PROCESSING AND PRODUCTS
Effect of Electron Beam Irradiation on Poultry Meat Safety and Quality1
S. J. Lewis, A. Velásquez, S. L. Cuppett, and S. R. McKee2
Department of Food Science and Technology, University of Nebraska-Lincoln,
Lincoln, Nebraska 68583-0919
ABSTRACT The purpose of this study was to determine
the effectiveness of electron beam irradiation at doses of
1.0 and 1.8 kGy on the elimination of bacteria from boneless, skinless chicken breasts without significantly altering product quality. Microbial testing was conducted in
triplicate using a whole carcass rinse method with each
nonirradiated control group and an irradiation treatment
group consisting of 10 samples. Results indicated that
mean counts for coliforms, generic Escherichia coli, and
psychrotrophs were 3.13, 3.26, and 1.92 log10 cfu/200 mL
rinsate, respectively, in the control samples. However,
these populations were not detected after the samples
were irradiated with 1.0 or 1.8 kGy. Mean count of 4.60
log10 cfu/200 mL rinsate was detected for aerobic bacteria
in the control samples. Irradiation doses of 1.0 and 1.8
kGy reduced the levels to 2.23 and 1.62 log10 cfu/200 mL
rinsate, respectively. Irradiation also rendered the fillets
free of Salmonella and Campylobacter. Consumer taste panels (product stored for 0, 14, and 28 d at 0 C) indicated
that, at Day 0, there were no differences among controls
and treatment groups for any of the quality attributes
tested. At Day 14, texture and flavor attributes were lower
for the irradiated groups. At Day 28, samples irradiated
with 1.0 and 1.8 kGy were less desirable with decreased
texture, flavor, and overall acceptability. Degree of lipid
oxidation also increased as storage time and level of irradiation increased. Irradiated samples also had higher a*
values, indicating they were pinker in color.
(Key words: irradiation, electron beam, poultry, quality of poultry meat, oxidation)
2002 Poultry Science 81:896–903
poultry (Federal Register, 1990). Later in 1992, the Food
Safety and Inspection Service approved irradiation doses
of 1.5 to 3.0 kGy for elimination of bacteria in raw packaged poultry (Federal Register, 1992). FDA approval of
irradiation of red meats, such as beef and lamb in 1997,
was part of a presidential initiative in which the goal
was to reduce the number of consumers suffering from
foodborne illnesses.
The two most commonly used sources of irradiation
are gamma rays (Cobalt60) and electron beams. During
the process of gamma irradiation, highly purified Cobalt60
produces gamma rays during its transformation down to
a stable state of nickel60 (Diehl, 1995; Satin, 1996). Gamma
rays can penetrate the entire product. In contrast to
gamma irradiation, electron beam irradiation uses accelerators that can generate electron beams of energy levels
up to 10 MeV, which are directed to the product with a
magnet (Nieto-Sandoval et al., 2000; Satin, 1996). Electron
beams can penetrate products with a thickness of 2 to
4 inches.
Even though electron beams are less penetrating than
the gamma rays, they are thought to offer several advantages over gamma irradiation (Satin, 1996). These advantages include higher dose rate capability, no nuclear
INTRODUCTION
Pathogenic microorganisms such as Campylobacter, Salmonella, and Escherichia coli 0157:H7 are naturally found
in the intestinal tracts of food-producing animals. Raw
meat and poultry products can become contaminated
with these pathogens during slaughtering and processing. It is estimated that 76 million foodborne illnesses
occur each year with 325,000 hospitalizations and 5,000
deaths and can reach an estimated annual cost of $23
billion (Mead et al., 1999). Of the 76 million foodborne
illnesses that occur each year, 2.5 to 2.9 million illnesses
are related to meat and poultry.
The use of irradiation to improve the safety of meat
and poultry products has received considerable attention
since the Food and Drug Administration (FDA) approved
the use of irradiation to control Trichinella spiralis in pork
in 1985 (Federal Register, 1985). In 1990, the FDA approved the use of irradiation to control salmonellae in
2002 Poultry Science Association, Inc.
Received for publication August 27, 2001.
Accepted for publication December 11, 2001.
1
This research was supported by Surebeam Corporation, San
Diego, CA.
2
To whom correspondence should be addressed: smckeehensarlingl
@unl.edu.
