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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