Food Additives and Contaminants, October 2005; 22(10): 980–987
Effectiveness of antimicrobial food packaging materials
K. COOKSEY
Department of Packaging Science, Clemson University, 229 Poole Ag Center, Box 340320,
Clemson, SC 29634-0370, USA
Abstract
Antimicrobial additives have been used successfully for many years as direct food additives. The literature provides
evidence that some of these additives may be effective as indirect food additives incorporated into food packaging materials.
Antimicrobial food packaging is directed toward the reduction of surface contamination of processed, prepared foods
such as sliced meats and Frankfurter sausages (hot dogs). The use of such packaging materials is not meant to be a substitute
for good sanitation practices, but it should enhance the safety of food as an additional hurdle for the growth of pathogenic
and/or spoilage microorganisms. Studies have focused on establishing methods for coating low-density polyethylene film
or barrier films with methyl cellulose as a carrier for nisin. These films have significantly reduced the presence of
Listeria monocytogenes in solutions and in vacuum packaged hot dogs. Other research has focused on the use of chitosan to
inhibit L. monocytogenes and chlorine dioxide sachets for the reduction of Salmonella on modified atmosphere-packaged
fresh chicken breasts. Overall, antimicrobial packaging shows promise as an effective method for the inhibition of certain
bacteria in foods, but barriers to their commercial implementation continue to exist.
Keywords: Antimicrobial packaging, nisin films, chitosan, chlorine dioxide, modified atmosphere
Introduction
Antimicrobial packaging has been an area of interest
for many years. As research in the area continues,
more systems are showing promise for commercial
application. The concept behind antimicrobial
packaging is to enhance the safety and quality
measures already used by the food industry. It is
not meant as a substitute for good manufacturing
and handling practices, but is meant to serve as an
additional hurdle for bacteria to overcome.
Several conditions should be considered when
designing an antimicrobial packaging system. First,
the regulatory status of the antimicrobial agent is
important. Some antimicrobial systems rely on
diffusion or release of the antimicrobial agent in
order for it to be effective. This would place the
packaging material under the classification of an
indirect food additive and the material would require
review by the US Food and Drug Administration
(FDA) along with similar scrutiny in other countries.
Generally, approval may not be difficult if the
additive has already been effectively used as a direct
Correspondence: K. Cooksey. E-mail: [email protected]
ISSN 0265–203X print/ISSN 1464–5122 online ß 2005 Taylor & Francis
DOI: 10.1080/02652030500246164
food additive as long as migratory concentrations
and conditions of use are addressed. Another issue
is the cost-to-benefit ratio. Some antimicrobial
systems can be effective, but if produced on a large
scale, they might require expenses beyond the
benefits obtained by an extended shelf life or
improvement in quality. Lastly, there are numerous
technical challenges related to coating methods, the
rate of curing, the ease of heat sealing, the effects on
physical and mechanical properties of film, the
effects on colour, the texture or flavour of the food,
and the ability of the antimicrobial agent to
provide effectiveness throughout the package/
product life cycle. The challenges can be daunting,
but as research in the field progresses, there is
promise for many systems to meet these challenges.
A variety of antimicrobial packaging systems
have been reviewed (Kesler and Fennema 1986;
Krochta and De Mulder-Johnston 1997; Han 2000;
Cooksey 2001; Brody 2002). While some films
have incorporated the antimicrobial agent into the
polymer (Siragusa et al. 1999), others have used
Effectiveness of antimicrobial food packaging materials
biopolymer films as effective carriers of antimicrobial
agents (Padgett et al. 1998; Coma et al. 2001). Many
of these biopolymer films are cellulose-based, and
because of their water-soluble nature, they effectively
release additives when combined with foods of
high water content. For example, upon contact,
a cellulose-based matrix degrades and releases the
antimicrobial agent from the matrix to the surface of
the food product resulting in bacterial inhibition.
