Presence of Antimicrobial Compounds in Poultry

Rinsate Samples

June 5, 2013

1

Introductions Dr. Scott Russell—Presenter

Professor of Poultry Science, University of GA Over 200 publications including “Controlling Salmonella in

Poultry Production and Processing”—new text book Internationally known industry consultant

Dr. Jon Howarth—Presenter Ph.D. Physical Chemistry, University of Southampton, UK VP Technology, EnviroTech Chemical Services Over 26 patents in disinfection technologies

Support Dennis Smithyman, President, Adv. Food Technologies Bob Hibbert, Partner, Morgan & Lewis

2

Presentation Outline Issue summary Historical background

Use of Buffered Peptone Changes in intervention strategies

No change in USDA sampling procedures Current situation

Excess chemical carryover into rinsates Proper neutralization chemistries

Examples Options/recommendations for USDA

3

Issue Summary Historically, USDA poultry samples were pulled

immediately after the Chiller and rinsed in buffered peptone

Any pre-chill chemical intervention, like an OLR, would be washed off the carcasses and diluted in the chillers

Thus, there was no significant chemical carry-over into the rinsate sample bag

Any minor chemical carryover was neutralized by the Buffered Peptone Based on the intervention chemicals and use levels

approved at that time

4

Issue summary

Today, USDA-FSIS poultry samples are pulled after the post-chill chemical intervention without any change to the original USDA sampling protocol

The high chemical concentrations in these new “finishing chillers” and “deluge cabinets” can sometimes overcome the sampling dilution effect and remain active in the rinsate These chemicals can continue to kill the pathogens free-

floating in the sample, while shipped overnight to the lab The lab ends up reporting false negatives and therefore

shows better results than are actually being achieved on the carcasses

5

1990’s Mega Regs/HACCP rule Established in 1996 with a phased-in

implementation schedule Set Salmonella Performance standards Sampling procedures immediately after the chiller

Establishment of No visible fecal/ingesta rule Subsequent Approval of OLR waiver

Brought new chemistries into the field Pre-chill intervention No detrimental effect on sampling procedures Chemical completely removed during chilling

(processing aid) 6

Chemical interventions by early 2000’s Chillers

Chlorine + Acidified Chlorine at 1-50 ppm Cl PAA up to 30-40 ppm

OLR TSP up to 5% solution Sanova (ASC) 500-1200 ppm Cl Chlorine dioxide 3 ppm residual Acid blends 1.4-2.0 pH Cecure (CPC) 0.8% maximum spray followed by

a potable rinse or chiller immersion 7

Original USDA sampling point post chiller

Scalders Chillers Pickers Evis NYD Rehang IOBW OLR

Fresh Water

Chlorine Mixer

Mixer

Low PAA or Chlorine ppm

High level Antimicrobial

Chemical

USDA Sample point

No Antimicrobial Residual as per “processing aid”

status

8

USDA Poultry Sampling Procedure

Aseptically pull a carcass Let drip – time not specified Place in sterile bag Add 400 ml Buffered Peptone Water (BPW) 30 shakes – approx 60 seconds Transfer to cup and refrigerate Package for shipment Ship overnight to the lab

9

Peptone Poultry Rinsates post chill Peptone is a source of organic nitrogen and cultivates

microorganisms by supporting nutritional requirements It is a water-soluble ingredient derived from enzymatically

digested pork, beef or milk products Also contains fats, metals ions, salts, vitamins and other

biological compounds Low ppm levels of oxidizer chemistries in the chillers or chiller-

diluted OLR chemistries (absent finishing chillers) are further diluted in the 400ml solution

At these levels the buffered peptone completely deactivates those chemistries and eliminates risk of interference with subsequent microbiological testing The exception is CPC, which is not neutralized, but is

diluted well below effective levels, when it is used upstream as an OLR chemistry