Abbreviation Key: FDA = Food and Drug Administration; MPN =
most probable number; TBARS = TBA-reactive substances.
896
ELECTRON BEAM IRRADIATION, POULTRY MEAT, AND SAFETY
waste, and the fact that the accelerators can be switched
on and off. A more important advantage is that the electron beam irradiation can be applied in a bi-directional
manner in which the irradiation can come into contact
with the food product from the top and bottom of the
sample. This penetration can offer the advantage of a
more uniform application of the irradiation, which can
lead to a more effective elimination of bacteria, particularly on product surfaces.
Because electron beams are less penetrating than the
gamma rays, they are also thought to have less of an
effect on the quality of the product. Hanis et al. (1989)
reported that gamma irradiation doses of 1.0 kGy resulted
in an increase in the level of oxidation in poultry meat.
As a result, the product received lower scores for flavor
and taste attributes when compared to nonirradiated
product during sensory evaluation. Lee et al. (2001) also
reported that electron beam irradiation results in an increase in the amount of cholesterol oxides that are formed
in poultry meat. However, the researchers did not conduct sensory evaluation to determine how cholesterol
oxides affect the overall quality of the product. Because
poultry products are thought to be pathogen free in the
center of an intact muscle, it is possible that only the
surface of the product needs to be irradiated, which may
result in less of an effect on the quality of the product.
Researchers have shown that both sources are effective
in reducing bacteria in food products such as poultry.
Patterson (1988) reported showed that bacteria in deboned chickens such as Salmonella typhimurium, E. coli,
and Moraxella phenylpyruvica were very sensitive to
gamma irradiation, especially when subjected to various
atmosphere changes. A study by Thayer et al. (1991) indicated that gamma irradiation was effective in reducing
S. typhimurium at doses as low as 0.90 kGy by 8.9 log
units. Thayer and Boyd (1991) also revealed that a gamma
irradiation dose of 1.8 kGy reduced the population levels
of S. typhimurium by 2.59 logs, and a dose of 2.7 reduced
the levels by 5.67 logs in mechanically deboned chicken
meat. Results from a study by Heath et al. (1990) indicated
that electron beam irradiation doses as low as 1.0 kGy
were effective in reducing Salmonella and aerobic bacteria
in broiler thighs and breasts.
The purpose of this research was to determine the effectiveness of electron beam irradiation of 1.0 and 1.8 kGy
on the elimination of bacteria in boneless, skinless chicken
breasts. The effects of irradiation on the quality attributes
of the breast fillets were also evaluated along with level
of oxidation produced by the irradiation.
MATERIALS AND METHODS
Irradiation of Test Samples
Packaged boneless, skinless chicken breasts were obtained from a commercial processing plant and trans3
Model DP-301, 101 Williams Drive, Ramsey, NJ.
Stomacher Lab-Blender, Model ‘400’ Closure Bags, Seward Medical,
London, UK.
5
3M Petrifilm, 3M Microbiology Products, St. Paul, MN.
4
897
ported to a commercial irradiation facility. Packaged samples were placed on ice (4 C) in styrofoam coolers and
transported to the irradiation facility, which was approximately 2 h from the processing plant. Broiler breast fillets
were packaged four fillets per polystyrene tray and were
shrink-wrapped with polyethylene overwrap.
The experiments were conducted in triplicate with each
treatment group consisting of 10 samples; four breasts in
a tray constituted one sample. At the irradiation facility,
the samples were randomly divided into two treatment
groups of 1.0 and 1.8 kGy and a control group receiving no
irradiation. A commercial scale electron beam accelerator
was used to apply the desired amount of irradiation to
the samples in a bi-directional manner in which the irradiation came into contact with the food product from the
top and bottom of the sample. The amount of radiation
received was measured by using Far West Technology
dosimeters that were placed in standard dosimeter plates
and passed through the irradiation system. The relative
energy of the system was 10 MeV coupled with 50 kW
of power, and irradiation was carried out at ambient
temperature. All samples were placed on ice (4 C) and
transported to the lab (3 h).
