Submitted to: Applied Optics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2004
Publication Date: 2/20/2005
Citation: Lefcourt, A.M., Kim, M.S., Chen, Y.R. 2005. Detection of fecal contamination on apples using nonosecond-scale time-resolved imaging of laser induced fluorescence. Applied Optics. 44(7):1160-1170. Interpretive Summary: Apples contaminated with feces have caused illness and death when used to make unpasteurized apple juice or cider. It has been demonstrated that fluorescence imaging can be used to detect feces on apples. In this study, the time courses of fluorescent responses of artificially contaminated apples were measured using a pulsed laser as the light source and a gated, intensified, camera for imaging. Responses at 590, 682, 700 and 730 nm were determined by placing a filter adapter between the lens and camera. It was determined that fluorescence responses of untreated apple surfaces at 682, 700 and 732 nm decayed faster than responses for areas where dairy feces were applied. This information was used to optimize the conditions for detecting feces on apples. For Red Delicious apples, optimal detection of contamination sites utilized images acquired using the 682 nm filter with the camera exposure parameters set so the fluorescence response of the apple surface was largely gone, but there was still some response from the areas treated with feces. For Golden Delicious apples, optimal detection utilized images acquired using the 682 and 590 nm filters, with the camera exposure parameters set so that images were taken during a time period where responses of treated areas exceeded responses of untreated areas in images acquired at 682 nm and responses were visible in images taken at 590 nm. Excellent overall detection resulted when both the 682 nm images and the ratio of the 682 to 590 nm images were analyzed, and the result combined. The results of this research will be of interest to scientists studying fluorescence imaging, and companies interested in developing commercial systems to detect apples contaminated with feces.
Technical Abstract: Detection of apples contaminated with feces is a public health concern. In this study, time resolved imaging of apples artificially contaminated with feces allowed optimization of timing parameters for detection. Dairy feces were applied to Red Delicious apples and Golden Delicious apples. Laser-induced fluorescence responses were imaged using a gated intensified camera. Algorithms to automatically detect contamination were developed iteratively using one half of the apples, and validated by applying the optimized algorithms to the remaining apples. Results show that consideration of the timing of fluorescence responses to pulsed-laser excitation can enhance detection of feces on apples.