Optimal fluorescence excitation and emission bands for detection of fecal contamination

Fecal contamination of food products is a critical health issue. To test the feasibility of the use fluorescent techniques to detect fecal contamination, fluorescence excitation and emission characteristics of fecal matter from cows, deer, swine, chickens, and turkeys in the UV to far-red regions of the spectrum were evaluated. To allow the optimization of the detection of fecal contamination on animal carcasses and cut meats, emission-excitation spectra of the feces were compared with spectra for animal meats. The feedstuffs for the swine, chickens, and turkeys were also analyzed. Excitation at approximately 410 to 420 nm yielded the highest level of fluorescence for both feces and feedstuffs. Emission maxima were in the red region (at 632 nm for chicken feces and at 675 nm for the feces of the other species). The major constituent responsible for emission at 632 nm was tentatively identified as protoporphyrin IX; emission at 675 nm most likely emanates from chlorophyll a or its metabolites. Animal meats emitted strong fluorescence in the blue-green regions, but no emission peaks were observed in the red region for these meats. These results suggest that fluorescence emissions from naturally occurring chlorophyll a and its metabolites are good markers for fecal contamination and that with excitation at 410 to 420 nm, the responses of fecal matter can easily be differentiated from the responses of animal meats. We suggest that the detection of fecal contamination can be enhanced by requiring a minimum chlorophyll a content in the finishing diets of all farm animals.