Operations Performed
Vegetable oil is a vital ingredient used by human in their regular diet. Vegetable Oil adds value taste to the food. Depending on Geographical locations different varieties of oils are popular in different region. Nature has given different individual characteristics to all vegetable oils.
Vegetable oil refinery in our country is relatively a recent technology inducted in the past two decades. Just for knowledge: In vegetable oil refining, there are two types of process available viz. chemical refining & physical refining. In chemical refining, there are three main process involved viz. Degumming & Neutralizing, Bleaching & deodorizing for removal of various impurities from the raw oil. So far large quantities of expeller/solvent groundnut oil, rapseed oil are used for edible purpose directly with simple filtration. They are physically purified and they are known as double filtered oils. However, due to more and more awareness about various health aspects, like harmful effects of various natural impurities of raw oils, such as free fatty acid (FFA), the cause for the cholesterol increase, plant pigments, phosphatides etc. consumers prefer refined vegetable oils against simple filtered oils. Oil refining industry has developed considerably in the last one decade. Furthermore, due to the chronic shortage of vegetable oils in our country, many oils, which are not previously used for human consumption, are being processed and used for human consumption.
Basically vegetable oil has following impurities which need to be removed:
- Physical Impurities.
- Phosphatides, Gums and Waxes.
- Free Fatty Acids (FFA).
- Colouring Pigments.
- Odor.
- Waxes.
Let us have a brief introduction about each in detail:
PHYSICAL IMPURITIES:
Left over particles of oil seeds etc. By simple filtration process these impurities are removed.
PHOSPHATIDES, GUMS AND WAXES:
During pretreatment process gums and other impurities are separated out 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.
FREE FATTY ACIDS:
Also 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 neutralizing them with alkalis like caustic soda. The soap stock formed and the oil are then separated out by decantation process in Batch Neutralizing or by centrifuge separation in continuous Neutralizing.
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 filtration process the spent bleaching agent is filtered out. Sometimes caustic treatment in neutralizing 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.
ODOR:
Every oil has its own distinct odor sometimes pleasing odor sometimes unpleasant odor. Neutralizing and bleaching process also adds odor to the oil which is unpleasant. It is therefore essential to remove the odor from oil. Deodorization is the process to remove odiferous matter from vegetable oils. The odor 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 are cooled.
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.
Dewaxing process is adopted for separation of waxes from oil. Oil is cooled and chilled in crystallisers the waxes are crystallized. The wax crystals are separated out either by cold neutralization in centrifuges or more common method of separation is filter them out in horizontal pressure leaf filters.
The oil which is thus treated for removal of gums, free fatty acids, colouring matter and odor is refined oil. In oils like palm oil, free fatty acids are removed during deodorization itself without chemical caustic treatment and hence process is called physical refining.