Color Determination
Sample colors were examined with a Minolta colorimeter.3 Breast fillets from each of the 10 sample trays were
analyzed by taking an average of measurements from
three locations on the top surface of the breast fillets. The
Hunter L*a*b* system was used in which L (±, lightness/
darkness), a (±, red/green), and b (±, yellow/blue) values
were measured at the three different areas on the fillets.
Higher L* values represented samples that were lighter
in color, and lower L* values indicated darker-colored
samples. Samples that were redder in color were represented by a positive a* value, whereas a negative a* value
indicated more of a green color.
Microbiological Evaluation
After the samples were transported from the irradiation
facility, they were held at 4 C to ensure that the samples
were at the same temperature for testing. After color determination was conducted on the breast fillets, the fillets
were tested for microbial levels. Each treatment group
consisted of 10 samples, with four breasts per tray constituting one sample. All experiments were done in triplicate. Each sample of four fillets was placed in sterile
stomacher bags4 and rinsed for 1 min with 200 mL of
buffered peptone water. Serial dilutions were made using
sterile buffered peptone water. E. coli and coliform populations were determined using E. coli petrifilm plates5 in
duplicate. Plates were incubated at 37 C for 24 h for
coliforms and 48 h for E. coli. To determine total aerobic
plate counts and psychrotroph counts, total aerobic petrifilm plates were used in duplicate. Plates were incubated at 37 C for 48 h for total aerobic plate microorganisms and 10 d at 4 C for detecting psychrotrophs.
898
LEWIS ET AL.
For detection of Salmonella, pre-enrichment was done
by placing 50 mL of the rinse in dilution bottles and
holding them overnight in an incubator at 37 C. An additional 35 mL of the rinse was stored at 0 C for enumeration. The next day, 0.1 mL of the rinse was inoculated in
Rappaport-Vassiliadis broth,6 and 0.5 mL was inoculated
in tetrathionate broth for selective enrichment and incubated for 24 h at 37 C. Samples were then streaked on
XLT4 agar base plates and incubated for 48 h at 37 C. Black
colonies on the XLT4 plates were considered Salmonella
positive and were confirmed with triple sugar iron agar
slants. Samples that were positive on the triple sugar iron
agar slants were serologically confirmed with Salmonella
O antiserum poly A-I and Vi test kits.7 Positive samples
were enumerated for Salmonella by the most probable
number (MPN) procedure, whereas negative samples
were discarded.
For Salmonella enumeration, the MPN procedure was
used in which the samples were dispensed into nine tubes
of buffered peptone water and incubated overnight at
37 C. Samples were then transferred to nine tubes of
tetrathionate broth and incubated overnight at 37 C. Each
tube was streaked on XLT4 plates and incubated for 48
h at 37 C. Black colonies were considered positive and
were confirmed with TSI slants and the serological kits.
Population levels were determined using the MPN table
from the Official Methods of Analysis (AOAC, 2000).
For Campylobacter detection and enumeration, 35 mL
of the rinse was centrifuged, and the pellet was resuspended in buffered peptone water. The samples were
transferred to filtercap flasks8 that contained 10 mL of
Bolton broth9 supplemented with Bolton broth selective
supplement along with buffered peptone water. Defibrinated horse blood was also added to the broth. The
containers were placed in anaerobic gas chambers10 with
atmosphere-generating systems (ascorbic acid) and were
incubated in anaerobic gas chambers at 42 C for 32 h.
After 32 h, the samples were streaked on modified CCDA
plates and incubated at 42 C for 32 h. Plates that contained
cream-colored colonies were considered Campylobacter
positive and were confirmed with a latex agglutination
kit11 specific for Campylobacter. Population levels were
determined using the MPN table from the Official Methods
of Analysis (AOAC, 2000).
Sensory Evaluation
Sensory evaluation was conducted with untrained panelists in the Department of Food Science and Technology
with 59, 53, and 52 panelists participating on Days 0, 14,
6
Difco Laboratories, Sparks, MD.
7
Difco Laboratories, Detroit, MI.
8
Nunc Filtercap Flasks, Nalge Nunc International, Naperville, IL.
9
Oxoid LTD, Basingstoke, Hampshire, UK.
10
Anaero Pack Rectangular Jars, Remel, Lenexa, KS.
11
Indx Campy (jcl) test kits, Intergrated Diagnostics, Inc., Baltimore, MD.