However, chitosan is a biopolymer with inherent
antimicrobial properties and it does not require a
carrier. It can be used as a coating or cast into films
with good strength and barrier properties (Wiles
2000). Unlike the previous systems mentioned,
vapour-active antimicrobial packaging systems do
not require direct surface contact. Vapour-active
antimicrobial agents include allyl isothiocyanate,
ethanol and chlorine dioxide.
Nisin has ‘Generally Recognized as Safe’ (GRAS)
status in the USA for use in processed cheese
spreads. It is an lantibiotic produced by
Lactobacillus lactis and destroys target cells by incorporating itself into their cytoplasmic membranes,
which leads to a loss of intracellular ions and
disruption of the pH gradient and proton motive
force (Klaenhammer 1993; Breukink and De Kruijff
1999; Jydegaard et al. 2000). The initial step of
the antibacterial action is the binding of nisin
molecules to the cell membrane. Studies have
shown that nisin preferentially binds to membranes
containing anionic lipids. Gram-positive bacteria
generally have higher concentrations of anionic
lipids in their plasma membrane than Gram-negative
bacteria, which may explain the increased antimicrobial activity towards Gram-positive bacteria
(Breukink and De Kruijff 1999). Nisin is also more
effective in an acidic environment and some studies
have shown that there may be synergistic effects
depending upon the type of acid used with nisin
in solution.
Chitosan is derived from crustacean shells,
insect exoskeletons and cells walls of fungi. It
possesses antimicrobial activity due to its polycationic nature which allows it to react readily
with negatively charged molecules and surfaces
such as microbial cell walls. Chitosan is a deacetylated version of chitin and has an abundance of
highly reactive amine groups (Wang 1992; No et al.
2002). The more amino groups present, the more
deacetylated the chitosan. It is not possible to
produce fully deacetylated chitosan. Commercially
available chitosan is typically available in the range
70–95% deacetylation (DA).
Chlorine dioxide (ClO2) is a gas that is rapidly
gaining attention for use as an antimicrobial agent
in active packaging systems. Unlike the previous
methods, it does not rely on direct surface contact
981
to be effective. It has FDA approval and its use to
reduce or eliminate microbial loads in a wide variety
of food products such as fruits and vegetables is
becoming more intriguing (Rulis 2001).
The following is an overview of several studies
performed in our laboratories over the past 4 years.
The overall objective of the research has been to
develop antimicrobial films and test their effectiveness for food-packaging applications.
Materials and methods
Coating of nisin onto films
The first phase of the study was to develop the
coating that was to act as a carrier for the nisin.
Based on a review of the literature, a cellulose-based
solution was chosen. The packaging film coating
was prepared by blending methyl cellulose (0.875 g)
and hydroxypropyl methyl cellulose (0.375 g) with
ethanol (25 ml) and PEG 400 (0.75 ml). Total
biopolymer concentration in final solution was
70/30% MC/HPMC on a dry weight basis. When
nisin was added to the coating, it was first dissolved
in 0.02 N acetic acid (pH 2) and added to distilled
water for initial activation of nisin and then blended
with the coating solution.
Initially, the maximum level of nisin allowed
for use in cheese products was chosen as the highest
level to be tested in the coating solution. A minimum
concentration of effectiveness of nisin in solution
was determined by Grower et al. (2004a). Nisin
film-coating solutions were prepared containing a
maximum level of 10 000 IU ml1 (2.5 g) as a stock
solution and serial dilutions ranging from 10 000 to
8 IU ml1 were used.
Once an optimal coating solution was developed,
it was applied to the surface of a packaging
film (Franklin et al. 2004; Grower et al. 2004a, b).
