Hyperspectral, Time-Resolved, Fluorescence Imaging System for Large Sample Sizes: Part II. Detection of Fecal Contamination on Spinach Leaves

To reduce the risk of foodborne illnesses resulting from fecal contamination in produce fields, a hyperspectral, line-scan, laser-induced fluorescence imaging system was developed with the goal of eventually incorporating the imaging system into a pre-harvest detection apparatus for fecal contamination. The imaging system includes an intensified, gated camera, a spectral adapter, a 355 nm pulsed laser, and laser expansion optics that produce a line-illumination profile. To validate and test the system, spinach leaves inoculated with dilutions of bovine fecal material were imaged repeatedly using a predefined set of imaging parameters. These images were used to evaluate methods for detecting fecal contamination. Methods investigated included ratio, edge, threshold, and slope detection. Differences in the magnitude of averaged intensities for the spectral range of 450-500 nm for regions within fecal contamination sites and in nearby uncontaminated surface areas suggested that the 450-500 nm waveband would be a good region for use in detection tests. Validation tests that used threshold or slope detection, the 450-500 nm waveband, and that took advantage of the slower fluorescence decay rates of fecal contamination sites relative to uncontaminated surface areas showed almost 100% detection of 1:2, 1:10, and 1:100 dilution sites and over 70% detection of 1:200 dilution sites with essentially zero false positives. These results suggest that the imaging system has potential for development of a commercially viable apparatus for pre-harvest detection of fecal contamination in produce fields and for detection of fecal contamination of leafy green vegetables in general.