# Detection of Azo Dyes in Curry Powder Using a 1064-nm Dispersive Point-Scan Raman System
###### Abstract
Fourier transform Raman (FT-Raman) spectroscopy using a 1064 nm laser source and a commercial Raman spectroscopic system (using 514 nm and 785 nm laser source), coupled with a surface-enhancement method are used for detecting chemical contamination in food spices [23]. [PERSON] et al. (2016) used FT-Raman for detection of metanil yellow contamination in turmeric [1]. Turmeric and metanil yellow were mixed in de-ionized water to obtain a homogenously mixed sample. The liquid sample was filled in a NMR tube, held and adjusted in the sample compartment to focus the laser light on the sample for spectral measurement. [PERSON] et al. (2010) used a surface-enhancement Raman spectroscopic method to detect Sudan-I contamination in chili [24]. In these systems, the sample is adjusted to focus the incident light on the sample surface for spectral measurement from selected spots. The need for sample adjustment for each subsequent measurement precludes these systems measuring a large surface area of the sample. These techniques, being spot measurement, are useful for evaluation of homogenous samples only. Detection of chemical contaminants in food powders requires spectral measurement of the entire surface area of the sample. The hyperspectral imaging technique is used for collection of spectral images of large samples. A line-scan 785 nm Raman chemical imaging system was developed for evaluation of food safety and quality [25]. The system has been used for authentication of food powders by detection of chemical contaminants such as azodicarbonamide in flour [25]; melamine, benzoyl peroxide, and maleic anhydride in skim milk powder, wheat flour, and corn starch [26]; and urea in skim milk powder [27]. However, pigmented food samples such as curry powder, turmeric, and paprika and chemical contaminants such as metanil yellow and Sudan dye emit high fluorescence. The 785 nm Raman chemical imaging system cannot be used to measure these samples. It is a challenge for currently available Raman systems to authenticate curry powder contaminated with azo dyes such as Sudan-I and metanil yellow. This study used a newly developed 1064 nm dispersive Raman system [28] to measure curry powder mixed with Sudan-I and (separately) with metanil yellow at different concentrations for detection of Sudan-I and metanil yellow contamination in curry powder. This study further demonstrates the use of the 1064 nm Raman system for simultaneous detection of multiple contaminants (Sudan-I and metanil yellow) in curry powder. Self-modeling mixture analysis (SMA) was used to decompose the multi-component spectra of the sample mixture and extract pure component spectra of Sudan-I and metanil yellow. The primary objectives of this study are to:  
1. Obtain Raman spectral images of curry powder-metanil yellow, curry powder-Sudan I, and curry powder-metanil yellow--Sudan I samples prepared at different concentrations using the 1064 nm Raman system;
2. Identify the vibrational modes which are effective markers for specific chemical structural features unique to the metanil yellow and Sudan-I and discrete from the curry powder matrix vibrational modes;
3. Detect Sudan-I and metanil yellow contamination in curry powder at different concentrations;
4. Use self-modeling mixture analysis to resolve the multi-component spectra of curry powder-metanil yellow-Sudan I mixture sample into pure component spectra and scores for simultaneous detection of Sudan-I and metanil yellow.