3.5. Packaging film biofilm
SEM images were taken of the packaging film touching the lean
portion of the pork chops on each sample day to document the biofilm
formation on the packaging film throughout the storage period. The first
noticeable development of the biofilm was on day 5, as illustrated by
Fig. 7. This SEM image (Fig. 7) shows a protein layer deposited on the
packaging film that comes from the purge and from touching the lean
portion of the pork chops. There is also a smooth globular sphere,
which is a fat globule, so fat was deposited as well. On day 15, some
spoilage bacteria were evident, embedded into the biofilm matrix. The
biofilm also showed a distinct two layer appearance (Fig. 8), and the
black line in the image shows the approximate division of these two
layers. This two layer biofilm consists of the protein layer seen on day
5 covered by the biofilm matrix formed by the spoilage bacteria (black
arrow). This matrix formed by the bacteria is more structured than
the protein layer and has a “honeycomb” appearance. Also in Fig. 8,
the black background is the plastic of the packaging film, which the
biofilm has pulled away from during SEM sample preparation. On day
30, more spoilage bacteria were evident, embedded in the biofilm, as
shown by the arrows pointing to the smooth rod-shaped objects
(Fig. 9). This is consistent with more spoilage bacteria present overall
in the package, so more would be embedded in the packaging film. On
day 45 and 60, the biofilm appeared the same, with more bacteria
embedded in the biofilm and the biofilm filling up with fat deposits
and loose protein, as shown by Fig. 10. More spoilage bacteria were
embedded in the biofilm because of the larger concentration of spoilage
bacteria present, upwards to log10 8 CFU/cm2
. Although relatively few
bacteria are evident in the biofilm, most may not be visible because
they are embedded beneath the surface. The biofilm on day 45 and
60 had more fat deposits filling in the honeycomb structure of the
biofilm as well as another protein layer being deposited on top of the
biofilm matrix (Fig. 10). This second protein layer was starting to occur
because the pork chops inside the package were decomposing due to
the extensive microbial spoilage occurring. This microbial spoilage
would have freed up some protein from the pork chops and allowing it
to settle on top of the biofilm layer. The protein could also come from
the purge because as the storage period approached 60 days, the purge
proteins started to precipitate. This protein precipitation could have also
contributed to the second protein layer.