12
E-Z Pak Nylon/Poly Boil-In Pouches, Koch Supplies, Inc., Kansas
City, MO.
and 28, respectively. Samples from each treatment group
were randomly selected, repackaged in cook-in bags12
and stored for 0, 14, and 28 d at 0 C in non-oxygen
permeable packaging. On each day of sensory testing, the
fillets were baked on covered aluminum trays in a gas
fired Reel oven set at 177 C to an internal temperature
of 76 C. The samples were held in a warm oven at 93 C
(<1 h) until they were served to the panelists. The cooked
fillets were cut into 2- × 4-cm cubes and placed in plastic
containers that were preassigned random three-digit
numbers. The panelists were served one sample at a time
and asked to rate each sample using a modified nine-point
hedonic scale. The hedonic scale included the attributes of
appearance (like to dislike), texture (moist to dry), flavor
(like to dislike), and overall acceptability (like to dislike).
On Day 0 only, each panelist was asked to make a visual
evaluation of the chicken breast fillets and state which
sample had the most desirable color.
Analyses of TBA-Reactive Substances
The degree of oxidative deterioration of the lipids in
the fillets was measured by the TBA-reactive substance
(TBARS) analysis method of Witte et al. (1970). TBA values represented the secondary product of lipid oxidation
and were expressed as milligrams of malondialdehyde
per kilogram. During the repackaging of the samples for
storage, samples from each treatment group were randomly selected for TBARS analysis. Samples were stored
for 0, 14, and 28 d in a freezer at 0 C, and TBARS analysis
was conducted on duplicate samples at each storage period. Before analysis, fillets were baked on covered aluminum trays in a gas-fired Reel oven set at 177 C to an
internal temperature of 76 C. Samples were cooked to
represent oxidation associated with storage and subsequent cooking. After being cooled for 30 min, the fillets
were ground and mixed with 1 mL of butylated hydroxytoluene (BHT) solution. Forty-four milliliters of the extracting solution (10% trichloroacetic acid in 0.1 M phosphoric acid) was added, and the sample was homogenized until it was solubilized. The homogenate was
filtered through a Whatman #1 filter, and 5 mL of filtrate
was transferred to a test tube. Five milliliters of the TBA
reagent was added to the test tube, and then the solution
was vortexed. After being placed in a boiling water bath
for 30 min, the sample was cooled and absorbance was
read at 532 nm. Sample TBA values were obtained by
comparing the sample absorbance at 532 nm to a standard
curve of 1,1,3,3-tetraethoxypropane (TEP) in extracting
solution.
Statistical Analyses
The treatments were assigned in a completely randomized manner, and the experiment was repeated three
times. Colony-forming units were multiplied by 200 (200
mL rinse solution used) to estimate the total bacterial load
recovered from the breast fillets and were transformed to
log10 cfu/200 mL rinsate (McKee et al., 1998). The 0 cfu
ELECTRON BEAM IRRADIATION, POULTRY MEAT, AND SAFETY
TABLE 1. Population levels in chicken breast fillets before and
after irradiation; means and standard errors
Population (log10 cfu/200 mL rinsate)
Bacteria
Control
1
Coliforms
Escherichia coli1
Psychrotrophs
Total plate counts
a
3.13
3.26a
1.92a
4.60a
±
±
±
±
0.06
0.05
0.21
0.07
1.0 kGy
<1.15
<1.15b
<1.15b
2.23b
b
±
±
±
±
0.00
0.00
0.00
0.08
1.8 kGy
<1.15b
<1.15b
<1.15b
1.62c
±
±
±
±
0.00
0.00
0.00
0.09
a-c
Mean values with the same superscript within the same row are
not significantly different (P < 0.05).
1
Coliform counts were recorded after petrifilm plates were incubated
for 24 h, and E. coli counts were recorded from the same petrifilm plates
after 48 h of incubation.
should be <2.3 (log10 cfu/200 mL rinsate) based on this
calculation. Because 0 cannot be directly analyzed with
the statistical model, we used a value equivalent to half
of 2.3 log10 cfu/200 mL rinsate (1.15 log10 cfu/200 mL
rinsate). Data were analyzed with the general linear
model of SAS software, and a probability level of P <
0.05 indicated significance (SAS Institute, 1999). Duncan’s
multiple range tests were used to test for differences
among the means. Sensory evaluation was conducted using a randomized complete block design with panelists
serving as the replicates. Data from the cooked samples
were analyzed on each day by one-way ANOVA to test
for treatment effects. At the completion of the study, the
total data set was subjected to a two-way ANOVA to test
for time and time × treatment effects. The data from the
raw samples were analyzed by one-way ANOVA to test
for treatment effects.
