[Contamination and secondary reactions in the processing of dietary fats]

The contamination of dietary fats and oils can have various origins: contamination of the raw materials that could not be eliminated by the industrial process; refining completely eliminates this type of contamination; contamination with one of the processing aids can occur if the process is not properly conducted; contamination with packaging materials will increase with the storage duration of the finished product (in the case of vinyl chloride monomer and styrene contamination); only the strict control and adequate choice of the materials and packaging conditions will allow complete elimination of this contamination type. The presence of small amounts of another fat (in vegetable margarines for instance) should also be mentioned although it is not a real contamination. The secondary reactions that may occur during the processing of dietary fats are primarily due to unwanted chemical reactions leading to the formation of fatty acid or native glyceride isomers (e.g. formation of geometric isomers during deodorization, formation of position isomers during hydrogenation). In the present stage of knowledge, it is fairly easy to avoid secondary reactions during deodorization, those that take place during hydrogenation are not yet under control, however.