Determination of Reactive Dyes in Coloring Foodstuff, Fruit Juice Concentrates, and Meat Products by Reductive Azo-Bond Cleavage and LC-ESI-MS/MS Analysis

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Visually appealing foods are often associated by consumers with subjective quality features, such as freshness, palatability, and shelf life. In the past, there have been repeated violations in which regulations on the use of pigments in food were ignored and/or unauthorized or toxic dyes (e.g., Sudan red in paprika powder) were added. Most recently, adulterations by using reactive dyes from the textile sector have been reported. These included, among others, colored spice preparations for use in meat products (e.g., for sausages and meat products), which were advertised to contain natural plant-derived pigments mainly consisting of betalains and/or anthocyanins. In contrast to natural dyes, reactive dyes are very stable toward extreme pH values, heat, and light. Due to their chemical properties, reactive dyes cannot be detected by classical dye analysis as they may be covalently bound to the food matrix. Methods for the analysis of matrix-bound reactive dyes are therefore required. In this study, a reductive cleavage method of bound textile dyes in different food matrices (spice mixtures, fruit juices, and scalded sausages) and the detection of characteristic cleavage products after enrichment by solid phase extraction (SPE) and liquid chromatography-electrospray ionization-tandem mass spectrometric (LC-ESI-MS/MS) analysis is reported. In addition, 13 suspicious samples provided by project partners were analyzed using the newly developed LC-ESI-MS method.