Distillative deacidification

Part of the unsaponifiable matter (such as tocopherols, sterols, and sterolesters) is distilled together with the free fatty acids during deodorization/deacidification, as... 

Electrodialysis is a well-proven technology with a multitude of systems operating worldwide. In Europe and Japan, electrodialysis dominates as a desalting process with total plant capacity exceeding that of reverse osmosis and distillation [3]. Electrodialysis with monopolar membranes is applied to different food systems, to demineralization of whey [5-8], organic acids [9], and sugar [10,11], separation of amino acids [12] and blood treatments [13], wine stabilization [14—16], fruit juice deacidification [17-19], and separation of proteins [20-22]. These applications use the sole property of dilution-concentration of monopolar lEMs in a stack of as many as 300 in an electrodialysis cell. 

Fats (oils) with a high content of free fatty acids require relatively high amounts of alkali for extraction, resulting in an unavoidably high loss of neutral fats (oils) due to alkaline hydrolysis. Therefore, extraction with alkali is frequently replaced by deacidification by distillation in these cases (14.4.1.5). 

In the next step, fatty acids are separated from the oil by neutralisation (deacidification or afkahne refining) with sodium hydroxide solution (which is also effective in the removal of toxic gossypol from cottonseed oil see Section 9.11). The free fatty acid content varies widely within 0.5-1.5% in seed oils from raw materials grown in a temperate zone. After neutrahsation, the fatty acid content falls below 0.1%. The resulting soaps are separated as soap stock and typically used in animal feed. Tropical oils, such as palm and coconut oils, contain 3-7% free fatty acids. It is therefore preferable to separate the free fatty acids together with volatiles by distillation in the end stage of physical refining process. In this case, the main components of the distillate are free fatty acids. 

Bleaching is achieved by adsorption on activated bleaching clays (sorbents of the aluminium silicate type) or in combination with other adsorbents (such as activated carbon, also known as activated charcoal) to remove oil soluble pigments (such as carotenoids and chlorophylls), residual phosphoHpids, and eventually soap residues resulting from the deacidification process. Volatile substances are removed by deodorisation via steam distillation under reduced pressure. The volatile compounds are mainly responsible for the unpleasant smeU and aftertaste of cmde oil, so this process provides organoleptically neutral, indifferent oils. 

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