10

USDA OLR study data On the USDA-FSIS web site is a summary of 11

chemistries that were collected from their approval submissions for OLR

The report nicely summarizes that, on average, the chemistries reduced APC’s by roughly 0.8 log10 and reduced Salmonella incidence by 10%

A review of the individual data from each of the chemistries would show a relatively close band of performance around this average (0.5-1.5 log10 reductions) except for Cecure (CPC)

11

USDA OLR Study

12

Other studies—Oklahoma State It can be concluded that a reasonably good chemistry in a

standard spray cabinet can achieve a 0.5-1.5 log10 APC reduction

A “deluge” cabinet or equivalent dip could possibly achieve slightly better performance

A broad study that would be conducted across a wide range of chemistries under the same operating conditions (pressures, flows, and contact time) using the chemical manufacturer’s recommended concentrations would show a similar range, but no “silver bullet” Such a study was conducted on beef surfaces by Oklahoma State

University under a protocol approved by USDA The results were similar to the OLR comparison with most good

chemistries between 0.5-1.5 log10 reductions Important to Note that Cecure was in the bottom half of

performance 13

OSU Ross Study

14

Oklahoma State Protocol 2 in diameter beef sirloin wafers to be passed through a Ross

spray bar system Ambient temperatures, chemicals sprayed at 1.5 gal/min Chemical concentrations determined by the manufacturer E.coli O157:H7 inoculated with an average of 6 log10

Specific recoverable resistant variants to ensure no false readings

Samples stomached with DE Neutralizing broth Dilutions made in 0.1% buffered peptone water for plating

Samples not plated immediately were held in bags in the refrigerator, then DE Neutralizing broth added prior to microbial processing

Sampling times at 1 hr, 1 day, 7 days, and 14 days Demonstrate effect on meats held at processor or in-transit

15

Immediate Results Shows the Relative Effectiveness of

the tested Products—0.3-1.5 log10 reductions 24 hr results showed most chemistries at 0.6 - 2.0 log10 reductions Cecure at 0.8 log10 reduction after 24 hr

16

New Multiple Hurdle Concept

As performance standards tightened over the decade, the concept of multiple hurdles took hold

Even as new chemistries were being approved, it was clear there were no “silver bullets”

A 1 log10 reduction in APC was considered a good intervention by most studies and industry experts in the field

Thus, to meet the tightening standards, a processor must install several interventions along the line

The objective is to reduce at every process point Including immediately following the chiller

17

Actual Log10 Aerobic Plate Count (APC) CFU/mL of rinse on broiler carcasses during processing

0 1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 Pre-scald Post-pick Pre-IOBW Pre-OLR Pre-chill Post-chill Post-Fin chill Log 1

0 APC

CFU

/mL

of c

arca

ss ri

nse

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Typical log10 Salmonella Count CFU/mL of rinse on broiler carcasses during processing

0

0.5

1

1.5

2

2.5

1 2 3 4 5 6 Pre-scald Post-scald Post-pick Pre-OLR Pre-chill Post-chill

Log 1

0 Sal

mon

ella

CFU

/mL

of c

arca

ss ri

nse

19

Actual Log10 Campylobacter Count CFU/mL of rinse on broiler carcasses during processing

0

0.5

1

1.5

2

2.5

3

3.5

1 2 3 4 5 Pre-NYD Post-Evis Sub Tank

Pre-OLR Pre-Chill Post-Chill

Log 1

0 Cam

py C

FU/m

L of

car

cass

rins

e

20

Multiple Hurdle Today

Even as new chemistries were being approved, it was clear there were no “silver bullets”

A 1 log10 reduction in APC is considered a good intervention

USDA-FSIS therefore accepted industry petitions that a chemical intervention post-chill (i.e. finishing chillers) would be acceptable Permitted sampling after the post-chill intervention No change in the sampling procedure

