Analysis of thermoxidation kinetics of milk fat

The thermoxidation of four different milk fat samples was studied using isoconversional method. The milk samples contained different ratio of unsaturated to saturated fatty acids of 0.7, 0.86, and 1.36 (MF1, MF2, and MF3, respectively), and a hydrolyzed milk fat sample (90% free fatty acids) with a ratio of 1.40 (MF4). The thermoxidation has been conducted under non-isothermal oxidation from 380 to 520K using five different heating rates (3, 6, 9, 12and 15 K min-1). The Kissinger-Akahira-Sunose (KAS) method was used to calculate the activation energy as a function of the extend of themroxidation. The obtained dependencies were interpreted in terms of oxidation mechanisms. The activation energy values were 100.10, 84.53, 80.41, and 121.44 kJ mol-1 for MF1, MF2, MF3, and MF4, respectively. The thermoxidaiton of milk fat in the form of triacylglycerol was best described by Avrami-Erofeev model (A3), while the thermoxidation of free fatty acids was described by a frist-order model (F1). The calculated kinetic triplet were used to simulate the thermoxidation of milk fat and showed good agreement with the experimental data