Identification of the monobrominated derivative of Acid Red 52 (Food Red No. 106) in pickled vegetables

ABSTRACT

Two unknown dyes (purple and purplish-red) were detected by TLC in two pickled vegetable (sakura-zuke daikon) samples containing Acid Red 52 (AR) and New Coccine as food colorants. HPLC with diode-array detection and LC/MS analyses suggested that the purple dye is monobrominated AR and the purplish-red dye is its N-desethyl derivative, which would be generated mainly during sample preparation. For the identification of the purple dye, a reference compound was prepared by bromination of AR followed by isolation of the monobrominated AR, the structure of which was elucidated as 4′-brominated AR (4′BrAR) by LC/ToF-MS and ¹H-NMR spectroscopy. The purple dye was confirmed as 4′BrAR by comparison of its retention time, ultraviolet-visible spectrum and mass spectrum with those of the prepared reference compound. To our knowledge, this is the first report of the detection of 4′BrAR in foods.

KEYWORDS:

• Acid Red 52
• Food Red No. 106
• unknown dye
• monobrominated derivative

Acknowledgement

The authors thank Haruko Sekido of Kanagawa Prefecture Institute of Public Health for her kind support in LC/TOF-MS analysis.

Disclosure statement

No potential conflict of interest was reported by the author(s).