Low-density polyethylene (LDPE) was used as the
base film since it is one of the most commonly
used packaging films. Film samples were taped to a
20 20 cm glass plate and nisin-based (50 ml) or
control solutions (no nisin) were cast onto the film
with a thin-layer chromatography (TLC) plate
coater (CAMAG, Muttenz, Switzerland) to obtain
a 500-mm coating thickness. The coated LDPE was
dried at ambient conditions (22 C, 28% relative
humidity). Before testing, nisin-treated film and
control samples were cut into 10 10 mm squares
and treated under ultraviolet light with a ZetaTM
7400 (Loctite Corp., Newington, CT, USA) for
5 min to sterilize any contaminates on the film
introduced during production.
The degree to which nisin could diffuse
from the coating into a solution was studied
by Grower et al. (2004b). LDPE film was coated
K. Cooksey
Results and discussion
Nisin films
The range of effectiveness of nisin against
L. monocytogenes is shown in Figure 1. The results
indicate that a nisin level of 156 IU ml1 was the
minimum inhibitory concentration necessary to
inhibit L. monocytogenes. Therefore, 156 IU ml1
became the lowest amount of nisin to be added to the
coating for further studies. In addition to the nisin
level, the effect of different organic acids were tested
(Figure 2) to determine if they enhanced
the inhibitory effect of nisin, but all four acids
produced similar antimicrobial activity against
the pathogen and no significant differences in zones
of inhibition ( p > 0.05) were observed (Grower et al.
2004a).
Grower et al. also examined the physical properties
of the film. For example, film coatings containing
increasing levels of nisin appeared cloudier than
those with lower levels of nisin or no nisin. Note that
the composition of commercially prepared nisin
35
30
25
20
15
10
9
19
39
78
156
313
625
0
1250
5
2500
The specific objective was to study the antimicrobial effects of chitosan solutions with different
per cent DA values (90, 85, 80%) and determine
whether viscosity had an effect on the antimicrobial
properties of chitosan solutions with three different
per cent DA values (Campbell 2003). A spot on
lawn assay was used to determine the effectiveness
of the chitosan with 90, 85 and 80% DA (high and
low viscosity of each) against L. monocytogenes.
Films were made using 1 and 2% solutions of each
type of chitosan and statistical comparisons
( p < 0.05) were made using a one-way analysis
of variance.
Research was carried out to observe the effect of
chlorine dioxide and modified atmosphere packaging
on the quality of fresh chicken breasts under
refrigerated storage for 15 days (Ellis 2003). Each
chicken breast was inoculated with 4 logs cfu ml1
culture of Salmonella typhimurium NAR (nalidixic
acid-resistant strain) and placed into a barrier
foam tray. Fast or slow release chlorine dioxide
sachets were placed next to the chicken in each
package. A control set of packages that did not
contain a chlorine dioxide sachet was also included
in the study. Packages were flushed with either
100% N2 or 75% N2/25% CO2 and stored at 3 C.
Microbial analysis and sensory (appearance and
aroma) analysis were performed every 3 days for
15 days.
5000
Chitosan films
Chlorine dioxide in modified atmosphere packaging
10000
with a solution containing a high or low viscosity
methylcellulose and hydroxypropyl methylcellulose.
Films contained 10 000, 7500, 5000, 2500 or
0 IU cm2 nisin (control). Film samples were
placed into peptone water and 10-ml samples were
removed and placed onto spiral plated lawns of
L. monocytogenes.
A modification of the spot on lawn assay called
a film on lawn assay was used to determine the
effectiveness of the nisin-containing LDPE coated
film for inhibition of L. monocytogenes on tryptic soy
agar (TSA) plate and modified oxford plates
(Franklin 2002). LDPE film was coated with a
cellulose-based solution containing no nisin or
10 000, 7500, 2500 or 156.3 IU ml1 nisin.
Modified oxford (MOX) and TSA plates were
spiral plated with L. monocytogenes populations
ranging from approximately 7–10 log CFU cm2.
Film samples (10 10 mm) were placed onto the
inoculated plates. The effectiveness of film
coatings was determined by measuring the zones
of inhibition.
