Time-dependent differences in
fluorescence responses of normal surfaces of the fruit or vegetable as opposed to surfaces which are contaminated with
feces, may be used for improved detection of
feces-contaminated
fruits and vegetables. In this process, the surface of a fruit or vegetable which contains a native
chlorophyll is illuminated with a pulse of UV or visible light having a
wavelength effective to elicit
fluorescence of
feces of a
plant consuming animal. The intensity of
fluorescent light emissions from the surface are measured at one or more wavelengths characteristic of the emission spectra of
chlorophyll or its degradation products, at a
nanosecond-scale time period or window which is after the peak emission of the native
chlorophyll of the fruit or vegetable. The presence of fecal
contamination is determined by comparing this measured intensity to a threshold value of the intensity of
fluorescent light emissions for a non-feces contaminated control of the same fruit or vegetable measured at substantially the same conditions, substantially the same said time period, and at substantially the same said wavelengths. A determination that the measured intensity of the
fluorescent light emissions is significantly greater than the threshold value is an indication of the presence of fecal material on the surface of the fruit or vegetable.