Figure 1: HP apparatus Figure 2: Sample basket

1
Salmonella destruction in frankfurters using
hydrostatic pressure and bacteriocins
A.W. Wolf, S. Bandyopadhyaay, N. Kalchayanand, B.
Ray, and W.J. Means Meat Science and Food
Technology Group, Department of Animal Science,
University of Wyoming, 82071-3684 USA
INTRODUCTION

• Salmonella causes an estimated 3 million cases of
  foodborne illness annually
• As a non-thermal process,hydrostatic pressure
  (HP) is attractive to industry as an alternative
  processing method
• We hypothesized that HP would have a synergistic
  effect when combined with bacteriocins of lactic
  acid bacteria against gram-negative microorganisms

Figure 6 Typical Industrial HP system
Figure 5 Cut-away Diagram of HP system
OBJECTIVE Determine the effectiveness of HP in
conjunction with bacteriocins at destroying
Salmonella in inoculated frankfurter packs
RESULTS and DISCUSSION

• Log reduction (viability loss) of Salmonella
  strains
• Pure Culture (Table 1)
• 0.2 log cfu/mL to greater than 5.5 log cfu/mL
  following HP25
• 1.3 log cfu/ml to greater than 6.8 log cfu/mL
  following HP50
• 5-strain cocktail (Table 2)
• 1.2 log cfu/mL (HP25)
• 5.3 log cfu/mL (HP25Bmix)
• 5.3 log cfu/mL (HP50)
• 6.8 log cfu/mL (HP50Bmix)
• As Figure 7 indicates, viability loss of a log
  cfu/mL concentration of cocktail-inoculated
  frankfurter packs was 0.2 log /mL with Bmix, 5.4
  log cfu/mL with HP50 treatment, and 6.7 log
  cfu/mL with combined HHP50 and Bmix treatment.

MATERIALS and METHODS

• Ten strains of Salmonella were obtained from the
  USDA laboratory and the University of Wyoming
  Food Microbiology culture library
• S. anatum MH24209, S. anatum MH24594, S.
  enteritidis FDA , S. enteritidis WSVL, S.
  muenster MH24461, S. typhimurium ATC014028, S.
  Typhimurium E 21274, S. Typhimurium MH21423, S.
  Typhimurium MH24231 and S. 6,7k monophasic, C1
  MB3710
• Hydrostatic pressurization unit (Engineered
  Pressure Systems, Andover, MA)
• Capable of pressurizing to 690 MPa at 25 to 95C
• Pressure increased at a rate of 138 MPa min-1 and
  returned, after dwell time, to atmospheric
  pressure within 2 min

Table 1 Viability loss (log cfu/ml) of ten
strains of Salmonella following treatment with
345MPa at 25C for 5 min (HP25) or 345MPa at 50C
for 5min (HP50)

• Figure 1 HP apparatus Figure 2 Sample
  basket
• Treatment groups
• Non-inoculated control (C-)
• Inoculated control (C)
• 2500au Nisin 2500au Pediocin (Bmix)
• 345 MPa for 5 min at 25?C (HP25)
• 345 MPa for 5 min at 50?C (HP50)
• bacteriocin mixture (Bmix) was made consisting of
  2500 au nisin 2500 au pediocin.
• 10 strains of Salmonella were subjected to 345
  MPa for 5 min at 25 or 50 C
• Grown to early stationary phase in TSY broth
• 3 ml placed in cryovials
• HP25
• HP50
• Enumerated on TSY
• 5-Strain cocktail, chosen for their relative HP
  resistance and/or prevalence in food-borne
  illness outbreaks
• S. anatum MH24209, S. enteritidis FDA, S.
  muenster MH24461, S. Typhimurium MH21423, and S.
  Typhimurium MH24231
• 11111 ratio
• 3 ml placed in cryovials

Table 2 Viability loss (log cfu/ml) of an
equal-ratio 5-strain cocktail of Salmonella by
hydrostatic pressure (HP, 345 MPa for 5 min) at
25C or 50C for 5min (HP50) and with 2500au
Nisin 2500au Pediocin (BHP)
Strains used were S. anatum MH24209, S.
enteritidis FDA, S. muenster MH24461, S.
Typhimurium MH21423, and S. Typhimurium MH24231
Results indicate that HP50, especially in
conjunction with Bmix is a viable method of
ensuring Salmonella destruction in processed
meats. Similar results have been reported using
similar treatments in other studies (Larsen,
2000, Yuste et al., 2000 Ray et al., 2001b). Of
particular interest is the synergistic effect
observed with HP50 and bacteriocins, which are
typically of limited effectiveness against
gram-negative species of bacteria, including
Salmonella. We postulate that this may be due to
morphological changes to the lipopolysaccharide
layer of the cellular membrane. Hydrostatic
pressure has been documented to cause changes to
this membrane, which may allow bacteriocin access
to the inner membrane (site of activity).
IMPLICATIONS Hydrostatic pressure (345 MPa for 5
min at 50?C), in conjunction with bacteriocins of
lactic acid bacteria, would be effective in
eliminating Salmonella found as a post-lethality
contamination in frankfurters
References Larsen, G.A. 2000. Efficiency of
high hydrostatic pressure and bacteriocins on
death of pathogens on processed meat products.
M.S. Thesis, Univ. Wyoming Ray, B., N.
Kalchayanand, P. Dunne, and A. Sikes. 2001b.
Microbial destruction during hydrostatic pressure
processing of food. pp 95-122 In Bozoglu, F. T.
Deak, and B.Ray (eds.) Novel processing control
technologies in the food industry. IOS Press,
Amsterdam, Netherlands. Yuste, J., R. Pla, and M.
Mor-Mor. 2000. Salmonella enteritidis and
aerobic mesophiles in inoculated poultry sausages
manufactured with high pressure processing.
Letters in Applied Microbiology. 31 374-377.
Figure 3 Frankfurter sample packs
Figure 4 Plates following enumeration