Microbial decontamination of beef carcasses by combination of steaming and lactic acid spray

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Journal of Food Engineering xxx (2004) xxx–xxx
www.elsevier.com/locate/jfoodeng
Microbial decontamination of beef carcasses by combination
of steaming and lactic acid spray
P. Pipek a,*, M. Hous?ka b, J. Jelen?´kova´ a, K. Ky´hos b, K. Hoke b, M. S?ikulova´ a
a Institute of Chemical Technology Praha, Technicka´ 3, 166 28 Praha 6, Czech Republic
b Department of Food Engineering, Food Research Institute Prague, Radiova´ 7, 102 31 Praha 10, Czech Republic
Received 8 January 2004; accepted 23 April 2004
Abstract
Under industrial conditions, the e?cacy of surface decontamination of beef carcasses was evaluated. The combination of steam
treatment followed by spraying with 2% solution of lactic acid was applied on the surface on the end of the slaughter line (30 min
p.m.). The total count of psychrophilic and mesophilic microorganisms were evaluated immediately after treatment and during cold
storage up to 5 days. The treatment was e?ective––reducing the surface micro?ora by one to three decimal orders of CFU during the
time of cold storage.
Ó 2004 Published by Elsevier Ltd.
Keywords: Microbial decontamination; Steam; Lactic acid; Beef carcass
1. Introduction
(2001). Steam has been shown to be e?ective in reduc-
ing the number of microorganisms on meat surfaces
Microbial contamination of meat starts during
(Morgan, Radewonuk, & Scullen, 1996; James et al.,
processing on the slaughter line. First, the microorgan-
1998). Gill and Bryant (1997) found that vacuum–hot
isms reach the carcass surface from where they penetrate
water cleaning (water and steam temperature >82 °C),
into deeper layers of the meat. Reducing this primal
pasteurizing treatments (105 °C for 6.5 s) and subse-
surface contamination and avoiding or limiting the
quent spray-cooling of cattle carcasses can be operated
microbial growth, we can considerably prolong the
in commercial practice to reduce log mean numbers of
shelf life of carcasses. Reducing surface contamination
coliforms and Escherichia coli by >2 and log mean num-
would improve food safety and extend shelf life (James,
bers of total aerobic bacteria by >1.
Thornton, Ketteringham, & James, 2000).
Decontamination treatments applied during dressing
Di?erent methods of heat treatment of surface layers
of cattle carcasses were investigated for their e?ects on
were suggested and evaluated. They involved hot water,
microbiological quality. Steam or hot pasteurization
steam and hot air and were tested on di?erent carcasses.
was shown to be consistently e?ective methods of reduc-
Immersion in hot water is one of many potential meth-
ing bacterial counts. Washing, followed by an e?ective
ods for reducing levels of pathogenic bacteria on the sur-
pasteurization treatment, provides the maximal possible
face of poultry meat Goksoy, James, Corry, and James
reduction in bacterial counts (Gill & Landers, 2003). In
opposite Bacon, Sofos, Belk, and Smith(2002) evalu-
ated the e?cacy of a commercial steam vacuum unit
*
(1.72 bar steam, 130 °C) in reducing Salmonella popula-
Corresponding author. Tel.: +420-2-24353198; fax: +420-2-
tions of inoculated, chilled cattle carcass adipose tissue.
33337337.
E-mail address: [email protected] (P. Pipek).
It was not achieved a su?cient reduction (>1 log/cfu/
0260-8774/$ - see front matter Ó 2004 Published by Elsevier Ltd.
doi:10.1016/j.jfoodeng.2004.04.033

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P. Pipek et al. / Journal of Food Engineering xxx (2004) xxx–xxx
cm2) may be due to too rapid movement of the steam-
heat decontamination of the surface. Such a treatment
application unit across the surface.
is limited by the possible heat damaging of the appear-
James et al. (2000) compared potential methods for
ance of carcass surface. At the same time the water tem-
decontaminating lamb carcasses applied at 50 min
perature must be above 75 °C (Siragusa, 1995).
post-mortem for 8 s: steaming at 100 °C, immersion in
The combination of physical treatment by hot steam
90 °C water and immersion in 90 °C chlorinated water.
withspraying by lactic acid solution is another possi-
Aerobic plate counts (55 min p.m.) were signi?cantly re-
bility for surface decontamination; see e.g. papers of
duced by all these; the steam system shows the best
Dorsa, Cutter, Siragusa, and Koohmaraie (1996) or
potential for industrial application due to its simplicity.
