1a. Objectives (from AD-416):
To develop line-scan technology and design and construct macro-scale Raman chemical imaging instrumentation, and to develop methodology for macro-scale Raman imaging detection of contaminants and adulterants for food samples and food ingredients.
1b. Approach (from AD-416):
Develop optical method to create laser-line illumination from a 785nm laser source. Implement Raman spectrograph with electron-multiplying charge-coupled device camera. Incorporate line laser and detector into a portable instrument for macro-scale Raman imaging of samples up to 10x20 cm in size. Develop computer programs for real-time data acquisition, data analysis, and classification. Perform system calibration/validation. Investigate contaminant and adulterant detection for food samples such as authentication of dry milk powder or other food ingredients, and detection of pesticide residues on fruits and leafy green vegetables.
3. Progress Report:
Raman chemical imaging was investigated for the detection and visualization of contaminants in dry milk powder, and Raman spectroscopy was investigated for quantitative assessment of contaminants in liquid milk samples. The contaminants used in this study were melamine, ammonium sulfate, dicyandiamide, and urea, which are chemicals that can dupe the standard nitrogen-testing method used to estimate protein content in foods. Milk-contaminant mixtures were prepared with contaminant concentrations between 0.2% and 10.0% in the dry milk powder samples, and between 0.04% and 10.0% in liquid milk samples. Raman chemical images of the dry samples were analyzed and used to create image maps that demonstrated the detection of the contaminants with visualization of the spatial distribution of the contaminant particles within the sample mixtures. Raman spectral analysis of the liquid samples showed linear relationships existing between Raman intensities and contaminant concentration, demonstrating the feasibility of quantitative assessment. Raman chemical imaging and spectroscopy techniques therefore may be considered promising methods for non-destructive screening of food ingredients for adulterants.