acquire two data cubes, with and without LED illumination, and to
calculate and display difference images is about 24 s plus any added
display time for difference images.
The autofluorescence of HDPE from 450 to about 525 nm seen
in Fig. 12 was noted in a prior laboratory study of produce residues
(Wiederoder et al., 2012). As was discussed in this earlier study,
this autofluorescence-based results in the melon pieces appearing
black at 475 and 520 nm (Fig. 11). Under ambient fluorescent lighting,
the contrast at 475 nm was greater than the contrast at
675 nm. This difference in contrast suggests that scanning could
be done at a greater distance while using imaging at 475 nm to
bringing attention to possible small pieces of produce residue.
The camera head could then be brought closer to the suspected
anomaly to allow examination at 675 nm.
The relatively brighter lines in images at 475 and 520 nm reflect
cutting board use and are most likely knife cuts (Fig. 11).
The contrast of these lines is greater in images at 520 nm.
Although these lines do not necessarily represent a direct food
safety concern, areas of concentrated use might be good sites
for ATP testing.
The melon pieces were easily identifiable at 675 nm, even when
ambient fluorescent lights were on (Fig. 11). The juice trails evident
in the 675 mm images were created when melon pieces were
positioned in a row using a knife tip. The trails were not visible
to the naked eye in the absence of violet excitation, and were only
faintly visible with violet excitation when the ambient lights were
turned off. The pieces were cut on a different cutting board, transferredtransferred
to a paper cup, and then placed on the imaging cutting board
by lifting them out of the cup. Thus, the juices shown in images are
primarily the result of ‘‘damage’’ resulting from dragging the pieces
across the cutting board surface. The ability to see the trails in the
675 nm images is indicative of the sensitivity of the imaging device.