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

Abstract

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 firstorder 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.Paper no. J8867 in JAOCS 76, 73-81 (January 1999).

Comparison of geometrical isomerization of unsaturated fatty acids in selected commercially refined oils

“…A deodorization temperature of 220-230 o C seems to be the critical point above which C18:3 acid isomerization substantially increases. The critical temperature is higher for C18:2 acid, over 240 o C (Henon et al, 1999). Kellens (1997) reported that chemical refining should be done at [230][231][232][233][234][235] o C and physical refining at 235-240 o C to obtain deodorized oils with low levels of trans FA (Ͻ 1%).…”

“…Refining has the purpose of not only eliminating impurities, but also minimizing trans FA formation (Kellens, 1997). Because the quality variables for refined vegetable oils include the lowest possible content in trans fatty acids, this is more and more important as a contemporary quality criterion (Leon-Camacho et al, 1999;Henon et al, 1999).…”

The retina is more susceptible than the brain and the liver to the incorporation oftransisomers of DHA in rats consumingtransisomers of alpha-linolenic acid

“…The detailed composition of the diets is presented in Tables I and II. The diets were prepared from oil mixtures kindly provided by Lesieur (Coudekerque-Branche, France). Briefly, bleached canola oil was used after deodorization for 52.5 h at 205 • C under 3 mbar [28] to provide trans α-linolenic acid. Isomerized sunflower oil (270 • C, 18 h) was added in the mixtures in order to balance the trans linoleic acid (18:2 n-6) levels.…”

Role of the central R&D laboratories of an international group in the field of Food-Feed Safety

“…Each process is evaluated for its effectiveness at removing contaminants (pesticide residues, heavy metals) and unwanted compounds (prooxidative metals, degradation products) and the risk of formation unwanted compound (trans fatty acids dimer, trimer, polymer). (For more details of our results see [1][2][3][4]6]. )…”