The main objective of the next study was to
determine the effectiveness of packaging films
coated with a methyl cellulose/hydroxypropyl
methyl cellulose (MC/HPMC) based solution
containing 10 000, 7500, 2500 or 156.3 IU ml1
nisin for controlling L. monocytogenes on the surface
of vacuum-packaged hot dogs (Franklin et al. 2004).
Barrier film coated with MC/HPMC-based
solution containing nisin or no nisin (control)
was heat sealed to form individual pouches.
Hot dogs were placed in control and nisincontaining pouches and inoculated with a five-strain
L. monocytogenes cocktail (approximately 5 log CFU/
package), vacuum sealed and stored for intervals of
2 h, 7, 15, 21, 28 and 60 days at 4 C. After storage,
hot dogs and packages were rinsed with 0.1%
peptone water. Diluent was spiral plated on MOX
agar and TSA and incubated to obtain counts
reported as CFU/package.
Mean zones of inhibition (mm)
982
Nisin concentration (IU ml−1)
Figure 1. Inhibition of Listeria monocytogenes using different
concentrations of nisin (IU ml1). Zones of inhibition for nisin
concentrations 78, 39, 19 and 9 IU ml1 are zero.
983
Effectiveness of antimicrobial food packaging materials
consists of 2.5% nisin, 77.5% sodium chloride
(NaCl), 12% protein (in the form of milk solids),
6% carbohydrate and 2% moisture. Field-emission
scanning electron microscopy was unsuccessful
for determining whether nisin was homogenously
dispersed within the cellulose matrix. However, it
was successful in confirming that the cloudiness
Mean zones of inhibition (mm)
25
20
15
10
5
0
Ascorbic
Acetic
Lactic
HCl
Acids
Figure 2. Means and standard deviations of zones of inhibition
(mm) measured against Listeria monocytogenes to determine the
effect of nisin dissolved in different types of acids. No significant
differences ( p > 0.05) were observed among acids.
of the film was attributed to the salt and milk solids
contained within the nisin preparation and not
nisin itself.
To determine whether nisin was released from the
cellulose-based coating, coated LDPE film samples
containing differing levels of nisin were placed in
peptone solution. As shown in Table I, nisin diffused
from the coating solution from 1 min to 8 h, did
not diffuse after 24 h and 4 days but exhibited zones
of inhibition after 8 days once the coating was
completely dissolved. The viscosity of the cellulosebased carrier had no effect (Grower et al. 2004b).
These results indicated that nisin can be released
from the coating into solution, but the rate of
release is not controlled.
Franklin (2002) determined the degree to which
L. monocytogenes could be inhibited on solid
media. Film coatings containing no nisin and
156.3 IU ml1 nisin had no inhibitory effect on
L. monocytogenes grown on TSA or MOX at 37 C
for 48 h and 4 C for 17 days (Tables II and III).
Films coatings containing 2500, 7500, and
10 000 IU ml1 nisin were effective for inhibiting
L. monocytogenes on both agars at both storage
conditions. Zones of inhibition were greater for
Table I. Mean zones of inhibition (mm) measuring the rate of release of nisin in solution over time from film coatings
made from high (H) and low (L) viscosities of methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC)
containing various concentrations of nisin.
1 min
30 min
60 min
8h
24 h
4 days
8 days
Control L
2500 L
5000 L
7500 L
10 000 L
0
0
2.75b
6.75a
7.38a
0
0
2.25c
3.50a–c
7.00a
0
0
0
5.00a
6.33a
0
0
0
3.50b
6.50a
0
0
0
0
0
0
0
0
0
0
0
0
4.83b,c
7.33a,b
8.33a
Control H
2500 H
5000 H
7500 H
10 000 H
0
0
2.25b
5.00a,b
7.38a
0
0
2.50b,c
3.50a,b,c
6.75a,b
0
0
0
4.50a
5.50a
0
0
0
3.25b
5.75b
0
0
0
0
0
0
0
0
0
0
0
0
5.17b,c
7.58a
7.70a
a,b,c
Superscripts indicate significant differences ( p < 0.05) among film coating treatments during each period.
