| `Visual inspection of produce fields for signs of fecal contamination and animal intrusion prior to harvest is a currently prescribed method for reducing risk of foodborne illnesses. This report details the continuing development of a fluorescence imaging system to augment human visual inspection. Previous research established that chlorophyll and related compounds, commonly found in feces and injury sites on plants, can be detected using fluorescent responses to UV excitation. In this study, a time-resolved multispectral imaging system was modified to allow hyperspectral line-scan imaging of fluorescent responses to 355-nm pulsed-laser excitation. Addition of a spectral adapter allowed acquisition of line images representing one spatial dimension with full spectral information for each spatial pixel location. Full-object images can be created by concatenating sequential line-scan images. For line-scan imaging, full-object illumination is inefficient. To better fit the illumination to the line-scan imaging field, laser line-expansion was achieved using a Powell lens. Illumination efficiency was 28.5% using the Powell lens compared to 3.0% using simple optical expansion. To test the modified system, spinach was inoculated with 1:2, 1:10, 1:100, and 1:200 dilutions of bovine manure. Using detection based on visual observation, a 100% detection rate was found for all dilutions. Automated detection rates using estimates of fluorescent decay were 100%, 100%, 100%, and 82 % for the 1:2, 1:10, 1:100, and 1:200 dilutions, respectively. These results suggest this technology has potential for the development of a commercial system for pre-harvest detection of fecal contamination and signs of animal intrusion. |
