Raman spectral imaging technique on detection of melamine in skim milk powder

Authors: Chao, Kuanglin - Kevin Chao; DHAKAL, SAGAR - Us Forest Service (FS); Qin, Jianwei - Tony Qin; Kim, Moon

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 6/20/2016
Publication Date: 7/18/2016
Citation: Chao, K., Dhakal, S., Qin, J., Kim, M.S. 2016. Raman spectral imaging technique on detection of melamine in skim milk powder. ASABE Annual International Meeting. ASABE Paper No. 162455818. American Society of Agricultural Biologists and Engineers, St. Joseph, MI.

Interpretive Summary: The consumption of food products contaminated by unsafe chemical adulterants, such as melamine in milk products, has been shown capable of causing illness and even death. Such incidents have illustrated an urgent need for rapid and non-destructive methods to screen foods for chemical adulterants. Qualitative detection of adulterants such as melamine in milk has been demonstrated using Raman spectroscopic methods, but rapid and non-destructive quantitative measurement of such adulterants remains under investigation. Ten dry mixtures of melamine in milk were prepared at concentrations of 0.005%, 0.01%, 0.025%, 0.05%, 0.075%, 0.1%, 0.25%, 0.5%, 0.75%, and 1%- w/w, using an acoustic mixer. A linear relationship was established between the detected melamine concentrations and the actual concentrations of the mixtures, with a correlation coefficient of 0.99. These results provide the basis for a quantitative detection model, using Raman spectral imaging, by which melamine can be detected in milk at concentrations as low as 0.005%. This Raman chemical imaging method can be refined for quantitative measurement of melamine in milk and of chemicals in other food ingredients, for rapid and non-destructive detection of low-concentration adulterants. This method shows promise for use by food processors and regulatory agencies as a non-destructive method for rapid screening of food ingredients for adulterants that pose food safety risks.

Technical Abstract: A point-scan Raman spectral imaging system was used for quantitative detection of melamine in milk powder. A sample depth of 2 mm and corresponding laser intensity of 200 mW were selected after evaluating the penetration of a 785 nm laser through milk powder. Horizontal and vertical spatial resolutions of 0.25 mm and 0.5 mm were selected for effective detection of melamine particles mixed with milk powder. The selected imaging parameters were used to quantitatively detect melamine concentration in milk powder. Ten different concentrations of melamine in milk (0.005%, 0.01%, 0.025%, 0.05%, 0.075%, 0.1%, 0.25%, 0.5%, 0.75%, and 1%- w/w) were prepared by mixing each mixture of melamine and milk powder in an acoustic mixer for 15 minutes, and seven sub-samples of each concentration were imaged. Each sub-sample image was acquired over a 45 mm x 45 mm surface area. It was found that the method developed in this study can detect melamine particles present at concentrations as low as 0.005%. A linear relation was established between the detected melamine concentrations and the actual concentrations of the mixtures, with correlation coefficient of 0.99. The results show that the method developed in this study can be used for non-destructive quantitative prediction of melamine in milk powder to minimum concentration level of 0.005%.