Still essentially the 1998 procedure

21

Multiple Interventions with Post Chiller Treatment and USDA Sample Point

Scalders Chillers Pickers Evis NYR Rehang IOBW OLR Post-

Chill

Fresh Water

Antimicrobial #1

Mixer

Mixer

PAA or Chlorine

Antimicrobial #2

USDA Sample Point

Mixer

High Antimicrobial Residual

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Current USDA approvals for finishing chillers (commonly used chemicals)

Cecure (CPC) concentration up to 0.8% by weight (8000 ppm) Followed by an unspecified water rinse (spray)

PAA up to 2000 ppm Usually used at 750-1200 ppm

Sanova (ASC) up to1200 ppm Chlorine reading usually 800-1000 ppm

Acid blends down to 0.5 pH Usually used at 1.0-1.8 pH

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Finishing chiller microbial performance

At these listed (approved) levels many of these chemistries can be found in the rinsate at a high enough level to continue to kill bacteria and therefore create false negatives

Let’s review each of the listed chemicals and some studies Listed in order of greatest concern first

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USDA OLR study data—Cecure (CPC) Previously mentioned: A review of the individual

data from each of the chemistries shows a relatively close band of performance around this range of 0.6-1.5 log10 APC reductions except for Cecure (CPC)

Cecure’s submitted data claimed log10 reductions over 4.0 log10 APC and all “zeros” for Salmonella incidence

Personal and practical experience indicates that this extraordinary result was due to a failure of the rinsate to effectively neutralize the active chemical CPC

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USDA OLR Study

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Cecure test in an OLR cabinet Dr. Russell conducted a plant-wide validation study for a

submission to USDA in May, 2005 The plant had failed the USDA sets, installed new interventions

and needed a full plant–wide assessment The new OLR intervention was a Cecure deluge spray cabinet

No water rinse was required because the birds then went into the chiller

SafeFoods provided the recommended neutralization chemistry (charcoal)

Meanwhile, Dr. Russell was overseeing the implementation of CPC as an OLR agent at another facility

The net reduction was 2+ log10 APC and a 60% drop in Salmonella prevalence—good, but not 4+ logs and “zeros” as in the USDA data set

In the second plant, CPC achieved a 10% reduction in Salmonella 27

Info on PAA There are several producers of PAA Historically, it was approved as a spray or dip up to

230 ppm Over time, this chemical breaks down to a non-reactive

state, especially in the presence of organic matter Thus, there had not been an obvious carryover of this

chemistry However, in 2011-2012, the USDA approved FMC’s

Spectrum PAA as a poultry dip at levels of up to 2000ppm Usage at 800-1200ppm is now common

The following PAA bag test was a simple lab experiment to demonstrate potential for chemical carryover 28

Info on PAA Testing was done to determine the carry-over from rinsed chicken

carcasses that could cause a PAA residual left in the Rinsate samples being sent to a lab for testing

The testing was done as follows A 3.9 lb bird and a 5.8 lb bird were initially placed in three (3) gallons of

water for thirty seconds. Various hang times were allowed and then, the carcasses were placed in a

dry bag to drain The amount of water remaining in the bag after the bird was removed was

then measured The results were as follows: Water Run Off (In ml)- Hang Time 3.9# Bird 5.8# Bird Immediate 310 370 10 Seconds 38 104 One Minute 11 26

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Info on PAA

Carcasses ranging in size from 5.72 to 6.18 lbs were placed in various PAA ppm solutions for a period of 30 seconds Those birds were then given hang times from immediate to one minute prior to placing in bags The birds were then "shaken" for 60 seconds in 400 ml buffered Peptone with no additives Titrations were done on the bath and on the Buffered Peptone rinsate after being poured into a standard specimen cup used for shipping to the lab

30

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Info on PAA We did not test as high as permitted, but the testing clearly

shows that at these elevated ppm levels, there is chemical carryover While the PAA may dissipate over 18-24 hours, it is

killing for a long time in refrigeration or transit The data also shows that hang time is very important for

this chemical treatment If the QA person (not USDA under SIP) throws the carcass

quickly into the bag and does not allow for a full minute of drip time, then there is significant carryover As these plant QA people are usually not supervised at

the sampling point, we have often observed they will not wait at all and certainly not for a full minute

