Kinetics of geometrical isomerization of unsaturated FA in soybean oil

Abstract

AbstractLaboratory treatment of soybean oil were carried out at the following conditions: atmospheric pressure in the presence of air or nitrogen at different temperatures ranging from 160 to 250°C for 12 to 72 h. These conditions were used to study geometric isomerization of cis,cis‐linoleic and cis,cis,cis‐linolenic acid in the presence or in the absence of oxidative degradation reactions. Based on these experiments, a model of consecutive, parallel reactions was developed to describe the reaction steps occurring in the soybean oil during heating at constant temperature. For both cis,cis‐linoleic and cis,cis,cis‐linolenic acid, the reaction of formation isomers followed a first‐order reaction, and the rate constant of isomerization varied according to the Arrhenius law. The isomerization rate constant for linoleic acid was 9.57×10−3±0.50 h−1 in the presence of oxygen and 7.39×10−3±0.39 h−1 in its absence, and the isomerization rate constant for linolenic acid was 1.18×10−1±0.10 h−1 in the presence of oxygen and 0.87×10−1±0.07 h−1 in its absence (all obtained at 250°C).