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Measurement of peroxide values in oils by triphenylphosphine/triphenylphosphine oxide (TPP/TPPO) assay coupled with FTIR-ATR spectroscopy: Comparison with iodometric titration

Deyrieux C., Villeneuve P., Baréa B., Decker E.A., Guiller I., Salaun F.M., Durand E.. 2018. European Journal of Lipid Science and Technology, 120 (8) : 10 p..

DOI: 10.1002/ejlt.201800109

Hydroperoxides (LOOH) measurement is a common technique to determine the degree of oxidation of oils and fats. Although it appears to have some limitations (time consuming, and uses of toxic solvents as chloroform), the iodometric titration is one of the most common methods. Herein, an alternative method by measuring the oxidation level using Fourier transform infrared (FTIR) with an attenuated total reflectance mode (ATR), based on the stoichiometric conversion of triphenylphosphine (TPP) into triphenylphosphine oxide (TPPO) by hydroperoxides, is proposed. The FTIR-ATR spectroscopy allows for a simple and accurate detection of the TPPO formed by selective reaction with LOOH, with measurement of its specific adsorption band at 542cm_1. Calibration is made with TPPO solubilized in butan-2-one and covers a range of peroxide values (PV) from _2 to _800mEqkg_1. The comparison of the iodometric titration and TPP/TPPO assay is performed with standard hydroperoxides (tert-butyl hydroperoxide and cumene hydroperoxide). The iodometric titration shows higher PV overestimations in comparison with the TPP/TPPO assay, for both hydroperoxides. An accelerated oxidation of different oils is assessed with the two methods, and the results confirm this observation since higher PV values are measured with the titration method. The TPP/TPPO assay coupled with the ATR-FTIR spectroscopy appears as a simpler and faster assay, which may limit overestimation and use of toxic solvents, especially suitable for routine analysis of oil and fats. Practical Applications: One of the first indicator of oxidation in oils and fats is the presence of hydroperoxides, therefore, it is important to find a reliable method to assess these oxidation products. One of the most common methods to determine lipid hydroperoxide (LOOH) concentrations is iodometric titration. Although this method is simple to set up, it is labor-intensive, time consuming, and uses a lot of solvent. TPP/TPPO assay coupled with FTIR-ATR spectroscopy is a good alternative to the iodometric method since it allows a fast and robust hydroperoxide measurement, with minimal use of organic solvents. This rapid peroxide value determination can be adapted for routine quality control analyses, especially for oxidation in real-time and accelerated aging assays to evaluate oxidative stability during shelf-life, for industrial purpose or lab scale experiments.

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