Oxidation kinetics of bioactive milk lipids using differential scanning calorimetry

The consumption of certain fatty acids naturally found in milk has been associated with several health benefits. These fatty acids are known as bioactive lipids (BML), and they provide beneficial effects beyond their basic nutrition. Examples of such fatty acids are conjugated linoleic acid (CLA, C18:2), trans-vaccenic acid (TVA, C18:1 t11), eicosapentaenoic acid (EPA, C20:5 ω3), and docosahexaenoic acid (DHA, C22:6 ω3). Dairy processors are actively exploring ways to incorporate BML in their formulations via fortification and enrichment protocols. Chemically, BML are unsaturated fatty acids containing at least one double bond in their structure, which makes them more prone to oxidation than the saturated fatty acids. In this work, the oxidation kinetics of DHA, EPA, CLA, and TVA was studied using differential scanning calorimetry (DSC) under different heating rates (3, 6, 9, 12, 15 and 18°C min−1) in the temperature range of 50–300°C. The Kissinger-Akahira-Sunose (KAS) method was used to evaluate the kinetic triplet [activation energy, Ea; pre-exponential factor, A; and reaction model, f(α)]. The Ea values were 59.30 ± 4.75, 47.17 ± 3.15, 55.46 ± 2.75, and 57.43 ± 3.01 kJ mol−1 for DHA, EPA, CLA, and TVA. The isoconversional analysis revealed that the Ea values does not vary with the degree of oxidation, indicating that the oxidation of BML can be explained by a single-step approach. Several reaction models were tested, and it was found that BML follow a first-order reaction. The calculated kinetic triplets are used to predict the oxidation, and the simulated data agreed well (R2 = 0.998) with the experimental data. The use of isoconversional methods opens up opportunities in exploring the oxidation of milk fat and it offers advantages over the traditional kinetic methods