Coconut oil as a calibration matrix for headspace gas chromatographic determination of hexanal in edible oils

Abstract

Oxidation of unsaturated fatty acids of edible oils results in off-flavours, in a decrease in the nutritional properties and in the formation of toxic compounds. Hexanal is a suitable marker of the oxidation process. A new solvent, coconut oil, was suggested for hexanal quantification by static headspace extraction-gas chromatography. Sample equilibration temperature, time, weight and injection time were determined to provide the highest extraction to the headspace efficiency. At the optimized extraction conditions, the hexanal detection limit was 30 µg kg^–1, linearity was 0.9977 for a concentration range of 50 µg kg^–1 – 2 g kg^–1 and repeatability of the results was 1.1%. The effect of heating on hexanal formation in four edible oils (olive oil, sunflower oil, rapeseed oil and linseed oil) was investigated. The biggest quantity of hexanal was observed in sunflower oil and it significantly increased after heating. Rapeseed oil was the most resistant to the oxidation at elevated temperatures. For linseed oil hexanal is not the most relevant oxidation marker as hexanal is not the main volatile oxidation product.