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close this bookSmall Scale Processing of Oilfruits and Oilseeds (GTZ, 1989, 100 p.)
close this folder1. Oil Plants and their Potential Use
View the document1.1 Characteristics of vegetable fats and oils
Open this folder and view contents1.2 The major oil plants
View the document1.3 By-products
View the document1.4 Further processing
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1.1 Characteristics of vegetable fats and oils

In principle, there are no essential differences between vegetable fats and oils. The distinction is only a question of melting points, fats being solid and oils being liquid at the temperature concerned.

Chemically, fats and oils are glycerides. A glyceride is a combination of glycerol with fatty acids, a so-called ester. This compound can be split up by naturally occurring enzymes, which are generally present in the rawmaterial, and by alkali. The latter reaction is, essential for the production of soap. In the case of enzymes, free glycerol and free fatty acids are formed, a process that also takes place when fats are digested in the human body.

The fatty acids found in vegetable fats and oils are generally based on 12 to 20 carbon atoms. They can be saturated or unsaturated. Saturated fatty acids contain only carbon atoms linked to not less than two hydrogen atoms; unsaturated fatty acids contain atoms with fewer hydrogen atoms, resulting in so-called double bonds,

The more common saturated fatty acids are referred to by name, e.g.:

- lauric

(C12)

- myristic

(C14)

- palmitic

(C16)

- stearic

(C18)

- arachidic

(C20)

The same applies for unsaturated acids, e.g.:

- oleic (C18) with one double bond (9:10),
- linoleic (C18) with two double bonds (9:10, 12:13),
- linolenic (C 18) with three double bonds (9:10, 12:13, 15:16).

Vegetable fats and oils have high calorific values and are therefore important sources of energy for the human diet. Besides, they contain so-called “essential" fatty acids (i.e. those necessary for good health) which animals cannot synthesize. Vegetable fats and oils also serve as carriers of the fat soluble vitamins, such as A, its provitamine Carotene, D, E (tocopherol) and K. Furthermore, fats and oils are, of course, important in giving taste to the food.

Fats and oils are relatively stable products. However, the quality of the fats or oils can be harmed by reactions which cause the formation of free fatty acids or rancidity. These reactions are caused by enzymes, air or moulds (so- called ketone rancidity). Fats can be split by active enzymes if the required reaction conditions are fulfilled (high temperature and high moisture content).

To prevent enzymatic reactions, oxidation and/or mould growth, vegetable oils and fats should be stored:

- at a relatively low temperature, - airtight,
- dry,
- clean and
- in the dark.

Proper storage can be in dry, clean containers such as bottles, tins or drums, filled to the top and well closed. To prevent oxidation, the oil should contain an antioxidant such as tocopherol (vitamin E). As mentioned above, tocopherol is to some degree - depending on the nature of the raw material - already present in unrefined oils and, thus, acts as a natural antioxidant.

When stored in this way, vegetable oils and fats have a “shelf life" (remain fresh) for at least six months.