RESULTS AND DISCUSSION
The effectiveness of irradiation against pathogens is
mainly due to hydrogen peroxide production that results
from the generation of free radicals during irradiation.
Hydrogen peroxide acts as a potent antimicrobial and
can eventually result in the production of long-lived hypochlorite, which is very toxic to pathogens (Kuby, 1997).
As a result, mutations that result in loss of normal functions of the bacteria and reduce their pathogenic potential
can occur (Satin, 1996; Hayes et al., 1995; Farkas, 1989).
The results of this study indicate that irradiation doses
of 1.0 and 1.8 kGy were effective in eliminating bacteria
in the boneless, chicken breasts fillets.
Electron beam irradiation treatment at 1.0 and 1.8 kGy
reduced coliforms, E. coli, aerobic bacteria and psychrotrophs when compared to controls receiving no irradiation treatment (Table 1). However, no differences were
detected in any of these microbial populations between
the 1.0 and 1.8 kGy treatment groups (Table 1). Although
coliforms, E. coli, and psychrotrophs were eliminated using 1.0 and 1.8 kGy of irradiation, aerobic bacteria populations were greatly reduced but not completely eliminated.
Heath et al. (1990) also found that an electron beam irradiation dose as low as 1.0 kGy results in a 2 to 3 log cycle
reduction in the total number of aerobic organisms but
899
does not totally eliminate the organisms in broiler breast
and thigh pieces. In a study by Nieto-Sandoval et al.
(2000), it was shown that an electron beam irradiation
dose of 2.4 kGy is effective in reducing Enterobacteriaceae
counts as well as coliforms and total mesophilic bacteria
in spices. Nieto-Sandoval et al. (2000) indicated that there
were 2 to 3 log reductions in the microbiological counts.
The present study showed that the numbers for the
controls were relatively low when compared to other
studies, such as Heath et al. (1990). The relatively low
numbers were due to the fact that boneless, skinless breast
fillets, such as those used in the study, are expected to
have low microbial loads because the fillets do not have
skin for the bacteria to attach to. It is thought that chicken
parts such as thighs that have skin will have higher microbial loads because the bacteria are mostly attached to
the skin. In the study by Heath and co-workers, higher
microbial loads were likely found because they were using thighs and breast pieces with attached skin. Also, the
researchers tested for aerobic organisms only, whereas
in the present study, we also tested for the presence of
coliforms, generic E. coli, and psychrotrophs. As a result,
there was no basis for comparison for the latter organisms.
Several other studies have also been conducted to determine the effectiveness of irradiation against other bacteria, such as spoilage organisms, that are normally found
in poultry products. Hanis et al. (1989) showed that Pseudomonas aeruginosa was eliminated from broiler carcasses
at irradiation with 1.0 to 2.5 kGy, whereas Serratia marcescens was eliminated by doses of 2.5 to 5.0 kGy. In a study
by Thayer and Boyd (1992), irradiation doses as low as
0.26 and 0.36 kGy resulted in a reduction in Staphylococcus
aureus population in mechanically deboned chicken meat.
Thayer and Boyd (1992) also indicated that no viable
colony-forming units were found in samples irradiated
at 1.5 kGy.
The effect of irradiation with 1.0 or 1.8 kGy on Salmonella and Campylobacter populations was also determined
in the current study. The MPN procedure was used to
enumerate the Salmonella and Campylobacter populations,
but because the numbers were so low, the percentage of
positive samples that was found will be reported. Results
show that 40% of the samples in the control groups were
positive for Salmonella (Figure 1). However, none of the
samples were positive for Salmonella in the 1.0 and 1.8
kGy irradiation groups, indicating that the irradiation
eliminated Salmonella. Because Salmonella was eliminated
at 1.0 and 1.8 kGy, no differences were found between
the irradiation treatment groups.
