Determination of Synthetic Food Colorants in Powder Beverage Samples by On-line HPLC–Cupric Reducing Antioxidant Capacity (CUPRAC) Assay with Post-Column Detection

Due to the toxic and carcinogenic effects of some synthetic food colorants, their utilization is limited by food and health regulations. Synthetic colorants are preferred for their stability and low cost in food processing but their misuse may cause health hazards. The aim of this study is to determine food colorants by fast, accurate and applicable methods and inform consumers about the limitations of these substances. Thus, spectrophotometric CUPRAC (cupric ion reducing antioxidant capacity) assay was adapted for the determination of synthetic food colorants so as to define PECC (ponceau 4R equivalent colorant content) coefficients for the calculation of total colorant content of powder beverage samples. The PECC coefficients of the tested colorants were found in the following order: PECCerythrosine > PECCsunsetyellow > PECCtartrazine > PECCindigocarmine. HPLC and on-line HPLC derivatization techniques were developed for synthetic colorants. Total colorant content of synthetic and real (orange and rosehip powder beverage) samples were found and critically compared with the use of three methods, namely spectrophotometric CUPRAC, HPLC (with CUPRAC calculation) and on-line HPLC–post column CUPRAC assays. On-line HPLC–CUPRAC assay yielded low detection limits for colorants. Statistical analyses of the findings of these three methods using the two-way ANOVA test proved that the developed methods for determining synthetic food colorants are accurate, diversely applicable, and well-correlating.