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.