Results also show that 13% of the samples were positive
for Campylobacter, but none of the irradiated samples were
positive (Figure 1). Similar to the results of Salmonella,
irradiation doses of 1.0 and 1.8 kGy eliminated Campylobacter from the samples. However, no differences were
found between the 1.0 and 1.8 kGy treatment groups.
Heath et al. (1990) also found that an electron beam irradiation dose of 1.0 kGy could totally eliminate Salmonella
in broiler breasts and thigh pieces. Patterson (1995)
showed that an irradiation dose of 1.0 kGy resulted in
900
LEWIS ET AL.
FIGURE 1. Percentage of positive samples for Salmonella and Campylobacter in the irradiated and nonirradiated samples. a,b;x,yMean values with
the same superscript are not significantly different (P < 0.05).
an approximate 5-log reduction in the population level
of Campylobacter jejuni in sterile poultry mince. However,
the effectiveness of irradiation varied among other
Campylobacter strains.
Results of our study show that even though electron
beams are thought to be less penetrating than gamma
rays, the electron beams were just as effective in eliminating the bacteria from the breast fillets as the gamma
rays used in previous studies.
We also determined the effect of irradiation at 1.0 and
1.8 kGy on the overall color of the product. Results for
color determination show that irradiation doses of 1.0
and 1.8 kGy had no effect on the L* values when compared to the non-irradiated controls (Table 2). High L*
values indicate samples light (white) in color, whereas
low L* values indicate samples dark in color. Although
no differences in L* values were found among the treatment groups and controls, differences in a* and b* values
were detected. Specifically, a* values were higher in
irradiated samples, indicating they were pinker in color.
Moreover, the a* value for the irradiation dose of 1.8
kGy was higher than the irradiation dose of 1.0 kGy,
suggesting that increasing levels of irradiation deepen
TABLE 2. Minolta’s color values of the irradiated and
nonirradiated breast fillets; means and standard errors
Treatment
Control
1.0 kGy
1.8 kGy
L* value
a* value
b* value
52.57a ± 0.34
52.34a ± 0.26
52.30a ± 0.31
3.75a ± 0.08
4.85b ± 0.11
5.31c ± 0.13
3.64a ± 0.30
3.37ab ± 0.31
2.74b ± 0.32
a-c
Mean values within the same column with the same superscript
are not significantly different (P < 0.05).
meat color. Results of the study also show that the b*
values were higher for the control group than for the
1.8 kGy indicating meat with more of a yellow color.
However, the 1.0 and 1.8 kGy groups were not different
from one another nor were the control and 1.0 kGy
groups. Visual evaluation of the raw chicken breasts
indicated that as the level of irradiation increased, there
was an increase in desirability (Table 3). Based on panelists’ comments, the 1.8 kGy samples were visually perceived to have a pinker and fresher appearance, whereas
the controls were perceived as having a grayer color.
Results similar to those found in our study have also
been observed in other studies. A study by Byun et al.
(1999) indicated that irradiation with 3 and 5 kGy caused
significant increases in a* values in raw and cooked pork
loins. The higher a* values indicated that the irradiation
caused the pork loins to have a redder color. It is thought
that in cured meats, irradiation causes activated oxygen
to react with iron-porphyrin prosthetic heme group and
results in a bright pink color because of the formation
of nitrosyl ferro-hemochromogen. Bernofsky et al. (1959)
also reported that during irradiation, oxymyoglobin is
first converted to metmyoglobin, which is in turn converted to a red compound. This conversion can result
in the product having a redder color and, thus, a higher
a* value.
