Action of Tocopherol‐Type Compounds in Directing Reactions Forming Flavor Compounds in Autoxidizing Fish Oils

Menhaden and cod liver oils without additives or containing either α‐tocopherol (670 ppm) or Trolox C (1000 ppm) with or without copper (II) cations (20 ppm) were oxidized under air at 65‡C, and their headspace volatiles were quantitatively measured by capillary gas chromatography. Samples prepared without additives contained very little l,5‐octadien‐3‐one. Fish oils with Trolox C had distinct metallic, vinyl‐ketone aromas, while those with a‐tocopherol exhibited extremely fishy, cod liver‐like aromas. High levels of 1,5‐octadien‐3‐one and 1,5‐octadien‐3‐ol and moderate levels of 2,4,7‐decatrienals were found in samples with Trolox C, while moderate levels of the 8‐carbon compounds and high levels of the 2,4,7‐decatrienals were present in the α‐tocopherol samples. Copper (II) greatly accelerated the overall rate of oxidation in samples, and in the presence of Trolox C it induced the formation of very high levels of 1,5‐octadien‐3‐ol.