Mutagenicity of the food colour brown FK and constituents in Salmonella typhimurium.

The food colour Brown FK (EEC Serial No. 124) is a mixture of p-sulphophenylazo derivatives of m-toluylenediamine and m-phenylenediamine and is used in the UK for colouring kippers. Brown FK and its constituents were assayed for mutagenicity in Salmonella typhimurium TA 1535, TA 1537 and TA 1538. Samples of Brown FK from three manufacturers were mutagenic in TA 1538 (framshift mutant) when activated by a rat-liver supernatant fraction. Mutagenicity was linearly dose-dependent in the range of 0--3 mg/plate with activities ranging from 22 to 50 times the spontaneous mutation frequency. One sample of Brown FK was mutagenic in the absence of metabolic activation producing a 16-fold increase in mutation at 4 mg/plate. Two major constituents of Brown FK, 2,4-diamino-5-(p-sulphophenylazo)-toluene (I) and 1,3-diamino-4-(p-sulphophenylazo)benzend (II), each present at about 18% in the complete colour, were mutagenic in TA 1538. Mutagenicity was linearly dose-related in the range 0--1 mumol/plate, with slopes of 0.35 mutants/nmol for compound I and 1.5 mutants/nmol for compound II. This activity was dependent on metabolic activation. Four other major constituents, (di- and tri-substituted diamines) were inactive, as was sulphanilic acid, the major excretion product of Brown FK. The mutagenicity of Brown FK could be largely accounted for by the combined effects of compounds I and II. Earlier studies showed that compounds I and II were responsible for the acute myotoxic effects seen when Brown FK was given per os to rats and pigs. Azoreductive fission of I and II to reactive triamines by gut microflora was thought to be the main metabolic pathway by which Brown FK produced its myotoxic effects, and it is proposed that the mutagenic effects of Brown FK are probably mediated by a similar mechanism.