Treatments that did not produce zones of inhibition were not included in statistical analyses.
Table II. Mean zones of inhibition (mm) from LDPE coated with 10 000 IU ml1 nisin solution. No zones of inhibition were observed from
LDPE coated with solutions containing 156.3 IU ml1.
Zone of inhibition (mm)—10 000 IU ml1
Population
(log CFU cm2)
7
8
9
10
TSA
(37 C, 48 h)
TSA
(4 C, 17 days)
MOX
(37 C, 48 h)
MOX
(4 C, 17 days)
12.45A,x
12.26A,a,x
11.70A,a,x
11.22a,x
17.81B,y
18.48B,y
17.93B,y
17.15y
*
25.4b,z
25.32b,z
23.19b,z
**
**
**
**
A,B
Superscripts indicate significant differences ( p < 0.05) when comparing between the same agar type and different incubation
temperatures (37 C vs. 4 C). a,b Superscripts indicate significant differences ( p < 0.05) when comparing between the different agar types
(TSA vs. MOX) and the same incubation temperature. x,y,z Superscripts indicate significant differences ( p < 0.05) when comparing the
same agar types (TSA or MOX) and different populations (log 7–10 CFU cm2). * LM growth not sufficient to measure zones of inhibition.
** LM eliminated from nisin-containing film side of agar.
984
K. Cooksey
Table III. Mean zones of inhibition (mm) from LDPE coated with 7500 and 2500 IU ml1 nisin solution.
Zone of inhibition (mm)
Nisin concentration
(IU ml1)
Population
(log CFU cm2)
TSA
(37 C, 48 h)
TSA
(4 C, 17 days)
MOX
(37 C, 48 h)
MOX
(4 C, 17 days)
8
9
10
7
8
9
10
11.66 1.28A,a,x
11.46 1.51A,a,x
11.16 1.51A,a,x
11.24 1.51A,a,x
10.98 1.51A,a,x
10.69 1.51A,a,x
10.64 1.72A,a,x
30.75 2.28B,x
33.28 1.79B,x
34.28 1.79B,x
*
23.52 2.28B,y
25.72 1.79B,y
23.33 1.79B,y
26.53 1.34b
22.12 1.52b
22.67 1.52b
22.80 1.52b
21.92 1.52b
19.60 1.52b
19.91 1.52b
**
**
**
**
**
**
**
7500
2500
A,B
Superscripts indicate significant differences ( p < 0.05) when comparing between the same agar type and different incubation
temperatures (37 C vs. 4 C). a,b Superscripts indicate significant differences ( p < 0.05) when comparing between the same LM populations
and different agar types (TSA vs. MOX) at the same incubation temperature for both 7500 and 2500 IU ml1 films. x,y Superscripts
indicate significant differences ( p < 0.05) when comparing between the same agar type and population at different nisin concentrations
(2500 and 7500 IU ml1). * LM growth not sufficient to measure zones of inhibition. ** LM eliminated from nisin-containing film side
of agar.
Table IV. Listeria monocytogenes (five-strain cocktail) populations on the surface of hot dogs packaged in film coated with methyl cellulose/
hydroxypropyl methyl cellulose solutions containing 10 000, 7500 and 2500 IU ml1 nisin or no nisin (control) when enumerated on
tryptic soy agar (TSA).
