Storage Duration and Added Docosahexaenoic Acid Modify the Rates of Esterified and Free Oxylipin Formation in Infant Milk Formula

Infant milk formulas often contain docosahexaenoic acid (DHA), a highly unsaturated fatty acid that is prone to oxidation. Previously, we reported in oil that the esterified lipid pool is more prone to lipid oxidation than the free pool. However, it is unknown whether added DHA modifies lipid oxidation in infant formula. In the present study, we quantified lipid oxidation rates in infant milk formula containing canola oil (F1) or canola oil supplemented with DHA-ethyl ester (F2). Lipid oxidation kinetics were determined by quantifying esterified and free oxylipins using liquid chromatography-tandem mass spectrometry (LC-MS/MS) during storage for 21 days at 4 degrees C. Esterified oxylipins increased in concentration within 3 and 7 days of storage in F2 (with DHA) and F1, respectively. Free oxylipins appeared 7 and 14 days later in F2 and F1, respectively. The kinetic estimates revealed that esterified oxylipins formed at a faster rate in both formulas compared to free oxylipins. Surprisingly, in F2 (which contains DHA), the rates of formation of both esterified and free linoleic acid and alpha-linolenic acid-derived oxylipins were higher than in F1. This study demonstrated that in food systems, DHA promotes the oxidation of other PUFAs, and that triacylglycerol/esterified lipids are preferentially oxidized over free fatty acids, highlighting the role of triacylglycerols in lipid oxidation.

Automated summary

DHA in infant milk formulas promotes oxidation of other polyunsaturated fatty acids and esterified lipids are preferentially oxidized over free fatty acids.