High-Throughput Raman Chemical Imaging for Rapid Evaluation of Food Safety and Quality

Abstract

Abstract. High-throughput macro-scale Raman chemical imaging was realized on a newly developed line-scan hyperspectral system. The system utilizes a custom-designed 785 nm line laser with maximum power of 5 W as an excitation source. A 24 cm × 1 mm excitation line is normally projected on the sample surface using a 45° dichroic beamsplitter. A detection module consisting of a dispersive imaging spectrograph and a CCD camera is used to acquire Raman signals along the laser line. A motorized positioning table moves the samples transversely through the laser line, and hyperspectral data are obtained using a pushbroom method. System software was developed using LabVIEW to fulfill various functions such as parameter setting, data transfer, and image processing. The system covers a Raman shift range of -691.5 to 2841.2 cm-1 with a spectral resolution of 14 cm-1. The system can collect spatial information requiring either large instantaneous field of view (e.g., 23 cm) or high spatial resolution (e.g., 0.07 mm). The system performance was demonstrated by an example application for authenticating flour. The system acquired a 320 × 250 × 1024 hypercube (80,000 spectra) from three powder samples placed in three Petri dishes (two with a diameter of 47 mm and the other 90 mm) in 9 min. Azodicarbonamide particles mixed in unbleached flour can be detected based on the chemical image generated using a simple image classification method. The method and system for high-throughput macro-scale Raman chemical imaging is promising to inspect other food and agricultural products for safety and quality evaluation.