Determination of irradiation histories of raw beef livers using liquid chromatography–tandem mass spectrometry of 5,6-dihydrothymidine

• Irradiation history of raw beef liver was determined by LC–MS/MS analysis of DHdThd.
• DHdThd was specifically formed from thymidine moiety by irradiation.
• DHdThd would be a suitable marker of the irradiation history of raw beef livers.
• The method’s wide applicability and robustness.
• DHdThd, 5,6-dihydrothymindine.

A method for detecting irradiation histories of raw beef livers was developed by measuring 5,6-dihydrothymidine (DHdThd) using liquid chromatography–tandem mass spectrometry (LC–MS/MS). Liver DNA was extracted using phenol–chloroform extraction followed by precipitation in 50% ethanol. DNA was then enzymatically digested and nucleosides were purified using an OASIS MCX column. DHdThd and thymidine (dThd) contents of resulting test solutions were analyzed using LC–MS/MS. DHdThd was detected specifically after γ-irradiation. Concentration ratios of DHdThd to dThd in the test solutions increased dose-dependently after irradiation at 1.0–11.3 kGy, which included the practical dose for sterilization of 2–7 kGy. Dose–response curves from beef livers of individual animals almost overlapped. Thus, this method is a candidate for the detection of irradiation histories of foods from which DNA can be extracted.