Deodorization of vegetable oils. Part I: Modelling the geometrical isomerization of polyunsaturated fatty acids

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Laboratory-scale treatments of canola oils similar to deodorization were carried out by applying the following conditions: reduced pressure with nitrogen or steam stripping at different temperatures ranging from 210 to 270°C for 2–65 h. The formation of the group of trans linolenic acid isomers follows a first-order reaction and the kinetic constant varies according to the Arrhenius’ law. Similar results were observed for the trans isomerization of linoleic acid. Based on these experiments, a mathematical model was developed to describe the isomerization reaction steps occurring in linoleic and linolenic acids during deodorization. The calculated degrees of isomerization are independent of the composition of the oil but related to both time and temperature of deodorization. The degree of isomerization of linolenic acid is unaffected by the decrease of this acid content observed during the deodorization. Deodorization at about 220–230°C appears to be a critical limit beyond which the linolenic isomerization increases very strongly. The newly established model can be a tool for manufacturers to reduce the total trans isomer content of refined oils, and was applied to produce a special selectively isomerized oil for a European Nutritional Project.