Irradiation not only impacts microbial quality and
safety, but it may also influence other quality attributes
of meat products such as flavor and texture due to the
increase in lipid oxidation. In this study, sensory evaluation results indicate that at Day 0, no differences were
found among treatments for appearance, texture, flavor,
and overall acceptability (Table 3). On Day 14, although
901
ELECTRON BEAM IRRADIATION, POULTRY MEAT, AND SAFETY
TABLE 3. Sensory evaluation of baked chicken breast fillets treated with increasing levels of irradiation
and stored at 0 C for up to 28 d; means and standard errors
Time (d)
0
14
28
Treatment
Control
1.0 kGy
1.8 kGy
Control
1.0 kGy
1.8 kGy
Control
1.0 kGy
1.8 kGy
Appearance1
6.41a
6.33a
6.30a
6.36x
6.23x
6.44x
6.74A
6.27B
6.75A
±
±
±
±
±
±
±
±
±
0.13
0.13
0.13
0.14
0.14
0.14
0.14
0.14
0.14
Texture2
6.56a
6.03a
6.44a
6.79x
6.47x
5.92y
6.89A
6.16B
6.40B
±
±
±
±
±
±
±
±
±
Flavor1
6.46a
6.27a
6.25a
6.38x
6.06x
5.83y
6.83A
6.20B
6.13B
0.18
0.18
0.18
0.19
0.19
0.19
0.19
0.19
0.19
±
±
±
±
±
±
±
±
±
0.18
0.18
0.18
0.17
0.17
0.17
0.19
0.19
0.19
Overall
acceptability3
6.52a
6.44a
6.30a
6.53x
6.17x
6.07x
6.78A
6.15B
6.04B
±
±
±
±
±
±
±
±
±
0.16
0.16
0.16
0.16
0.16
0.16
0.18
0.18
0.18
Color
desirability
1.24a
2.22b
2.56c
.
.
.
.
.
.
± 0.15
± 0.15
± 0.15
..
..
..
..
..
..
a-c;x-z;A,B
Mean values within the same column with the same superscript are not significantly different (P <
0.05). . . . Data were not collected.
1
Where 9 = like extremely; 5 = neither like nor dislike; 0 = dislike extremely.
2
Where 9 = extremely moist; 5 = neither moist nor dry; 0 = extremely dry.
3
Where 3 = most desirable; 1 = least desirable.
no differences were found among control group and
irradiation treatment groups for the appearance and
overall acceptability, there was a difference in texture
and flavor attributes among the nonirradiated groups
and irradiation treatment groups. No difference in texture and flavor was found between the 1.0 and 1.8 kGy
treatments. Results showed that dryness increased as
the irradiation level increased, and flavor decreased as
the irradiation level increased (Table 3). On Day 28,
texture, flavor, and overall acceptability attributes were
higher for the control samples, and there was no difference in the quality attributes between the 1.0 kGy and
1.8 kGy irradiated samples. For the appearance attribute,
there was no difference between the control and the 1.8
kGy treatment group; however, the 1.0 kGy treatment
had a lower appearance score compared to the other
groups.
Hashim et al. (1995) found similar results in a study
conducted to determine consumer acceptance of irradiated poultry products. In the study, participants bought
irradiated breasts and thighs and cooked them in their
home. Participants were asked to rank the cooked samples based on color, appearance, flavor, mouthfeel, and
overall acceptability using a nine-point hedonic scale.
Seventy-three percent of the participants gave the products a minimum rating of 7 (1 = dislike extremely, 5 =
neither like nor dislike, and 9 = like extremely), which
is similar to the results obtained in our study. Hashim
et al. (1995) also show that more consumers would be
willing to purchase irradiated products if provided more
information about these types of products. After the
educational program, the number of participants that
would buy irradiated boneless, skinless breasts increased significantly from 59.5 to 61.9%. Eighty-four percent also thought it necessary to irradiate raw chicken.
Other researchers have also found a positive correlation
between education and an increased willingness of consumers to purchase irradiated products (Hashim et al.,
1996; Resurreccion, 1995).
Results of the current study show that the electron
beam irradiation had a similar effect on final quality of
the product when compared with results by Hashim et
al. (1995). However, the previous researchers did not
look at the effect of irradiation on the quality of the
chicken breasts during storage. Also, the consumers
were not given nonirradiated control samples so there
was no basis for comparison. Even though the quality
of our product decreased as the storage period increased, our product received similar attribute rankings
after 28 d of storage as the product in the previous study
with no storage period. Reduction in quality depicted
by the panelists may be attributed to the increased level
of lipid oxidation caused by irradiation, which results
in a less desirable product. Results indicate that gamma
irradiation might have been more detrimental to the
quality of the product when compared to electron
beam irradiation.
