Edible oil refining

Raw vegetable oil, obtained from seeds by pressing, solvent extraction, contains free fatty acids and other components such as phospholipids, waxes, peroxides, aldehydes, and ketones, which contribute to undesirable flavor, odor, and appearance;[1] for these reasons, all the oil has to be refined.

Similarly to the previous treatment, the solution coordinates metals and phospholipids, however the chelating agent used, such as EDTA, is able to remove more than 90% of phosphorus content in the matrix such as rapeseed oil.

Using this principle, it is possible to separate not only gums, but also other impurities, such as fatty acids, to limit further processes of the oil and reduce waste and energy to purify it.

However, it is required the use of hexane to form the micelles, and in the processes in which is possible to avoid it, the flux is low, so it is not feasible on an industrial scale.

[2][1] Neutralization consists of the removal of free fatty acids, which come from the partial natural hydrolysis of triglycerides.

Another technology has evaluated the esterification of free fatty acids with glycerol in order to reclaim vegetable oil, both with metal catalysis and by using microorganisms.

[5] Since crystallization is a difficult process, and natural oils show different composition and botanical sources, different variants were developed, in which different temperatures, residence times are used and the presence or introductions of surfactants, phospholipids or organic solvents are employed to optimize the separation.

[5][3] Raw oil contains various pigments such as chlorophylls, carotenoids, xanthophyll, etc., which can cause problems with subsequent treatments or can color the final product during storage.

This process aims to remove them using bleaching earth, which is a class of acidic clay that is capable to absorb oil's pigments and also metals.

Oil is mixed with this earth in 0.2-2% weight ratio, then vacuum is applied and the suspension is heated at 70-140 °C to both improve the decomposition of fatty acid peroxides and the absorption of the pigment.

[4] During the final steps of the refining process, the oil is stripped with vapor at a high temperature to remove all remaining undesirable odors and flavors present in it.

[8] Soapstock comes from the neutralization step and it contains alkaline water, sodium salts of fatty acid, residual tri -, di- and Monoglycerides, and other minor components.

However, it has been recently shown that waxes can be submitted to solid state fermentation, using Starmerella bombicola in combination with sources of sugar, such as beetroot molasses, and it can be exploited to produce surfactants.