Purple discoloration of the colon found during autopsy: Identification of betanin, its aglycone and metabolites by liquid chromatography–high-resolution mass spectrometry

• Autopsy finding of purple discoloration of the colon.
• Identification of betanin/betanidin by high resolution MS as cause of discoloration.
• Betanidin glucuronide and sulfate identified as phase II metabolites in urine.

During autopsy of a 38-year-old man the forensic pathologist noted an atypical purple discoloration of the colon membrane. Hypothesis was that the discoloration could have been caused by ingestion of red beetroot. In order to exclude other toxicological causes for this finding and to analytically verify this hypothesis, colon membrane, blood and urine were screened not only for the typical forensically relevant substances but also for the main chromophoric beetroot compounds employing liquid chromatography–high-resolution mass spectrometry (LC–HRMS). Betanin (m/z 551.1495) and its aglycone betanidin (m/z 389.0973) were found in the extracts of colon membrane and urine. Betanin was detected in whole blood, and urinary analysis additionally revealed two metabolites: betanidin glucuronide (m/z 565.1294) and betanidin sulfate (m/z 469.0541) – showing the same fragmentation pattern as betanidin after the characteristic neutral loss of m/z 176.0315 and m/z 79.9554 for glucuronic acid and sulfate, respectively. This is the first time that betacyanins could be analytically confirmed as cause for a purple discoloration of the colon. Urine analysis further revealed that besides betanin itself betanidin phase II metabolites could be detected in human urine.