Heteronuclear NMR Method as a Replacement for Classical POV Titration in the Determination of Hydroperoxides in Lipids and Lecithin

Hydroperoxides are the primary oxidation products in the degradation of fats. Classical titration methods for determining the Peroxide Value (POV) are unreliable due to their non-specificity and incompatibility with lecithins. We present a novel NMR-based method that employs a redox reaction on a modified phosphoester and detects the reaction specifically using ¹⁹F NMR spectroscopy. This approach eliminates signal interference from complex lipid mixtures.

The method demonstrates high specificity for hydroperoxides, converting them into alcohols while the reagent is oxidized. All reactants and products can be quantified precisely. The sensitivity of this method is highlighted by the measurable changes in chemical shifts in the ¹⁹F NMR spectrum, enabling POV determination even in trace amounts.

A detailed kinetic study of the second-order redox reaction was conducted, and the method was validated using calibrated partially oxidized triolein as a standard. As a primary method, NMR outperforms traditional titrations. Furthermore, this technique allows for the determination of POV in complex lipid systems, such as krill oil and lecithins, regardless of whether they are native or modified.

In addition, the ³¹P NMR spectrum enables simultaneous quantitative analysis of phospholipids, providing a "one-pot" reaction and analysis approach. Secondary oxidation products such as aldehydes can also be directly identified in the ¹H NMR spectrum, along with iodine and acid values, which would otherwise require separate titrations.

This novel method provides a comprehensive, reliable, and efficient alternative to classical POV titration, broadening the scope of lipid oxidation analysis in complex systems.