Autoxidation kinetics for fatty acids and their esters

The autoxidation kinetics for n‐3 and n‐6 polyunsaturated fatty acids and their esters, which are collectively referred to as polyunsaturated fatty acids (PUFA), were investigated. Changes in the amounts of unreacted n‐6 PUFA during the entire period of autoxidation could be expressed by d Y /d t − k 1 Y (1 − Y ), were Y was the fraction of unreacted PUFA, t was the time, and k 1 was the rate constant. For n‐3 PUFA, autoxidation had to be separated into two parts. The first half of autoxidation ( Y ≥ 0.5) was expressed by the same equation as above, while the latter half ( Y <0.5) relates to d Y /d t =− k 2 Y , where k 2 was the rate constant. The apparent activation energies and the frequency factors of k 1 and k 2 were evaluated. The apparent activation energies were in a range of 50 to 60 kJ/mol for both k 1 and k 2 . The frequency factor became large as the number of double bonds of PUFA increased.