Analysis of autoxidized fats by gas chromatography‐mass spectrometry. IV. Soybean oil methyl esters

An unusual isomeric distribution of hydroperoxides has been found in soybean oil esters oxidized at low levels (peroxide values below 50). The unexpectedly high concentration of the 12‐hydroperoxide isomer is in marked contrast to the isomeric composition of oxidized pure linolenate. The different isomeric hydroperoxides observed at low levels of oxidation may contribute through their decomposition to the unique flavor deterioration of soybean oil. Quantitative gas chromatographymass spectrometry (GC‐MS) used in this study provides for the first time an answer to the basic question of which hydroperoxides contribute to the state of oxidation of soybean oil. Results of GC‐MS were confirmed by capillary gas chromatography. Analyses of highly oxidized soybean esters (peroxide values 468 and 2352) reveal the same main compounds as those found in oxidized pure linoleate, together with small amounts of oleate and linolenate hydroperoxides.