Lipid autoxidation of fish, lard, corn and linseed oils by isothermal calorimetry
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Isothermal calorimetry is recognized as a suitable method for the determination of both thermodynamic and kinetic parameters associated with a chemical reaction. However, the oxidative stability of oils and fats is often expressed with just a simple index, the so-called oxidative induction period (IP). The aim of this work is to extend the information that can be derived from the calorimetric trace by including also the extent of the monomolecular and bimolecular periods. For this purpose, fish and lard oil samples have been analyzed by isothermal calorimetry at different mild temperatures (from 40 to 80°C). The calorimetric traces were converted in the reaction order vs time. From this curve, it was possible to identify the extent of the monomolecular, bimolecular and termination period of the autoxidation process. The results for fish oil at 80°C were 40, 224, and 470 min, respectively. These data were compared with those obtained with other oil samples, such as linseed (390, 1102 and 1680 min), lard (30, 104 and 1134 min) and corn (2060, 1121 and 1160 min). The results were discussed in comparison with the results of fatty acids profile and the antioxidant activity.