Arkansas - Agricultural Communication Services - University of ...

AAES Research Series 488
Antimicrobial treatment application and sample processing.
Treatment combinations for this study included: 1)
5% (vol:vol) acetic acid solution (Shurfine Inc., Northlake,
IL) followed by 0.5% (wt:vol) cetylpyridinium chloride solution
(Zeeland Inc., Zeeland, MI)(AC); 2) 200 ppm (vol:vol)
chlorine dioxide solution (Midland Chemical Company,
Lenexa, KS) followed by 0.5% (wt:vol) cetylpyridinium
chloride solution (CC), 3) 0.5% (wt:vol) cetylpyridinium
chloride solution followed by 10% (wt:vol) trisodium phosphate
solution (Rhone Poulenc, Cranbury, NJ)(CT) and 4) an
untreated control (C). All antimicrobial treatments were prepared
in deionized water with the exception of acetic acid,
which was commercially prepared.
For antimicrobial application, beef trimmings were
placed into a Lyco meat tumbler (Model 4Q, Lyco Inc.,
Janesville, WI) with 400 ml of the first antimicrobial treatment
(either 5% acetic acid, 200 ppm chlorine dioxide or
0.5% cetylpyridinium chloride), aerobically tumbled for 3
minutes (16 rpm), then removed from the tumbler and placed
into a clean tumbler with 400 ml of the second antimicrobial
treatment (either 0.5% cetylpyridinium chloride or 10%
trisodium phosphate), and tumbled again for another 3 minutes
(16 rpm) aerobically.
Upon completion of the antimicrobial application
phase, beef trimmings were removed from the tumbler and
ground twice using a Hobart grinder (Model 310, Hobart Inc.,
Troy, OH) with a 3.2 mm plate. The ground beef was divided
into 1 lb samples and packaged on styrofoam trays with
absorbent diapers. The trays were overwrapped with
polyvinyl chloride film with an oxygen transmission rate of
1400 cc/m 2 /24 hr/1 atm (Borden Inc., Dallas, TX) and stored
under simulated retail display conditions (39.2°F; deluxe
warm white fluorescent lighting, 1630 lx, Phillips Inc.,
Somerset, NJ). Fat content was standardized to 10% and validated
using a Hobart Fat Analyzer (Model F101, Hobart Inc.
Troy, OH). Ground beef pH was determined immediately
after grinding for each treatment and was 5.72 for C, 4.71 for
AC, 5.70 for CC and 6.91 for CT. For this, 1.8 g of ground
beef was homogenized in 18 ml of distilled water and evaluated
using an Orion Model 420A pH meter with a ROSS electrode
(Model 8165BN, Orion Research, Inc., Beverly, MA).
Microbial sampling. On days 0, 1, 2, 3, and 7 of simulated
retail display, 25 g of ground beef was aseptically
removed from the packages and placed into whirlpack bags
(Nasco, Ft. Atkinson, WI) with 225 ml of 0.1% buffered peptone
water and buffered to a pH of 7 with either sodium
hydroxide or hydrochloric acid. Samples were then stomached
in a Model 400 Lab Stomacher (Seward, London,
United Kingdom) for 2 minutes and serial dilutions were
made. Subsequent duplicate platings were made on
Salmonella shigella agar (Difco Laboratories, Detroit, MI)
containing nalidixic acid, Petrifilm ® (3M Corp., St. Paul,
MN) aerobic plate count (APC) plates and Petrifilm ® E.
coli/coliform plate count plates. Plates were then incubated at
98.6°F in an aerobic incubation chamber (either VWR Model
5015 or Model 3015 incubators, VWR Scientific, West
Chester, PA) and APC along with Salmonella shigella agar
plates were read at 48 hours, while E. coli/coliform plates
were read at 24 hours. Counts were recorded as colony forming
units per gram (CFU/g).
Statistical analysis. The experiment was replicated
three times. The randomized complete block factorial experiment
was analyzed using the GLM procedure of SAS (SAS
Inst., Inc., Cary, NC). Treatments were blocked by replicate
then analyzed for the main effects of antimicrobial treatment
combination, day of display and appropriate interactions. For
variables involved in interactions, interaction means were
generated, separated using the PDIFF option of GLM, and
plotted. Least-squares means for all other variables were generated
and separated using the PDIFF option of GLM.
Results and Discussion
Effect of antimicrobial treatment combinations on
microbial populations. The effect of multiple antimicrobial
intervention treatments on the reduction of Salmonella
typhimurium and aerobic plate count are shown in Table 1.
Salmonella typhimurium in ground beef was reduced (P <
0.05) 1.98, 1.38 and 1.17 log colony forming units (CFU)/g
by the acetic acid followed by cetylpyridinium chloride treatment
(AC), the chlorine dioxide followed by cetylpyridinium
chloride treatment (CC), and the cetylpyridinium chloride
followed by trisodium phosphate treatment (CT), respectively.
Aerobic plate counts (APC) of ground beef were reduced
(P < 0.05) by 1.76, 1.17 and 0.88 log CFU/g by AC, CC and
CT treatments, respectively. Various researchers have reported
that multiple antimicrobial interventions are more effective
than single interventions for reducing microorganisms on
carcasses or intact tissue (Gorman et al., 1995; Phebus et al.
1997). Graves-Delmore et al. (1998) concluded that the use
of sequential antimicrobial applications was more effective
for reducing microbial contamination on beef adipose tissue
than were individual decontamination treatments. They also
reported decontamination treatments were more effective in
reducing bacterial numbers when the initial contamination
level was high. Therefore, results from this study are in agreement
with Graves-Delmore et al. (1998) as well as Fratamico
et al. (1996), both of which used similar compounds to obtain
comparable microbial reductions on beef carcasses and tissues.
Likewise, reductions in microorganisms in this study
were also consistent with those of Gorman et al. (1995) and
Kochevar et al. (1997) on beef and lamb adipose tissue and
with those of Hardin et al. (1995) on beef carcass surfaces.
Effect of duration of display on microbial populations.
Salmonella typhimurium populations declined (P < 0.05) 1.21
log CFU/g through 7 days of display (Table 2). In addition,
APC was held in check (P > 0.05) through the duration of display.
Therefore, multiple antimicrobial intervention treatments
had a long-term lethal effect on ST while retarding aerobic
bacterial growth through refrigerated display.
Effects of antimicrobial treatment combinations and
duration of display on microbial populations. The day of display
by antimicrobial treatment interaction effect on E. coli
and coliform counts are shown in Figure 1 (panels A and B).
E. coli was reduced (P < 0.05) by all antimicrobial treatment
169