Nonadiene isomers as potential green flavor components of autoxidizing fish oil

Fish oil oxidation leads to the formation of volatile compounds that contribute to undesirable off-flavors, primarily through free radical mechanisms that produce hydroperoxides and their decomposition products, including aldehydes, ketones, and furan derivatives. This study focuses on the identification of volatile compounds formed during the autoxidation of menhaden oil under three different conditions: (1) exposure to light for 11 days, (2) heating at 121 °C for 80 min, and (3) storage in the dark at 40 °C for 48 h. Gas chromatography-mass spectrometry (GC–MS) analysis confirmed the production of three isomers of nonadiene, including the potent aroma compound 2,4-nonadiene, which has a low aroma threshold (7.8 ppb in water) and contributes to green, fishy off-notes. Notably, 2,4-nonadiene is predominantly derived from omega-6 fatty acids rather than omega-3, a novel finding. Additionally, olfactory detection identified green compounds between C4 and C5 ethyl esters from oxidized menhaden oil, though GC–MS spectra suggested co-elution of compounds, complicating identification. This research highlights the unique formation pathways of nonadiene isomers and offers new insights into controlling oxidative off-flavors in fish oil products, with implications for improving product quality and shelf life.