Submitted to: Applied Optics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2003
Publication Date: January 1, 2003
Citation: LEFCOURT, A.M., KIM, M.S., CHEN, Y.R. AUTOMATED DETECTION OF FECAL CONTAMINATION OF APPLES BY MULTISPECTRAL LASER-INDUCED FLUORESCENCE IMAGING. APPLIED OPTICS. 2003. Interpretive Summary: Feces from dairy cows and deer are suspected of being sources of contamination of apples by disease causing organisms. Contaminated apples have caused illness and death when used to make unpasteurized apple juice or cider. Animal feces contains chemical compounds such as chlorophyll that can be detected by the fluorescence responses of these compounds to ultraviolet (UV) light. In this study, a pulsed laser was used as the UV light source and fluorescence responses were measured using a gated-intensified camera. To test the sensitivity of this system, dilutions of dairy cow feces, deer feces, and dairy feces from a fallow pasture were applied to red delicious apples. Fluorescence responses were determined 1 d and 7 d after application, and then after washing and brushing the apples. On day 1, over 85% of dairy feces contamination spots were successfully detected for the 1:2, 1:20, and 1:200 dilutions; for deer, essentially all contamination spots were detected, even the 1:2000 dilution spots. The 1:200 dilution contamination spots contained about 15 ng of solid material. Following washing and brushing, fecal contamination could still be detected for all dilutions of deer feces and for many of the other feces sources. Washing and brushing had the greatest effect on detection of contamination with pasture feces; 100% of the 1:2 dilution spots could still be detected while none of the 1:200 dilution spots could be detected. These findings demonstrate that the multispectral laser-induced fluorescence imaging system is a very sensitive method for detecting fecal contamination on apples. Results suggest that this technology could potentially be incorporated into commercial systems to detect fecal contamination in food processing plants and, more specifically, into systems to remove fecal contaminated apples prior to juice making or selection of apples for the fresh fruit market; the potential beneficiaries are food producers and consumers.
Technical Abstract: Feces from dairy cows and deer are suspected of being sources of microbiological contamination of apples by disease causing organisms such as E.coli:O157. Contaminated apples have caused illness and death when used to make unpasteurized apple juice or cider. The potential for using fluorescent compounds in feces as markers for fecal contamination has been demonstrated. To test the ability and sensitivity of laser-induced fluorescence to detect fecal contamination of apples, serial dilutions of feces from dairy cows, deer, and a pasture formerly used to house dairy cows were applied to red delicious apples. Fluorescence responses were determined 1 d and 7 d after application using a laser induced fluorescence imaging system with a gated-intensified camera. Subsequently, responses were determined after washing, or washing and brushing, the apples. At day 1, over 85% of contaminated spots were successfully detected for 1:2, 1:20, and 1:200 dilutions and, for deer, also at the 1:2000 dilution. The 1:200 dilutions, as applied, corresponded to 15 ng of dry matter or less. Detection percentages were similar at 7d. Following washing and brushing, fecal contamination could still be detected for all dilutions of deer feces and for many of the other feces sources. Washing and brushing had the greatest effect on detection of contamination with pasture feces where detection percentages were 100%, 30%, and 0% for 1:2, 1:20, and 1:200 dilutions, respectively. Thus, multispectral laser-induced fluorescence was found to be a very sensitive method for detecting fecal contamination on apples. Results suggest that this technique may be an appropriate basis for development of commercial system for detecting fecal contamination of apples.