Alpha-tocopherol oxidation in fish muscle during chilling and frozen storage

The oxidation of alpha-tocopherol (TH) in chilled and frozen fish muscle was determined using high-performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry. TH oxidation byproducts were identified as alpha-tocopherolquinone (TQ), 5,6-epoxy-alpha-tocopherolquinone (TQE1), and 2-3-epoxy-alpha-tocopherolquinone (TQE2). The concentration of TH decreased significantly during storage while those of TQ, TQE1, and TQE2 increased noteworthy. The relative amounts of TH and its oxidized products were significantly related with the extent of oxidation produced in postmortem fish, and the ratio TQ/TH is suggested as an index of oxidative stress in fish muscle. The effect of phenolic antioxidants supplementation on retarding TH oxidation was also studied. Data suggested that the addition of 100 ppm of caffeic acid, hydroxytyrosol, and propyl gallate could regenerate endogenous TH from its oxidized forms resulting in an antioxidant synergy consistent with the reduction of lipid oxidation observed in fish muscle supplemented with phenolic compounds.