Storage (days)
1
Nisin (IU ml )
0
156.3
2500
7500
10 000
0
7
15
21
28
60
5.29 þ 0.26a,x
4.84 þ 0.45a,x
n.d.b
n.d.b
n.d.b
5.51 þ 1.16a,x
4.9 þ 0.21b,x
n.d.c
n.d.c
n.d.c
6.13 þ 0.50a,x
4.90 þ 0.16b,x
n.d.c
n.d.c
n.d.c
6.33 þ 0.24a,y
5.37 þ 0.45b,y
n.d.c
n.d.c
n.d.c
8.01 þ 1.83a,y
7.50 þ 2.29b,y
n.d.c
n.d.c
n.d.c
9.11 þ 0.93a,y
9.52 þ 0.43a,y
n.d.b
n.d.b
n.d.b
n.d., Populations were below the detectable limit (<2.9 log CFU/package) throughout the study.
a–c
Significant differences ( p < 0.05) between nisin treatments (no nisin, 2500 and 7500 IU ml1) for each day of storage.
differences ( p < 0.05) between the storage day for each treatment.
x,y
Significant
Table V. Listeria monocytogenes (five-strain cocktail) populations on the surface of hot dogs packaged in film coated with methyl cellulose/
hydroxypropyl methyl cellulose solutions containing 10 000, 7500, 2500 IU ml1 nisin or no nisin (control) when enumerated on modified
oxford agar (MOX).
Storage (days)
1
Nisin (IU ml )
0
156.3
2500
7500
10 000
0
7
15
21
28
60
5.28 þ 0.25a,w
4.80 þ 0.50b,w
n.d.c
n.d.c
n.d.c
5.45 þ 1.21a,w
4.49 þ 0.33b,w
n.d.c
n.d.c
n.d.c
5.82 þ 0.64a,w
4.42 þ 0.13b,w
n.d.c
n.d.c
n.d.c
6.07 þ 0.37a,w
5.34 þ 0.64b,x
n.d.c
n.d.c
n.d.c
7.95 þ 1.84a,x
7.50 þ 2.50b,y
n.d.c
n.d.c
n.d.c
9.06 þ 0.90a,x
9.40 þ 0.43a,z
n.d.b
n.d.b
n.d.b
n.d., Populations were below the detectable limit (<2.9 log CFU/package) throughout the study.
a–c
Significant differences ( p < 0.05) between nisin treatments (no nisin, 2500 and 7500 IU ml1) for each day of storage.
differences ( p < 0.05) between storage day for each treatment.
film coatings containing 2500, 7500 and
10 000 IU ml1 nisin incubated for 17 days at 4 C
(MOX and TSA) compared with those incubated
for 48 h at 37 C (MOX and TSA).
Franklin et al. (2004) also studied the effectiveness
of nisin-coated barrier bags for inhibition of
L. monocytogenes in vacuum-packaged hot dogs.
L. monocytogenes counts on hot dogs packaged
with 156.3 IU ml1 nisin level films decreased
slightly (approximately 0.5 log reduction) through
w–z
Significant
day 15 of refrigerated storage, but it was statistically
the same ( p > 0.05) as hot dogs packaged in
films without nisin after 60 days of storage
(Tables IV and V). Packaging films coated with a
cellulose-based solution containing 10 000 and
7500 IU ml1 nisin significantly decreased ( p < 0.05)
L. monocytogenes populations on the surface of hot
dogs by more than 2 logs CFU/package throughout
the 60-day study. Similar results were observed for
hot dogs packaged with 2500 IU ml1 nisin level films;
Effectiveness of antimicrobial food packaging materials
985
As shown in Table VI, all six types of
chitosan solutions equally inhibited growth of
L. monocytogenes on TSA and MOX agar for both
1 and 2% solutions (Campbell 2003). Films were
also produced using the same chitosan solutions,
and although films with good tensile, elongation and
permeation properties were produced (data not
shown), it was difficult to test their antimicrobial
properties using the film on lawn assay due to excess
curling of the film. A solution to this problem is to
use the film overlay method.
Table VI. Inhibition of Listeria monocytogenes by 1 and 2%
chitosan solutions on TSA and MOX agar.1
Chlorine dioxide modified atmosphere packaging
however, L. monocytogenes populations were
observed to be approximately 4 log CFU/package
after 60 days of refrigerated storage from plate
counts on TSA and MOX (Franklin et al. 2004).
