Analytical methods for detection of Sudan dyes in food: a critical review of sample preparation, instrumental techniques and global surveillance data (2010–2025)

Food adulteration with illegal synthetic dyes poses a persistent global public health threat, with Sudan dyes – lipophilic azo compounds originally developed for industrial applications – representing the most prevalent and toxicologically significant class of illicit colourants in the food supply. Following a structured search of five bibliographic databases and regulatory grey literature under pre-specified eligibility criteria, this critical review synthesises analytical methodologies, global occurrence patterns, and regulatory frameworks surrounding Sudan dyes and related illegal colourants published from 2010 to 2025. Contemporary liquid chromatography-tandem mass spectrometry methods achieve detection limits in the sub-µg/kg range, while emerging high-resolution mass spectrometry and ambient ionisation platforms offer complementary capabilities for non-targeted screening. Critical appraisal of global surveillance data reveals persistent contamination of chilli-based products and edible oils, with marked geographic heterogeneity in prevalence rates and concentration ranges spanning seven orders of magnitude – from trace-level cross-contamination to gross adulteration at g/kg levels. Notably, the detection of Sudan dye variants beyond the classical Sudan I–IV series, including Sudan Red B, Sudan Yellow, and Sudan Black B, indicates evolving adulterant selection by fraudsters responding to enhanced regulatory surveillance. This review identifies critical knowledge gaps and proposes future directions encompassing expanded analytical target panels, enhanced non-targeted screening capabilities, and field-deployable technologies to strengthen food supply chain integrity.