Raman Chemical Imaging System for Food Safety and Quality Inspection

Abstract

Raman chemical imaging combines Raman spectroscopy and digital imaging to visualize the 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 system utilizes a 785 nm spectrum-stabilized laser as an excitation source to generate Raman scattering. The detection module consists of a fiber optic probe, a dispersive Raman imaging spectrometer, and a high-performance spectroscopic CCD camera. The imaging system works in a point-scanning mode. A Raman spectrum is obtained at a time for individual positions in the scene. The specimens are carried by a two-axis motorized positioning table. 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 to 2538.1 cm-1 with a spectral resolution of 3.7 cm-1, and an area of 127 127 mm2 with 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 can be used for safety and quality inspection of food and agricultural products.