Control of Listeria
monocytogenesKelly J.K. Getty, Ph.D.
Kansas State University
Control and Growth of Listeria monocytogenes
Packaging effects on jerky, snack sticks, kippered beef steak, and turkey tenders
Intrinsic factors in sliced deli turkey roast
Effect of salts
Package Systems and Storage Times Serve as Post-Lethality Controls for Listeria
monocytogenes on Whole Muscle Beef Jerky and Pork and Beef Smoked Sausage
Sticks
J. Food Prot. (2011) 74:188-192
Support provided by the USDA CSREES under agreement 2003-34211-12998, the Kansas Department of Commerce and Housing, Agriculture Marketing Division, and Oberto Sausage Company
BackgroundA “zero” tolerance policy is applied by USDA to Lm in ready-to-eat meat and poultry products
USDA defines a post lethality treatment as a process that reduces Lm by at least 1 log
Research has shown packaging can generate a 1 log Lm reduction following 1 or more weeks of storage at ambient temperature
Objective To determine the effect of
packaging environment and storage time on reducing Listeria monocytogenes on whole muscle beef jerky and pork and beef smoked sausage sticks
MATERIALS AND METHODS
Experimental DesignJerky cut into square pieces
Dipped into Lm inoculum
Dry Jerky ~ 1 h
Measure Water Activity
Four packaging treatments
applied
Hold for 24, 48, 72 h and 30
days
Plates incubated for 24 hours at
35˚C
Enumeration of initial level
of Lm
Enumeration after storage
periodsPlates incubated for 24 hours at
35˚C
Inoculum Procedures Five strains of Lm were used to prepare a
cocktail inoculum. One loopful of each strain placed into 9 mL
test tubes of tryptic soy broth (TSB). Incubated for 24 hours at 35˚C.
From the test tubes, 0.5 mL was pipetted into 200 mL jars of TSB. Incubated for 24 hours at 35˚C
Contents of jars were combined to create 1 L 5 strain cocktail
Sampling Procedures Jerky was aseptically cut into 4 x 4 cm2
pieces.
Dipped for 1 minute in 5 strain cocktail of Lm.
Allowed to air dry for 1 hour.
Packaged using four treatments: - Nitrogen Flush with - Vacuum (VAC) oxygen scavenger (NFOS)- Heat Seal with - Heat seal (HS) oxygen scavenger (HSOS)
Samples held for 0, 24, 48, 72 h and 30 days
Enumeration of Listeria monocytogenes
4 x 4 cm2 was placed in a stomacher bag and 34 mL of peptone water was added.
Samples were stomached for 1 minute.
Serial dilutions were prepared. 0.1 mL of each dilution was
spread plated onto modified Oxford medium (MOX) plates.
Plates were incubated at 35˚C for 24 hours.
RESULTS
24 h 48 h 72 h 30 d0
0.5
1
1.5
2
2.5
3
3.5
4
HSHSOSNFOSVAC
Storage Time
Mea
n L
og R
euct
ion
(lo
g C
FU
/cm
2)
ab
abc
a
bc
f
f
a
bc
cd
c
bc
bc
de
e
ff
f f
de
Mean Log Reduction of Lm on Beef Jerky Packaged in Different Packaging Environments and Stored at Ambient Temperature
abcde Means having a different superscript differ (P<0.05)
HS HSOS NFOS VAC0
0.5
1
1.5
2
2.5
3
3.5
Packaging Treatment
Mea
n l
og r
edu
ctio
n (
CF
U/c
m2)
a
b
b
b
Mean Lm Log Reduction (CFU/cm2) on Smoked Sausage Sticks Packaged in Different Packaging Environments
24 h 48 h 72 h 30 d0
0.5
1
1.5
2
2.5
3
3.5
Time of Storage
Mea
n l
og r
edu
ctio
n (
CF
U/c
m2)
a
ab
b
c
Mean Lm Log Reduction (CFU/cm2) on Smoked Sausage Sticks During Ambient Temperature Storage
Conclusions Jerky - Using these packaging
environments in conjunction with at least a 48 h storage time is a Lm post lethality control treatment.
Snack Sticks - Using these packaging environments in conjunction with at least a 24 h storage time is a Lm post lethality control treatment.