Dorsa, Cutter, and Siragusa (1996). In this case, acid
The advantage of steam is explained by Kozempel,
and heat inactivation of microorganisms follows release
Goldberg, and Craig (2003). The surface will appear
of microorganisms from the surface. The e?ect of
quite roughwithmany pores. It is di?cult to kill bacte-
combined treatment was recently proven by Kang,
ria that get into these pores with sanitizing solutions be-
Koohmaraie, Dorsa, and Siragusa (2001). They ob-
cause surface tension prevents the liquid from entering
served that di?erent combinations of hot water (82 °C)
the pores. Therefore, steam should be able to enter the
and/or hot air (510 °C) and lactic acid resulted in contin-
pores and kill the bacteria. A very thin layer of air plus
uously decreasing microbial populations on the beef
the entrained moisture surrounds all solid food and
trim.
steam cannot pass through these barriers to reach the
The reduction of di?erent indicator organisms on hot
bacteria. Apply vacuum to the food to remove the air
cattle carcass surfaces obtained by steam vacuuming
and moisture; rapidly apply steam to kill the bacteria
was signi?cantly smaller than those obtained by a com-
in the pores; then expose the food to vacuum again to
bination of steam vacuuming withsubsequent sanitizing
remove the condensate and evaporatively cool the sur-
treatments of hot water (95 °C at the nozzle), or warm
face. The times of exposure must be short, on the order
(55 °C) 2% lactic acid spray, Castillo, Lucia, Goodson,
of 0.1 s. A VSV process was developed (originally in-
Savell, and Acu? (1999). Similar process was proven
tended for chicken), that exposes meat to vacuum, then
as very e?ective also in our previous experiments under
steam, then vacuum again; using this the reduction of
laboratory conditions (Hoke et al., 2000).
di?erent pathogen by log 1.0–2.0 was achieved.
However, decontamination systems may adversely af-
Hoke, Hous?ka, Ky´hos, Landfeld, and Pipek (2003)
fect qualities that control carcass acceptability, i.e.,
published paper dealing with the surface heat transfer co-
ÔbloomÕ, colour and odour. An e?cient decontamination
e?cient as a function of time during vacuum–steaming–
system should reduce bacterial numbers without any
vacuum cooling of beef meat placed in the cook/chill vac-
detrimental changes to the appearance of the carcass
uum equipment. The paper also contains the procedure
(James et al., 2000). Goksoy et al. (2001) reported that
how to predict the real value of meat surface temperature
no immersion heat treatment (<90 °C) is capable of re-
by numerical modelling (application of Food Product
ducing contamination with E. coli, or similar thermotol-
Modeller software, MIRINZ New Zealand).
erant microorganisms, on raw poultry without causing
Use of organic acids reduces bacterial counts in the
adverse changes in the product.
meat surface layer; lactic acid is often used, as it is a nat-
From these reasons, the possible e?ect of the decontam-
ural meat compound produced during the post-mortem
ination treatment on the surface colour must be consid-
glycolysis. Moreover, the lactate anion slows down the
ered. The treatment with lactic acid had only a negligible
growthof surviving microbes during storage (Kotula
e?ect on the colour, see e.g. Pipek, Izumimoto, Hous?ka,
& Thelappurath, 1994; Siragusa, 1995). The application
Maly´, and Jelen?´kova´ (2001) or Pipek et al. (2004), but
of lactic acid is generally known and was e?ective also in
some problems may arise from the hot steam e?ect.
industrial conditions in previous trials, e.g. Staruch,
The goal for this study was to check the e?cacy of the
Chalupka, Sirotna´, and Heriban (2001), Pipek, Kadan?o-
combination of hot steaming and spraying with lactic
va´, Bac?o, and Br?ezina (1997) or Pipek, Izumioto, and
acid solution under industrial conditions over the whole
Jelen?´kova´ (2004).
period of 5 days of storage.
The fact, that the temperature of lactic acid solution
increases the e?ect of acid decontamination, was pro-
ven also in our previous experiments (Pipek, F?´la,
2. Materials and methods
Jelen?´kova´, Brychta, & Miyahara, in press). The combi-
nation of mechanical avoiding or releasing of bacteria
Di?erent methods of meat surface decontamination,
stuck on the carcass surface followed by antimicrobial
hot water, hot air, steaming and lactic acid spray were
spraying or spraying withhot water induces two steps
tested under laboratory condition (Hoke et al., 2000
(i.e. release and inactivation) necessary for the deconta-
and Pipek et al., 2000). As the combination of steaming
mination system to be e?ective (Siragusa, 1995). The
and lactic acid proven to be most e?ective this method
treatment by hot water combines the rinse and partial
was tested under industrial conditions.

