Headspace-solid phase microextraction (HS-SPME) analysis of oxidized volatiles from free fatty acids (FFA) and application for measuring hydrogen donating antioxidant activity

Volatile compounds from thermally oxidized free fatty acids (FFA) at 93 °C for 200 min were analyzed by headspace-solid phase microextraction (HS-SPME)-gas chromatography (GC). Commercially available mixtures of FFA were used instead of selecting specific vegetable oils with various fatty acid compositions. As oxidation time increased, total volatiles and some individual volatiles including hexanal, 2-hexenal, 2-heptenal, 2,4-heptadienal, 2-octenal, and 2,4-decadienal increased linearly with 0.99 coefficient of determination (R²) at specific oxidation time against conjugated dienoic acid (CDA) or p-anisidine value (p-AV). Total volatiles showed the highest linearity (R²) of 0.99 and 2-heptenal showed the highest increasing slope in peak areas for 200 min oxidation. Not all oxidized volatiles increased linearly during oxidation. Availability of HS-SPME method for determining hydrogen donating antioxidant activity was tested using FFA containing serially diluted butylated hydroxytoluene (BHT) at 93 °C for 60 min. 2-Heptenal and total volatiles showed higher linearity against BHT concentration than hexanal. HS-SPME could be a useful method to determine the hydrogen donating antioxidant activity from FFA using total volatiles or 2-heptenal as oxidation markers.