Effect of Packaging and Storage Time on
Survival of Listeria monocytogenes on
Kippered Beef Steak and Turkey Tenders
J. Food Sci. (accepted)
Objective Determine the effect of packaging
environment and short term storage time on reducing Listeria monocytogenes in meat or poultry snacks
Materials and Methods Two commercially obtained products:
Kippered Beef Steak: Lean beef components, ground and
formed Cured Product
Turkey Tenders: Whole muscle turkey breast, sliced
and marinated Uncured Product
Experimental Design 4 packaging treatments X 4 storage times X 2
samples/treatment X 3 replications
Packaging treatments: Heat sealed (HS) Heat seal with oxygen scavenger
(HSOS) Nitrogen flushed with oxygen
scavenger (NFOS) Vacuum (VAC)
Storage times: 0, 24, 48, or 72 h
ProceduresProduct cut into squares or
used as intact strips
Dip into Lm inoculum for 1 min
Dry Product ~1 h at ambient
temperatureMeasure awPackage in 1 of 4
treatments
Hold for 24, 48, or 72 h at ambient temperatureIncubate plates for
48 h at 35˚C
Spread plate for initial Lm level
(time 0 h)
Spread plate following storage time
Product Characteristics
Kippered Beef Steak Turkey Tenders
SOI MPR ≤ 2.03:1 MPR ≤ 2.03:1
Moisture (%) 38.3 32.1
Protein (%) 29.2 35.9
Fat (%) 6.1 2.5
Salt (%) 5.4 4.0
MPR 1.31 0.89
aw 0.83 0.81
pH 6.0 5.6
Kippered Beef Steak Turkey Tenders
Time (h) Mean aw Time (h) Mean aw
Prior to Dip 0.81 Prior to Dip 0.77
0 0.80 0 0.81
24 0.80 24 0.81
48 0.82 48 0.82
72 0.81 72 0.81
Mean aw During Ambient Time Storage
Heat sealed Heat sealed with oxygen scav-
enger
Nitrogen flushed with oxygen scavenger
Vacuum packaged
0
1
2
3
24 h
48 h
72 h
Mea
n L
og
Red
uct
ion
(C
FU
/cm
2)p
er D
ayMean log reductions (CFU/cm2) of Listeria monocytogenes in kippered beef steak
Heat sealed Heat sealed with oxygen scavenger
Nitrogen flushed with oxygen scavenger
Vacuum packaged 0
1
2
3
24 h
48 h
72 h
Me
an
Lo
g R
ed
uc
tio
n (
CF
U/c
m2
) p
er
Da
yMean log reductions (CFU/cm2) of Listeria monocytogenes in turkey tenders
Implications
Processors of these products could use a combination of vacuum or nitrogen flushing and a hold time of 24 h prior to shipping to reduce potential Lm by at least 1 log.
However, processors should be encouraged to hold product for at least 72 h to enhance the margin of safety.
Effect of Intrinsic Factors on Growth of
Listeria monocytogenes in Sliced Deli Turkey
Roast
We acknowledge Cargill Meat Solutions for support of this project.
Objectives Evaluate how sodium nitrite
concentration, percent pump, and salt type affect the growth of L. monocytogenes in vacuum packaged sliced turkey deli roast stored at 4°C for up to 91 days.
Materials and Methods
Sliced turkey deli roasts were formulated with 1.5% sodium chloride (NaCl) or 0.75% NaCl and 0.75% potassium chloride, 10% or 45% pump, and 0 ppm or 200 ppm sodium nitrite (NaNO2) for a total of eight treatments.
Turkey slices were inoculated with a 5-strain Lm cocktail (inoculated) or peptone water (control) and then vacuum packaged.
Materials and Methods
After 0, 7, 14, 21, 28, 42, 63, and 91 days of 4C storage, treatments were sampled for Lm populations on modified oxford media (MOX) and aerobic plate count (APC).
pH, water activity (aw), residual nitrite, and percent fat, moisture, protein, and sodium was measured using control treatments for each sampling day.
Results Lm populations in turkey deli roast slices
containing 200 ppm NaNO2 were 0.70 to 2.39 log CFU/cm2 lower (P<0.05) compared with products formulated with 0 ppm NaNO2.
Using 10% pump reduced (P<0.05) Lm populations by 0.62 to 1.50 log CFU/cm2 on days 7 to 28 and at day 63 compared with products pumped to 45%.
Results Incorporating 1.5% NaCl or 0.75% NaCl and
0.75% KCl into turkey formulations did not affect (P>0.05) Lm or APC growth during 91 days of 4C storage.
Conclusion Growth of Lm and APC were reduced
with higher nitrite concentrations and lower percent pump, while salt type did not affect Lm growth during 4°C storage.
Effect of Salt and Salt Replacements
on Listeria monocytogenes
Growth in a Broth System
Nigel Harper, Ph.D. candidate
Objectives To determine the effect that different
salts have on the growth of L. monocytogenesNaClKClCaCl2MgCl2Replacement saltSea salt
Materials and Methods Four chemical salts [sodium chloride
(NaCl), potassium chloride (KCl), calcium chloride (CaCl2) and magnesium chloride (MgCl2)] and two industrial salts (replacement salt and sea salt) at 0.5%, 1%, and 2.5.
Listeria enrichment broth used in this study was made without the sodium chloride and dipotassium phosphate.
Results
Results showed that MgCl2 actually induced growth (P > 0.05) compared to control (no salt) and other salt solutions.
The industrial salts both yielded greater (P > 0.05) populations than the controls.
These results show that replacing pure NaCl with a salt that contains magnesium could cause outgrowth of Lm.
Next Steps
Effect of salts on ground beef, ground turkey, and ground pork
Effects of salts in more complex meat systems
Acknowledgements
Dr. Elizabeth Boyle Dr. James Higgins Dr. Ann Brackenridge, Cargill Meat
Solutions Bruce Barry, Oberto Sausage Company Kim Uppal, Oberto Sausage Company Tyler Axman Shayne Lobaton-Sulabo Nigel Harper Tawnya Roenbaugh Dr. Melissa Weber
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