Anaerobic metabolism of 1-amino-2-naphthol-based azo dyes (Sudan dyes) by human intestinal microflora

Abstract

The rates of metabolism of Sudan I and II and Para Red by human intestinal microflora were high compared to those of Sudan III and IV under anaerobic conditions. Metabolites of the dyes were identified as aniline, 2,4-dimethylaniline, o-toluidine, and 4-nitroaniline through high-performance liquid chromatography and liquid chromatography electrospray ionization tandem mass spectrometry analyses. These data indicate that human intestinal bacteria are able to reduce Sudan dyes to form potentially carcinogenic aromatic amines.

FIG. 1.

Extent of metabolism of Sudan dyes by the human intestinal microflora. The concentrations used were as follows: Sudan I, 10 μg/ml; Sudan II, 10 μg/ml; Sudan III, 0.3 μg/ml; Sudan IV, 0.5 μg/ml; Para Red, 10 μg/ml. Error bars represent the standard deviations of triplicate cultures.

FIG. 2.

Product ion mass spectra of the aniline metabolite from Sudan I (A), the 2,4-dimethylaniline metabolite from Sudan II (B), the aniline metabolite from Sudan III (C), the o-toluidine metabolite from Sudan IV (D), and the p-nitroaniline metabolite from Para Red (E), which were obtained by the incubation of Sudan dyes with the human intestinal microflora.

FIG. 3.

Suggested possible pathway for the reduction of Sudan dyes by the human intestinal microflora. 1-Amino-2-naphthol, 1,4-phenylenediamine, and 2,5-diaminotoluene (in brackets) could not be detected in the extracted samples. Some brown substances in the metabolites of Sudan dyes did not dissolve in the starting buffer for LC/ESI-MS/MS analysis.