (rancidity).

The method used to extract vegetable oil depends on the type of raw material available. Raw materials may be grouped according to the part of the plant that contains the fat or oil (seed, bean, nut or fruit). The main difference in raw materials is the moisture content. Raw materials with low moisture content include seeds and beans and some nuts, which are dried on harvest. Palm fruit, olive fruits and some coconuts are processed wet.

Only seeds, nuts and fruits that contain considerable amounts of edible oil are used for small-scale oil extraction. Other types (for example maize) may contain edible oil, but the quantities are too small for economic processing on a small-scale. However, not all oil-rich seeds and fruits have edible oil; some contain toxins (poisons, usually of bacterial origin) or have unpleasant flavours; these are used only for varnishes, paints, etc. Others, (for example castor oil) need very careful processing to make them safe for use as medicines. These are not suitable for small-scale processing.

Palm fruit contains about 56 percent oil (25 percent on a fresh fruit bunch basis) which is edible with no known toxins. It is thus suitable for small-scale processing.