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3
The e?ect of decontamination was studied in two
Table 1
phases. First, the reduction of microbial counts caused
Schema of the experiments
by steam and lactic acid was measured, in the next phase
Experiment
Contamination
Parts
the storage experiment was carried out and the micro-
A
Natural
Brisket at 7thrib
bial growth was evaluated over the whole 5 day period
B
Standardised
Brisket at 7thrib––muscle part
of cool storage starting at the moment of decontamina-
C
Increased
Brisket at 7thrib––adipose part
tion up to the moment of dissection. The main attention
D
Increased
Flank––muscle part
was given to the psychrophilic microorganisms, the
growthof wh
ichis anticipated during cold storage.
The mesophiles counts were also evaluated because of
the natural contamination was used, in one parallel
possible occasional interruption of the cold chain.
experiment these natural counts were arti?cially in-
creased by a solution prepared from the swabs on the
2.1. Materials
slaughterhouse.
In all experiments, ?ve beef carcasses were treated by
The experiments were carried out under industrial
steam and decontamination solution and ?ve beef car-
conditions in the large Czech meat plants. The beef car-
casses were used as control. Bothtreated and control
casses were treated immediately after dressing at the end
carcasses were stored in parallel (Table 1).
of slaughter line before entry in the chilling tunnel, i.e.
nearly 30 min post-mortem. After decontamination pro-
2.1.4. Experiment A
cedures, the carcasses were chilled in an air tunnel and
The microbial population on the surface of beef car-
stored under chilling temperature about +3 °C.
casses was not adjusted before the decontamination
The decontamination treatment involved the action
treatment; only naturally contaminated carcasses were
of the hot steam followed by the spraying with lactic
taken into consideration. The samples were taken from
acid.
the brisket at the seventh rib. In this experiment, only
the psychrophilic bacteria have been evaluated.
2.1.1. Steam
Highpressure steam at 6 bar was used. The steam
2.1.5. Experiment B
treatment was carried out witha special rectangular
Because of relatively high variability of initial micro-
nozzle having the width of 100 mm and height of 1 mm.
bial counts in experiment A, the surface was in this
experiment standardised using a wet plastic foam roller.
2.1.2. Time of steam action
Again, only natural contamination was used. The sam-
The steam ?ash emerging from the nozzle expanded
ples were taken from the brisket at the seventh rib. In
at the nozzle throat to atmospheric pressure and reaches
addition to the psychrophilic bacteria, the mesophiles
the temperature 100 °C at this point. Because we were
have been also taken into account.
able to keep the distance of the nozzle throat from the
carcass surface at about 20 mm, the stream temperature
2.1.6. Experiment C
at this point can be estimated at 90–95 °C and the
The initial microbial counts on the carcass surface
stream height at about 3 mm. The temperature of the
were increased before the experiment. The microorgan-
stream was veri?ed experimentally. The stream treat-
isms were applied in form of a solution prepared of
ment of the selected surface area was achieved within
swaps extremely contaminated carcasses; the roller from
one second. The length of the treated area was about
plastic foam was used for application of this solution.
240 mm. The mean time of the steam action on the indi-
Five beef carcasses were treated by steam and by
vidual site can be calculated from stream height, length
lactic acid decontamination solution. The samples were
of the treated area and stream height and equals to 1 * 3/
taken from the adipose parts on the brisket surface
240=0.013 s.
between the third and ?fth rib. Both the psychrophilic
microbes and the mesophiles have been taken into
2.1.3. Lactic acid solution
account.
The solution for the decontamination was prepared
by dilution of 2% of L-(+)-lactic acid (Purac FCC 80,
2.1.7. Experiment D
PURAC biochem, Gorinchem Netherlands) in water.
