Volatile compounds as indicators of conjugated and unconjugated linoleic acid thermal oxidation

In this research, volatiles arising from heating of conjugated (CLA) and unconjugated (LA) linoleic acid, in different chemical forms (free acids, methyl esters, and homogeneous TAGs) have been studied. A solid phase micro‐extraction (SPME) coupled with GC–MS was used to analyze the volatile compounds produced during heating at 180°C for different times (15, 30, 45, and 60min). Numerous types of volatiles have been identified such as aldehydes, furan fatty acids (FA), alcohols, methyl esters, and methyl‐oxoacids. Results showed that aldehydes were the main volatile compounds both in CLA and LA, even if some differences were found between conjugated and unconjugated systems. In particular, heptanal and trans‐2‐ octenal were detected mainly in CLA forms, while trans‐2‐heptenal in LA. Among furan FA, 2‐pentyl‐furan content was higher in LA than in CLA at all treatment times, while 2‐hexyl‐furan was detected in free fatty acid and methyl ester forms of CLA and it was never detected in LA model systems. Among alcohols, 1‐octen‐3‐ol was found only in LA forms. Methylated forms of CLA and LA provided high contents ofmethyl esters, among whichmethyl octanoate was the most represented. Therefore heptanal, trans‐2‐octenal, 2‐hexylfuran could be considered as characteristic compounds produced during CLA‐rich sample oxidation.