The purpose of bleaching (or decolorizing) is to reduce the levels of pigments such as carotenoids and chlorophyll, but it also further removes residues of phosphatides, soaps, traces of metals, oxidation products, and proteins. These trace components interfere further processing. They reduce the quality of the final product and are removed by adsorption withactivated clay and silica.
In integrated crushing / refining plants the used bleaching earth is brought back into the meal. Bleaching earth originating from pure refining plants and / or hardening plants, which can contain nickel is excluded from recycling into the feed materials and is disposed of outside the feed sector.
If vegetable oils contain unacceptable levels of PAH's (polycyclic aromatic hydrocarbons), activated carbon is added to absorb and eliminate the PAH's. The used activated carbon is separated by filtration and disposed of in a suitable way outside of the food and feed sector.
If also heavy polycyclic aromatic hydrocarbons are present, activated carbon shall be used for their removal. Dosage of these adsorption agents should be adapted to ensure the removal of the specific substances. The bleaching clay containing all these substances is separated by filtration. Those processes are partly done under vacuum and at temperatures below 150°C.
The purpose of deodorization is to reduce the level of free fatty acids and to remove odours, off-flavours and other volatile components such as pesticides and light polycyclic aromatic hydrocarbons by a stripping media. Careful execution of this process will also improve the stability and the colour of the oil, whilst preserving the nutritional value.
The deodorization process is carried out under vacuum (0.5 – 8 mbar) and at temperatures between 180° - 270°C, and using a stripping media.
Conditions should be adapted within these ranges as appropriate to ensure the removal of the specific substances.
Careful execution of these four processing steps ensures that fully refined oils possess good organoleptic and physicochemical qualities. The extent of protein removal is of critical importance to absence of allergenicities.