alpha-tocopherol oxidation in beef and in bovine muscle microsomes

The oxidation of alpha-tocopherol (TH) in beef was analyzed using a stable isotope dilution capillary gas chromatography-mass spectrometry assay. TH d ecreased while alpha-tocopherolquinone (TQ) and 2,3-epoxy-alpha-tocopherolq uinone (TQE(2)) increased in ground longissimus lumborum (LL) and psoas maj or (PM) muscles during storage (P < 0.10). In LL steaks, the relative conce ntrations of TH decreased and TQ and TQE(2) increased in surface samples; c hanges were less dramatic in deep samples. Deuterated alpha-tocopherolhydro quinone (THQ) standard was not recovered and endogenous THQ was not detecte d in meat; THQ was measurable in microsomes isolated from PM and incubated in the presence of 2,2'-azobis(2-amidopropane)HCl (ABAP) or myoglobin. ABAP -challenged microsomes yielded a tocopherol. product profile which favored 5,6-epoxy-alpha-tocopherolquinone (TQE(1)) and TQE(2), while the use of myo globin as prooxidant resulted-in a higher proportion of TQ and THQ. Results demonstrated that concentrations of TK decreased and TQ and TQE(2) increas ed in meat during storage and are consistent with the peroxy-radical scaven ging function of tocopherol.