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Illegal dyes in food and spices: screening method for 19 dyes

A general screening method which extends the 2006 GC screening method to 19 synthetic dyes has been published

A new paper in the Journal of the Association of Public Analysts describes a general screening method for the detection of 19 synthetic dyes in 5 different food products.

Synthetic dyes have been widely used as industrial colouring agents. However if used in food, adverse effects on health can ensue. Consequently the use of most synthetic dyes in food products is now forbidden in Europe. To protect consumers and legitimate businesses, food products must be monitored and tested regularly for assurance that they are free of illegal dyes, which requires reliable methods of analysis.

Since the emergence in 2003 of Sudan I as a contaminant in chilli powder, the Government Chemist has had an interest in illegal dyes. In 2006 the Government Chemist developed and released a method for the quantitative determination of six illegal dyes in chilli and paprika powder.

In this paper by Gray et al (JAPA Online (2016) 44 018-039), key aspects of the 2006 UV-Visible method are described and a more general screening method is proposed. The method, using acetone extraction and reverse-phase high performance liquid chromatography combined with UV-visible detection, was investigated for the detection of 23 dyes most often implicated in food recalls. The screening method was successfully applied to 19 of these dyes in five food products: chilli powder, canned chicken in a curry sauce, fennel, palm oil and paprika. Recovery, linearity and within-day precision data are reported.

Turmeric proved to be a very challenging matrix for which the proposed general screening method in its present format is not applicable. Furthermore, for the small number of problematic dyes and for further confirmation for those with close retention times, an alternative mass spectrometric detection method is recommended.