Analysis of Volatile Compounds Formed from Fish Oil Heated with Cysteine and Trimethylamine Oxide

Volatile compounds formed in the headspace of menhaden fish oil heated with cysteine or cysteine and trimethylamine oxide (TMAO) were analyzed by gas chromatography and gas chromatography/mass spectrometry. Among >150 gas chromatographic peaks, 105 compounds were positively identified. Among the 45 compounds identified in the headspace of heated fish oil without TMAO or cysteine, the major compounds identified were aldehydes. When fish oil was heated with cysteine, the number of volatiles formed increased (77 compounds identified), and the addition of TMAO further increased the number of volatiles formed (87 compounds identified). The major compounds identified were 26 heterocyclic compounds: 8 furans, 8 pyridines, 1 pyrrole, 4 thiazoles, 3 thiazolines, and 2 thiophenes. TMAO acted as a promoter of the oxidative degradation of fish oil and cysteine rather than as a reactant for the nitrogen sources. The heterocyclic compounds identified are believed to contribute to the flavor of cooked fish.