Chitosan solutions
Log CFU ml1
Deacetylation (%)
90
90
85
85
80
80
Viscosity
4
5
6
High
Low
High
Low
High
Low
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ
þ, Inhibition only at the film/medium interface within the 7–8 mm
diameter of the applied chitosan droplet.
1
Data represent results that were identical for both types of agar.
Total plate counts for chicken (Figure 3) increased
steadily after 6–9 days of storage regardless of
package atmosphere or ClO2 treatment. However,
those treated with ClO2 sachets had 1.0–1.5 log
cfu/chicken breast lower total plate counts compared
with those without ClO2 sachets. After 15 days,
samples treated with ClO2 (fast and slow release
sachets) had significantly lower S. typhimurium
NAR populations (approximately 1 log) compared
with chicken which did not contain ClO2 sachets
(Figure 4). The ClO2 adversely affected the colour
Figure 3. Total plate count of chicken breasts (log cfu/chicken breast) stored at 3 C. Day 0 means were 5.51 log cfu/chicken breast for all
treatments.
986
K. Cooksey
Figure 4. Salmonella typhimurium (NAR strain) counts (mean þ pooled standard error) of chicken breasts (log cfu/chicken breast) stored
at 3 C. Day 0 means were 3.95 log cfu/chicken breast for all treatments.
Table VII. Sensory panel aroma values (mean þ pooled standard error) of chicken breasts stored at 3 C.
3
6
9
15
ClO2
release
100% N2
75% N2/
25% CO2
100% N2
75% N2/
25% CO2
100% N2
75% N2/
25% CO2
100% N2
75% N2/
25% CO2
None
Fast
Slow
4.9 8.75a,y
6.0 8.75a,x
4.1 8.75a,z
6.2 8.75f,y
5.5 8.75f,x
5.6 8.75f,z
6.6 11.7a,x
4.6 11.7a,w
5.0 11.7a,y
5.5 11.7f,x
5.4 11.7f,w
7.4 11.7f,z
8.6 10.1b,y
3.4 10.1a,x
4.1 10.1a,z
6.0 10.1f,y
3.8 10.1f,x
6.6 10.1f,z
10.4 12.0b,y
5.0 12.0a,x
6.5 12.0a,z
9.8 12.0g,y
5.7 12.0f,x
7.5 12.0f,g,z
Day 0 means 0.52 for all treatments. 0 ¼ fresh (a fresh reference sample was provided); 15 ¼ off odour.
a,b
Significant differences within columns (100% N2 atmosphere) for each day of storage. f,g Significant differences within columns (75% N2/
25% CO2 atmosphere) for each day of storage. w,x,y Significant differences within rows (ClO2 release rates) for each day of storage.
of the chicken, as areas close to the sachet were
brown or green. No off odour (Table VII) was
detected by the sensory panellists (Ellis 2003).
Conclusions
Based on the above studies, nisin was found to be
an effective antimicrobial agent and the package
coating solution successfully served as a carrier
for the nisin. The effectiveness of the nisin was
reduced when incorporated into the coating
matrix as compared with a solution, but levels of
2500 and 7500 IU ml1 significantly reduced the
population of L. monocytogenes on hot dogs for
60 days of refrigerated storage. This also demonstrates the importance of testing an antimicrobial
packaging system using solutions, agar and food
systems for best overall results. Chitosan was also an
effective antimicrobial material, but there was no
advantage in using differing levels of the percent
DA or viscosities with regard to inhibition of
L. monocytogenes. Chlorine dioxide combined with
modified atmosphere packaging reduced the population of S. typhimurium NAR in fresh chicken,
but it was less effective against the natural microflora and had an adverse effect on the colour of
the chicken placed close to the sachets. All antimicrobial packaging systems showed promise for
reducing the population of selective bacteria in food
and each also had some conditions that require
further study to make them practical for industrial
applications.
Effectiveness of antimicrobial food packaging materials
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