Because irradiation is thought to increase lipid oxidation due to free radical generation, TBARS analysis was
conducted to test for any relative increase in lipid oxidation. When the samples were tested for their levels of
TBARS (reported as mg/kg malondialdehyde), treatment and time effects were found (Table 4). Within each
test time, as the level of electron beam irradiation in-
TABLE 4. 2-Thiobarbituric acid-reactive substances (TBARS) of
chicken breast fillets treated with increasing levels of irradiation
and stored at 0 C for up to 28 d; means and standard errors
Time (d)
0
14
28
Treatment
Control
1.0 kGy
1.8 kGy
Control
1.0 kGy
1.8 kGy
Control
1.0 kGy
1.8 kGy
TBARS
(mg/kg malondialdehyde)
0.12a,A
1.25b,A
1.67c,A
0.45a,B
2.04b,B
4.14c,B
0.79a,C
2.32b,C
4.26c,B
±
±
±
±
±
±
±
±
±
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
a-c
Means with different superscripts in a column within a time are
significantly different (P < 0.05).
A-C
Means with different superscripts in a column between times are
significantly different (P < 0.05).
902
LEWIS ET AL.
creased, there was an increase in the TBA values indicating increased oxidation. In addition, as storage time
increased, the TBA values within each treatment increased (Table 4). This result is to be expected because
irradiation causes electrons to enter an electrically
charged state and they can then function as free radicals.
This free radical state results in lipid oxidation, and a
higher level of irradiation would produce a higher level
of oxidation (Satin, 1996).
Byun et al. (1999) also showed that as irradiation increased from 3 to 5 kGy, the TBA values for the irradiated and cooked pork loin hams also increased significantly. An increase in TBA values was also found as the
storage time increased up to 30 d. A second study by
Hanis et al. (1989) showed that the peroxide value, which
is also an indicator of oxidation, of irradiated poultry
meat did increase after irradiation. However, the increase was dependent on the mean temperature during
irradiation. At −15 C, the peroxide value increased from
5.6 to 10.1 when an irradiation dose of 1.0 kGy was
applied. The peroxide value increased to 29.4 when 10.0
kGy was used. Results were similar but slightly higher
for 10 C. As stated earlier, irradiation causes electrons
to become free radicals, which results in lipid oxidation.
Higher doses of irradiation cause more free radicals to
be formed and higher oxidation, leading to higher TBA
and peroxide values.
Not only is lipid oxidation due to free radical formation a concern, but also the formation of cholesterol
oxides during irradiation (Lee et al., 2001). During cholesterol oxidation, oxidative products such as 7-hydroxycholesterol and 7-ketocholesterol are formed, which
have been reported to produce cytotoxic, angiotoxic,
and carcinogenic effects (Nawar, 1996). Lee et al. (2001)
reported that cholesterol oxides are formed during irradiation, but the oxides formed at different rates depending on the type of packaging. Cholesterol oxides
were formed at a faster rate in irradiated, cooked chicken
meat that had been stored in aerobic packaging. When
vacuum packaging was used, irradiation had no consistent effects on the amount of cholesterol oxides that were
produced in cooked chicken meat. However, during
storage, the amount of 7 α-hydroxycholesterol and 7ketocholesterol significantly increased in the irradiated,
cooked chicken meat that was vacuum-packaged.
The current study reveals that electron beam irradiation resulted in an increase in lipid oxidation just as
gamma irradiation, but the level of cholesterol oxides
produced were not studied. In the previous study of
Byun et al. (1999), the peroxide value (indicator of oxidation) analysis was conducted with raw samples; however, the samples in our study were cooked before lipid
oxidation analysis. Cooking might have increased the
final level of oxidation. Despite this increase, level of
oxidation produced by the electron beam irradiation at
1.0 kGy was actually lower when compared to the same
gamma irradiation of 1.0 kGy used in other studies
(Byun et al., 1999). Therefore, electron beam irradiation
may be less detrimental to meat quality.
Based on the results of this study, electron beam irradiation is an effective means of eliminating bacteria from
breast fillets even at the minimum dose of 1.0 kGy. An
irradiation dose of 1.0 kGy was also effective in improving the color of the breast fillets. Sensory evaluation
revealed that electron beam irradiation resulted in a
decrease in the texture, flavor, and overall acceptability
of the product as the storage period increased. The observed decrease in product quality can be attributed to
increased level of oxidation due to irradiation.
ACKNOWLEDGMENTS
We are grateful for the support of this study by Surebeam Corporation, San Diego, CA.
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