Consideration of fluorescence properties for the direct determination of erythrosine in saffron in the presence of other synthetic dyes

Abstract

Direct selective detection of erythrosine in saffron in the presence of other synthetic dyes considers its fluorescence at 532 nm excitation/548 nm emission. Saffron pre-treatment was according to the ISO 3632-2 trade standard test methods. On account of calculated quantum yield values, none of the yellow dyes is expected to interfere. Among red ones, reservations about allura red AC, azorubine and red 2G were not verified by experimentation, signifying excellent method specificity. Detection and quantification limits (0.56 and 1.70 nM) were of the same magnitude as those reported in the literature after chromatographic separation of erythrosine. The percentage recovery from spiked saffron samples ranging from 63 to 141 was acceptable for residue levels in foods. The matrix effect from crocins (saffron pigments) was evidenced only at a lower spiking level (0.02  mg kg⁻¹). The minimum required performance limit (MRPL) was 0.04 mg kg⁻¹, indicating that the method is appropriate for determining traces of erythrosine in saffron. The approach offers improved sensitivity (by three orders of magnitude) and specificity than the direct spectrophotometric detection of certain synthetic dyes in saffron and deserves attention by the ISO Technical Committee for ‘Herbs, culinary spices and condiments’.

Keywords:

• screening assays
• regulations
• authenticity
• colours

Acknowledgements

Mrs K. Tsiogka, undergraduate student, is acknowledged for her participation in the recovery study. The authors also thank the unknown reviewers for useful remarks.