dioxide has been shown to inhibit the
growth of Klebsiella pneumoniae and S.
aureus using an agar plate assay.
In a further report, Fonseca et al.
fabricated polylactide modified with
titanium dioxide nanoparticles and
assessed antimicrobial activity by submerging coupons in brain-heart infusion broth inoculated with E. coli, then
illuminated with UV-A. The authors
reported a 94 percent reduction on E.
coli numbers compared with control
cultures, although it was unclear if this
could be attributed to bacteriostatic or
bactericidal activity. A more detailed
study examined the antilisterial properties of biodegradable PLA coatings
modified with titanium dioxide.
35 It was
demonstrated that PLA alone could
support a 2.84 ± 0.10-log CFU reduction of L. monocytogenes when incubated
at 23 °C for 2 hours, although the log
reduction was increased to greater than
4-log CFU when titanium dioxide was
incorporated into the PLA film during
casting and illuminated with UV-A.
The coating was stable in repeated (up
to five) sanitation cycles consisting of
detergent and sodium hypochlorite
N-halamine is a further food-contact
antimicrobial coating gaining interest with the added advantage of being
regenerated by activation with hypochlorite.
36 However, how halamine films
function under commercial processing
conditions remains to be assessed.
The number of product recalls due
to suspected L. monocytogenes contami-
nation is forecast to increase, while our
ability to detect the pathogen outper-
forms our ability to control it. The first
protective coatings were introduced in
the 1990s and have undergone several
generations of development, especially
given innovations in packaging and the
clinical sector. The generation of food-
contact-compatible polymers modified
with antimicrobial agents has strong
potential for Listeria control. The most
successful coatings would probably be
applied as a film following a sanitation
activity as opposed to surfaces being
manufactured with impregnated antimi-
crobials. This is based on cost aspects
in addition to the short-term stability
of impregnated coatings. In this respect,
the biggest knowledge gap that exists
relates to how antimicrobial coatings
perform under commercial conditions.
This and other aspects of antimicrobial
coatings will be explored in the near
Keith Warriner, Ph.D., is a professor in the Department of Food Science at the University of Guelph in
Ontario, Canada. His research covers a broad area of
food safety from emerging pathogens to intervention
technologies, wastewater treatment and antimicrobial
coatings. His main research focus is studying the
interaction of pathogens with fresh produce and developing decontamination methods as an alternative
to postharvest washes. He is the past president of the
Ontario Association for Food Protection and the recipient of the Premier’s Award for Agri-Food Innovation
Excellence along with Paul Moyer of Moyers Apple
Products Inc. In addition to research, he teaches food
microbiology, industrial microbiology and food safety
management at the University of Guelph.
Kayla Murray, M.Sc., is currently a Ph.D.
candidate in the Department of Food Science at the
University of Guelph. She holds a B.Sc. (Hons) in
microbiology and an M.Sc. in food microbiology, both
from the University of Guelph. Her research is studying
the dynamics of microbial populations associated with
biological membrane reactors. She currently holds a
Highly Qualified Personnel scholarship kindly provided
by the Ontario Ministry of Agriculture and Food and
Ministry of Rural Affairs.
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