Physical refining of edible oils

Crude oils obtained by oilseed processing have to be refined before the con sumption in order to remove undesirable accompanying substances, The tradit ional alkali refining is often replaced by physical refining in which the u se of chemicals is reduced. The most widely used method is steam refining. The crude oil quality is very important in order to obtain high quality ref ined oil. Furthermore, the oil should be efficiently degummed to remove pho spholipids as well as heavy metals and bleached to remove pigments. The mos t important step consists of the application of superheated steam under low pressure and at temperatures higher than 220 degrees C. Both free fatty ac ids and objectionable volatiles, formed by cleavage of lipid oxidation prod ucts, are removed. A disadvantage is the partial loss of tocopherols. Side reactions, particularly isomerization of polyunsaturated fatty acids, shoul d be minimized. The quality of physically refined oil is close to that of a lkali refined oils, but losses of neutral oil are lower and the environment is less polluted. Among other methods of physical refining the application of selective membranes is promising.