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Synthesis and Application of 13C-Labeled 2-Acetyl-4-((1R,2S,3R)-1,2,3,4-tetrahydroxybutyl)imidazole (THI), an Immunosuppressant Observed in Caramel Food Colorings

Elsinghorst, Paul W., Raters, Marion, Dingel, Anna, Fischer, Jochen, Matissek, Reinhard
Journal of agricultural and food chemistry 2013 v.61 no.31 pp. 7494-7499
beers, food coloring, isotope dilution technique, pollutants, rodents, soft drinks, stable isotopes, surveys, toxicity
2-Acetyl-4-((1R,2S,3R)-1,2,3,4-tetrahydroxybutyl)imidazole (THI) is a minor toxic contaminant observed in caramel food colorings and was shown to exert immunosuppressant activity when fed to rodents. Because of this toxicity, maximum levels of THI in caramel food colorings have been defined by international and European authorities. Several reports of THI analysis using external standardization have been published for liquid foods such as beers and soft drinks. However, no suitable internal standard has yet been described allowing THI analysis in more complex samples. In this paper we describe the preparation of a labeled [¹³C₆]THI analogue and its application for the successful validation of the first stable isotope dilution assay (SIDA) of THI in caramel food colorings. A brief survey of THI levels in commercially available caramel class III (E 150c) and IV (E 150d) food colorings is also included, corroborating that THI occurs only in caramel class III food colorings.