Basically
vegetable oil has following impurities which needs to
be removed.
1) PHYSICAL IMPURITIES:
Left over particles of oil seeds
etc. By simple filteration process these impurities
are removed.
2) PHOSPHATIDES,
GUMS AND WAXES:
During pretreatment process gums
and other impurities are either separated out, either
through batch degumming or through continuous process
with help of centrifugal separators. When impurities
are only in small quantities Gum conditioning process
is adopted, where in gums are just precipitated and
are removed in next neutralising process.
3) FREE FATTY
ACIDS:
Popularly known as F.F.A. all
vegetable oils are compound formed by Glycerin and Fatty
Acids when Fatty Acid separates out from the bond with
Glycerin they are termed as Free Fatty Acids. The free
Fatty Acids are generally removed by neutralising them
with alkalies like caustic soda. The soap stock formed
and the oil are then separated out by decantation process
in Batch Neutralising or by centrifuge separation in
continuous Neutralising.
4) COLOURING
PIGMENTS:
Depending on the quantity and
type of colour pigments present in the oil, oils have
colour ranging from light yellow, reddish} to dark brownish
(as in crude cotton seed oil). To give uniform, colour
it is essential to bleach the oil with the help of bleaching
agents like bleaching earth / activated carbon. Bleaching
agents absorbs the colouring pigments. By filteration
process the spent bleaching agent is filtered out. Sometimes
caustic treatment in neutralising section also reduces
the colour of oil specifically in cotton seed oil. In
case of palm oil colour is also reduced by heat treatment.
Bleaching operation is performed either as batch process
in smaller capacities or as continuous operation in
large capacity plants.
5) ODOUR:
Every oil has its own district
odour sometimes pleasing odour sometimes unpleasant
odour. Neutralising and bleaching process also adds
odour to the oil which is unpleasant. It is therefore
essential to remove the odour from oil. Deodorisation
is the process to remove odiferous matter from vegetable
oils. The odour is removed by injecting open steam in
the oil which is heated to high temperature and kept
under high temperature and kept under high vacuum. The
odiferous matter distills off at high temperature and
high vacuum and is carried away through vacuum system.
The oils is cooled.
6) WAXES:
Some oil like sunflower seed
oil and maize germ (corn) oil have waxes present in
them. At low temperature waxes appears and gives hazy
appearance to oil. Consumer does not prefer such hazy
appearance. |