This experiment was carried out in other meat plant
The temperature of solution in the moment of treatment
withsome small modi?cation. The steam pressure was
was equal to 45 °C. A manual sprayer was used for
in this case 4 bars. The carcasses were sprayed with lac-
application of the solution to the carcass surface.
tic acid solution by an automatic device on the end of
The samples for microbiological evaluation were ta-
the slaughter line instead of by a manual sprayer.
ken from those parts of carcasses where high surfaces
The initial microbial counts on the carcasses surface
contamination was anticipated. During the experiment,
were increased before experiment. The microorganisms

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were applied in form of solution prepared of swaps ex-
reduction. The total decrease of microbial counts after
tremely contaminated carcasses; the roller from plastic
decontamination treatment can be estimated as one dec-
foam was used for application of this solution.
imal order. The average of the counts decreased from
The samples for microbiological evaluation were ta-
4 · 102 to 2 · 101 gÀ1. However, it is evident, that the
ken from surface muscle tissue on the ?ank close to
microbial counts were very low and very variable so that
the hide limb.
the e?ect of decontamination treatment was little appar-
Control samples were taken from the ?rst ?ve car-
ent. The microbial growth took place during the cold
casses, when the automatic spraying device was o?. Both
storage, see Fig. 1. Very variable values made di?cult
the psychrophilic and the mesophilic microorganisms
the evaluation of the experiment. Nevertheless, it is evi-
have been taken into account.
dent that the shelf-life of carcasses is prolonged and the
e?ect of decontamination is apparent even at the end of
2.2. Methods
the 5 days storage.
In the experiment B, the decontamination of steam
The samples for the microbiological analysis were ta-
and lactic acid on the surface of beef carcasses was
ken from the same carcass before decontamination, after
investigated after foregoing standardisation using a
steam treatment, after spraying withlactic acid and then
plastic foam roller. This operation facilitated the evalu-
after 24, 96 and 120 hof cold storage. Control samples
ation of the e?ect of the decontamination treatment, as
were taken from the other half of the same carcass.
the scatter of values was lower.
The sampling is reported in the literature made by
The treatment by the steam caused a decrease of the
swabbing or excision. James et al. (2000) undertook
surface contamination and the following spraying with
sampling using the wet and dry swabbing method for
lactic acid solution duplicated this reduction. The total
lamb carcasses. As the excision is reported to be the
decrease of microbial counts after decontamination
more e?ective sampling method to recover and sub-
treatment can be estimated as one decimal order (see
sequently enumerate bacteria than sponge swabbing
Figs. 2 and 3). During the cold storage, the microbial
(Bacon et al., 2002) we preferred the method of abscis-
sion of surface layer. We also expected the in?ltration
of microorganisms in the deeper layers during subse-
100000
decontaminated
quent storage experiment.
]-1 10000
control
The surface layer of meat––nearly 5 mm thick was
thus used for microbiological evaluation. The samples
1000
of dimension of 40 · 40 · 5 mm were aseptically cut from
the carcass surface, placed in plastic bags and under
100
chilling conditions immediately transferred to microbio-
10
counts of psychropilic [g
logical laboratory.
The total counts of mesophilic microorganisms were
1
0
20
40
60
80
100
120
140
determined according to the C
? SN ISO 4833 standard.
time [h]
Each10 g of sample were homogenised with100 g of
physiological solution and diluted following the ex-
Fig. 1. The growth of psychrophiles during storage of decontaminated
pected microbial counts. One milliliter of diluted sample
beef carcasses in experiment A (every point represents average of ?ve
samples).
was placed on Petri discs and covered by 15 ml of PCA
(plate count agar, temperature of 40–45 °C). After mix-
ing, the Petri discs were stored at a temperature of 37 °C.
After 24 or 48 hof cultivation, the total counts were re-
10000
treated
lated to 1 g of the sample.
]
control
-1
The total counts of psychrophilic microorganisms were
1000
determined on the same way, only cultivation was car-
ried out on PCA agar 72 hat 15 °C (C
? SN ISO 560100
100
standard).
10
counts of mesophiles [g
3. Results and discussion
1
0
20
40
60
80
100
120
In the experiment A only psychrophilic microbes have
time [h]
been evaluated. The treatment with steam caused a weak
Fig. 2. The growth of mesophiles during storage of decontaminated
reduction of microbial counts on the surface; the follow-
beef carcasses in experiment B (every point represents average of ?ve
ing spraying withlactic acid solution duplicated th
is
samples).

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P. Pipek et al. / Journal of Food Engineering xxx (2004) xxx–xxx
5
10000
100000
treated
treated
]
]
control
-1
-1
control
1000
10000
100
1000
counts of psychropilic [g
counts of mesophiles [g
10
100
0
20
40
60
80
100
120
0
20
40
60
80
100
120
time [h]
time [h]
Fig. 3. The growth of psychrophiles during storage of decontaminated
Fig. 4. The growth of mesophiles during storage of decontaminated
beef carcasses in experiment B (every point represents average of ?ve
beef carcasses in experiment C (every point represents average of ?ve
samples).
samples).
counts changed insigni?cantly, the counts at treated
samples were lower than control ones.
