# Detection of Azo Dyes in Curry Powder Using a 1064-nm Dispersive Point-Scan Raman System
###### Abstract  
Curry powder is extensively used in Southeast Asian dishes. It has been subject to adulteration by azo dyes. This study used a newly developed 1064 nm dispersive point-scan Raman system for detection of metanil yellow and Sudan-I contamination in curry powder. Curry powder was mixed with metanil yellow and (separately) with Sudan-I, at concentration levels of 1%, 3%, 5%, 7%, and 10% (\(w/w\)). Each sample was packed into a nickel-plated sample container (25 mm \(\times\) 25 mm \(\times\) 1 mm). One Raman spectral image of each sample was acquired across the 25 mm \(\times\) 25 mm surface area. Intensity threshold value was applied to the spectral images of Sudan-I mixtures (at 1593 cm\({}^{-1}\)) and metanil yellow mixtures (at 1147 cm\({}^{-1}\)) to obtain binary detection images. The results show that the number of detected adulterant pixels is linearly correlated with the sample concentration (R\({}^{2}\) = 0.99). The Raman system was further used to obtain a Raman spectral image of a curry powder sample mixed together with Sudan-I and metanil yellow, with each contaminant at equal concentration of 5% (\(w/w\)). The multi-component spectra of the mixture sample were decomposed using self-modeling mixture analysis (SMA) to extract pure component spectra, which were then identified as matching those of Sudan-I and metanil yellow using spectral information divergence (SID) values. The results show that the 1064 nm dispersive Raman system is a potential tool for rapid and nondestructive detection of multiple chemical contaminants in the complex food matrix. R 2018 8564 10.3390/app8040564 13 March 2018 564 10.  
primary ingredients in curry powder, by metanil yellow and Sudan-I color dyes have increased the risk of chemical contamination in curry powder [1; 2; 3]. Metanil yellow (C\({}_{18}\)H\({}_{14}\)N\({}_{3}\)NaO\({}_{3}\)S) and Sudan-I (C\({}_{16}\)H\({}_{12}\)N\({}_{2}\)O) are azo compounds. There are over 3000 azo compounds that account for 65% of the commercial dye market [4]. Azo dyes which are used as synthetic organic colorants are characterized by chromophoric azo groups (-N=N) [4]. Azo dyes reduce to form aromatic amines under anaerobic condition and pose a carcinogenic risk to human health. Metanil yellow is toxicologically classified as a CII category by the Food and Agriculture Organization of the United Nations [5]. Due to its similar color appearance to turmeric, it is often mixed with turmeric [6]. Long-term consumption of metanil yellow causes neurotoxicity [7], hepatocellular carcinoma [8], tumor development [9], deleterious effect on gastrin mucin [10], and lymphocytic leukemia [11]. Sudan-I is a non-ionic fat-soluble azo compound [12], used as color dye to color waxes, oils, petrol, plastics, printing inks, shoes, and polishes. Sudan-I is carcinogenic to humans [13]. It has been classified as a category III carcinogen by the International Agency for Research on Cancer [14]. Due to the low cost, wide availability, and similar color appearance of Sudan-I to spice powders like chili and paprika, it is illegally used as a food color additive [12; 15; 16]. Several studies are reported for detection of chemical contamination in spice powders. Conventional analytical methods such as high-performance liquid chromatography (HPLC) [17; 18], polymerase chain reaction [19], and high performance capillary electrophoresis [20] are used for detection of chemical contaminants in chili and turmeric. Color dyes contamination in chili powder and paste was determined using HPLC-electrospray ionization tandem mass spectrometry [21]. [PERSON] et al. (2008) used a two-directional HPLC method for detection of curcumin, metanil yellow, and Sudan dye in turmeric, chili, and curry powder [22]. Although these methods have high accuracy, factors including high operational costs, requirement for skilled personnel, complicated sample preparation procedure, solvent disposal, and protracted sampling time limit their field application for rapid and non-destructive detection for food safety and quality evaluation.