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Title: Raman chemical imaging system for food safety and quality inspection

item QIN, JIANWEI - University Of Maryland
item Chao, Kuanglin - Kevin Chao
item Kim, Moon

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2010
Publication Date: 12/10/2010
Citation: Qin, J., Chao, K., Kim, M.S. 2010. Raman chemical imaging system for food safety and quality inspection. Transactions of the ASABE. 53(6):1873-1882.

Interpretive Summary: Recent foodborne illness outbreaks have brought new challenges for monitoring food ingredients and products during processing operations. Advanced sensing technologies that can effectively and efficiently inspect for food safety and quality would reduce the risk of unsafe food for consumers and enhance the competitiveness and profitability of the food industry. In this study, a benchtop point-scanning Raman chemical imaging system was designed and developed for food safety and quality research. The system is able to acquire hyperspectral Raman images in a Raman shift region from 102.2 to 2538.1 cm-1 with a spectral resolution of 3.7 cm-1 and a spatial resolution as high as 0.1 mm. Raman scattering signals are generated using a 785 nm laser excitation source, and collected by a Raman sensing module consisting of a detection probe, a Raman imaging spectrometer, and a camera. A two-axis motorized positioning table moves samples in two perpendicular directions as the Raman spectral data are collected from each spatial point in the scene. Spectral calibration was performed based on two standard chemicals (polystyrene and naphthalene) with known Raman shift wavenumbers. A standard resolution test chart was used for spatial calibration. An example application of detecting melamine particles in dry milk demonstrated that the Raman chemical imaging technique is highly sensitive and can identify specific chemicals at low concentrations. The Raman chemical imaging system developed in this study is a versatile platform capable of using Raman scattering information to map spatial distribution of constituents of interest in complex food systems. The system will be useful to other practical applications (qualitative and/or quantitative) in the area of food safety and quality inspection.

Technical Abstract: Raman chemical imaging technique combines Raman spectroscopy and digital imaging to visualize composition and structure of a target, and it offers great potential for food safety and quality research. In this study, a laboratory-based Raman chemical imaging platform was designed and developed. The imaging system utilizes a 785 nm spectrum-stabilized laser as an excitation source to generate Raman scattering. The detection module mainly consists of a fiber optic Raman probe, a reflection grating-based Raman imaging spectrometer, and a high performance spectroscopic CCD camera. The imaging system works in a point-scanning mode. A Raman spectrum is obtained one at a time for individual positions in the scene. The specimens are carried by a two-axis motorized positioning table, and hyperspectral image data are accumulated as the samples are moved along two spatial dimensions. The parameterization and data-transfer interface software was developed using LabVIEW. Spectral and spatial calibration procedures are presented. The system covers a Raman shift range of 102.2-2538.1 cm-1 with a spectral resolution of 3.7 cm-1 and a spatial resolution as high as 0.1 mm. Performance of the system was demonstrated by an example application on detection of melamine in dry milk. Melamine was mixed into dry milk with concentrations (w/w) ranging from 0.2% to 10.0%. The system was able to create Raman chemical images that can be used to visualize quantity and spatial distribution of melamine particles in the mixtures. The developed system is versatile, and it will be used for safety and quality inspection of food and agricultural products.