However, it is evident, that the counts of microorgan-
10000000
]
treated
isms on the surface are very low and so the e?ect of
-1 1000000
control
decontamination was not apparent enough. In this
100000
experiment, at the end of storage (after 80 h) the counts
of psychrophiles were slightly lower at untreated sam-
10000
ples then at treated ones. From this reason, in next
1000
experiment C we increased arti?cially the initial contam-
counts of psychropilic [g
100
ination.
The di?erence between mesophilic and psychrophilic
10
0
20
40
60
80
100
120
microorganisms is not de?nite. Generally, the counts
time [h]
of mesophiles were lower as these of psychrophiles; the
e?ect of decontamination was similar at bothmicrobial
Fig. 5. The growth of psychrophiles during storage of decontaminated
beef carcasses in experiment C (every point represents average of ?ve
groups.
samples).
Because of low contamination (due to good hygiene
in the meat plant), during the next experiment we have
chosen another place on the carcass (adipose part of
After 4 days of storage the growth of psychrophiles in
the brisket). In addition to this, we increased the surface
bothsamples (decontaminated and control) was much
microbial counts by arti?cial contamination by a solu-
more pronounced then the growth of mesophiles that
tion prepared from swaps of extremely contaminated
even decreased on the ?fth day.
carcasses; the plastic foam roller was used for applica-
The retard of microbial growth on treated samples
tion of this solution.
can be ascribed to the e?ect of lactate ions from the
In the experiment C, the choice of the other place and
decontamination solution on the surface layer. The
the increase in initial microbial counts before experiment
di?erences in the psychrophilic counts on the surface
proved to be suitable. Decontamination by steam and
between treated and control samples at the end of the
lactic acid on the surface of beef carcasses (adipose part
storage were nearly three decimal orders.
of the brisket) caused an immediate reduction in micro-
Experiment D was carried out in the other meat
bial counts and of bothpsychrophilic, as well as me-
plants. The initial microbial counts on the carcasses sur-
sophilic microorganisms. The steam treatment induced
face were higher as in experiments A–C. This was due to
a decrease of one decimal order, and the following
poor hygiene in the factory and testing on another part
spraying by lactic acid caused a decrease more than
of the carcasses (?ank). In addition, in this case we also
one decimal order; the total decontamination e?ect in
increased the initial microbial counts before the experi-
this case is thus more then two decimal orders (see Figs.
ment.
4 and 5).
The decontamination e?ect of steam and lactic acid
These results correspond to results published by
on the surface of beef carcasses was proven also in this
Castillo et al. (1999) con?rming the synergic e?ect of
experiment (see Figs. 6 and 7). The treatment by steam
steaming washand lactic acid spray.
and lactic acid induced a decrease in microbial counts.
During the forced air chilling and cold storage the
During the following storage, the growth of both psy-
microbial counts increased. There were evident di?er-
chrophilic and mesophilic microorganisms occurred,
ences between mesophilic and psychrophilic counts.
that of psychrophiles being more rapid. At the end of

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P. Pipek et al. / Journal of Food Engineering xxx (2004) xxx–xxx
1000000
shelf life and improvement in food safety. This process
can be also utilised as a manual treatment of parts of
]
100000
-1
carcasses visually evaluated as impure.
10000
4. Conclusions
1000
treated
Decontamination of beef carcasses by steam and lac-
control
counts of mesophiles [g
tic acid immediately reduced the surface microbial
100
0
10
20
30
40
50
60
70
counts and retarded microbial growthduring storage.
time [h]
The e?ect is higher on more contaminated parts of the
carcasses. Suchtreatment can be used to prolong shelf
Fig. 6. The growth of mesophiles during storage of decontaminated
life and to increase food safety of beef carcasses.
beef carcasses in experiment D (every point represents average of ?ve
samples).
Acknowledgment
1000000
treated
]-1
control
This work was supported by Ministry of Agriculture
100000
of the Czech Republic, grant number QE0186.
10000
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1000
counts of psychropilic [g
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Document Outline
  • Microbial decontamination of beef carcasses by combination of steaming and lactic acid spray
    • Introduction
    • Materials and methods
      • Materials
        • Steam
        • Time of steam action
        • Lactic acid solution
        • Experiment A
        • Experiment B
        • Experiment C
        • Experiment D
      • Methods
    • Results and discussion
    • Conclusions
    • Acknowledgment
    • References