food quality. Among such processes, adequate packaging is a fundamental
factor in the conservation and marketing phases. Thus, packaging
plays a prominent role in maintaining food quality. Antimicrobial
films and coatings have vitalized the concept of active packaging and
have been developed to reduce, inhibit or delay the growth ofmicroorganisms
on the surface of foods in contact with the packaged product
[143,144].
In most fresh or processed foods,microbial contamination occurs at a
higher intensity on the food surface, thus requiring an effectivemicrobial
growth control. Traditionally, antimicrobial agents are added directly to
the foods, but their activity may be inhibited by many substances in
the food itself, diminishing their efficiency. In such cases, the use of antimicrobial
films or coatings can be more efficient than adding antimicrobial
agents directly to the food since these may selectively and gradually
migrate from the package onto the surface of the food, thereby high concentrations
being maintained when most necessary [114].
L. monocytogenes, a Gram-positive rod, is a bacterium that can
cause illness in a variety of food products [145]. One food product of
great concern is the refrigerated, ready-to-eat (RTE) foods contaminated
with L. monocytogenes [146]. Eating foods contaminated with
L. monocytogenes normally causes the disease listeriosis which is
more serious for elderly adults and adults with compromised immune
systems and can cause meningitis [147]. In pregnant women,
the disease may cause spontaneous abortions or stillborn babies.
Greenwood [147] has studied the antimicrobial effect of chitosan, as
an edible film, that was dissolved in lactic acid or acetic acid against
L. monocytogenes on RTE roast beef. Chitosan with low and high molecular
weight (MW) of (4.7×105 g/mol) and (1.1×106 g/mol)
were used to test the molecular weight effect on the antimicrobial capacity.
This study showed that the acetic acid chitosan coating was
more effective in reducing L. monocytogenes counts than the lactic
acid chitosan coating. The study indicated also that chitosan coatings
could be used to control L. monocytogenes on the surface of RTE roast
beef. However, it has been found that L. monocytogenes was able to
grow on the surface of the RTE roast beef regardless of the chitosan
treatments used. Coma et al. [13] also observed the ability of
L. monocytogenes to grow on the surface of cheese regardless of chitosan
treatments. This could be due to the decreased antimicrobial activity
of chitosan films over time as a consequence of the decreased
availability of amino groups on chitosan [147]. The L. monocytogenes
strain used during this study was able to grow on the surface of the
RTE roast beef product. The initial level of 6.50 log CFU/g increased
to over 10 log CFU/g on the control samples at day 21 while samples
dipped in chitosan have a count of 7.4–7.9 for high and low molecular
weight chitosan respectively. The data indicated an improvement of