|Small Scale Processing of Oilfruits and Oilseeds (GTZ, 1989, 100 p.)|
|1. Oil Plants and their Potential Use|
Vegetable oils and fats can be consumed directly or be the rawmaterial for further processing. Below, some of the more important products derived from vegetable oils are discussed. Most of these products are manufactured by a specialized industry.
Refined salad and cooking oils
In food, vegetable oils are normally preferred with a bright colour and a bland taste. Neutrally tasting salad and cooking oils are generally made from peanut, sunflower, sesame, maize or cotton seed oil by a complex refining operation which includes neutralization, bleaching and deodorization. Soyabean oil and rape seed oil are less suitable as they possess a characteristic flavour after deodorization.
Margarines are an emulsion of fats in water, in which the water compound is dispersed as in butter made from milk. The fat needs to have a certain plasticity and to melt readily in the mouth. Such a fat is obtained by mixing, for instance, coconut and/or palmkernel oil with other oils which are hydrogenated to an appropriate degree.
As the product contains water it is easily spoiled by bacterial contamination or oxidation. Margarines need therefore to be tinned or stored under refrigeration.
Pure oils and fats can be kept much better. In India and other tropical countries butter is therefore processed into a pure oil, known as ghee.
Fat is a highly necessary ingredient in baked goods as it not only contributes to the flavour but also to the physical structure of the product. To provide the fats with the required so-called shortening" value, a large range of special products are on the market for the bakery industry which are made by the hydrogenation of vegetable oils and compounding of fats from different origins.
Soaps are commonly made by boiling a fat with strong Iye. The effectiveness of such a soap depends mainly on its surface activity properties and its solubility. Both depend largely upon the length of the chain and the unsaturation of the fatty acids which form the soap.
Soaps made from the higher fatty acids (e.g. stearic) are very efficient detergents, but have only limited solubility, which limits their usefulness as a household soap. Soaps of the lower fatty acids (e.g. Iauric acid) are freely soluble but are less efficient as a detergent.
An optimum balance can be reached on the basis of a fat from animal origin or palm oil, mixed with 15 % to 30 % of coconut or palmkernel oil.
Mineral oils have superseded fatty" oils (i.e. animal and vegetable oils) as lubricants as they are more stable and cheaper. However, fatty oils have certain special advantages to mineral oils, since they have a superior ability to cling to metal surfaces in a thin film. Suitable fatty oils are those which are sufficiently saturated to be stable. They are used for lubricating light machinery. Castor oil is more viscous than ordinary oils and hence is suitable for lubricating heavy machinery. The latter is also used as a base for fluids in hydraulic systems.
Cheap illuminants from petroleum have virtually eliminated vegetable oils as burning oils, except in isolated regions. However, candles based on paraffin wax or beeswax need a hardening agent to assist in maintaining their shape in hot weather or to burn without dripping. Next to stearic acid, very highly hydrogenated oils can be used for this purpose.
Stable fats and oils can be used in cosmetics such as, for instance, palm oil or shea nut butter in creams and castor oil in alcohol-based hair dressings. In pharmaceuticals they can be used to carry fatsoluble substances as vitamin concentrates. They can also be used to prevent infestation of crops by insects.
Highly unsaturated oils are used as drying oils in paints and varnishes. Linseed oil is important in this regard, followed by soyabean oil. Castor oil can be chemically dehydrated to give a fast drying oil, suitable for use in water-resistant varnishes and enamels.