Comparison of volatile compounds formed by autoxidation and photosensitized oxidation of cod liver oil in emulsion systems

Volatile compounds formed by photosensitized oxidation and autoxidation of cod liver oil were compared. A 5-mL portion of oil-in-water emulsion (10% oil, 1 % Tween 20 and 0.1 mM of rose bengal or 0.1 mM of ferrous chloride) was sealed into a 50-mL crimp top vial. The vial with added rose bengal was exposed to a 100-watt tungsten bulb (6000 lux) in an oven at 40 degrees C, while the vial with added ferrous chloride was wrapped in aluminum foil to shield light and kept in the same oven. Volatiles in the headspace of the vials were collected by solid phase microextraction technique and analyzed with a gas chromatography-flame ionization detector and a gas chromatography - mass spectrometry. Approximately 51 kinds of volatiles were identified from oxidation of cod liver oil. All the volatiles identified in the sample with added rose bengal were identified in the sample with added ferrous chloride, however, tremendous differences of their relative ratios were found, which probably is useful to explain the flavor differences between sun-dried seafood and mechanical-dried seafood. The formation mechanisms of certain volatiles were proposed.