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Info on Sanova (ASC) Sanova is approved at a 2.5-2.9 pH and up to 1200 ppm of active chlorine The Buffered Peptone will raise the pH, but high concentrations of active

chlorine compounds will continue to kill in the cup in a post-chill dip XXXXX Poultry Co. specifically utilizes Sodium Thiosulfate to neutralize

any chlorine based chemistry. However, most other poultry companies do not neutralize Sanova.

Ecolab prepared a study gathering various plant biomap studies where Ecolab had one or more products as interventions. The testing was done at each plant by the local Ecolab rep Several of the plants were in the XXXXX Poultry Co. system

Plants 3, 5, and 6 all used Sanova ASC in a post-chill dip at roughly the same operating conditions. Microbiologists would therefore expect similar reductions at all 3

locations. However, plant # 5 showed a greater than 3 log10 (99.9%) reduction

The other two plants had 0.8 and 1.6 log10 reductions, which are more typical results for post-chill dips and would indicate neutralization

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Sanova in a Post–Chill Dip

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Importance of Neutralization According to Johnston (2002), “For accurate

assessment of surviving organisms following contact with a disinfectant, the activity of the disinfectant MUST be arrested at the moment of sampling.”

“In early studies on disinfection, efficacy was often

over-estimated due to poor, or no, neutralization of the disinfectants after a specified time of exposure to the bacteria.”

35

Neutralization of Poultry Rinsates Many poultry companies are aware finishing chiller

chemical carryover can distort the microbial results of the sampling procedure

Properly run poultry companies make the correction, even if the USDA does not require it

For example, XXXXX Poultry Co. requires a neutralization step in the cup as quickly as possible. Their internal protocol (including SIP plants) specifically lists a neutralization step for each intervention chemistry

However, even XXXXX Poultry Co. may not be adjusting for the new levels of some chemicals in these finishing chillers and post chill “deluge” spray cabinets

36

Neutralization of Poultry Rinsates Moreover, most companies just use the USDA-FSIS

method and are pleased that this shows “good results”

As companies and USDA move to SIP, the USDA-FSIS will rely on these internal evaluations

Is it any wonder that the USDA-FSIS data shows the slaughter plants are doing well, but parts are not doing well (Salmonella 26%, Campylobacter 21%) Salmonella infections in the population have not shown

the expected decrease like E. coli O157:H7 on beef The new Poultry Parts regulations will have the same

testing problem if a neutralization step is not added to the procedure

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Neutralization of Poultry Rinsates

If the USDA were to consider adding a rinsate neutralization step (like XXXX Poultry Company), what would be a possible neutralization chemistry?

Let’s review in order of least difficult to most difficult: Low pH acids Low levels of Halogens ASC + Chlorine Dioxide PAA Cecure (CPC)

38

Low pH Acid Blends

This group includes any approved acid blend that kills strictly by low pH

This includes Hydrochloric + Citric acid blends under trade names Syntrx, FreshFx,

and Citrilow Sulfuric acid blends Aftec and Super SAS

The USDA method uses 400ml Buffered Peptone, which usually has enough buffering capacity to neutralize the acid and keep the rinsate above 5+ pH (above the kill range)

However, some plants run split samples and start with Butterfields, which has less buffering capability Thus there is killing in the cup until the sample is split and the Peptone

is added The QA person is to test the rinsate with a pH strip and raise the pH to

above 6.0 with the NaOH before shipping to the lab 39

Halogens Chlorine and Bromine are approved at relatively low levels

and the dilution effect or organic material in the rinsate reacts with these halogens sufficiently to minimize any kill in the cup

The more active forms of chlorine, specifically Chlorine Dioxide and Acidified Sodium Chlorite (Sanova) are a different matter

Sanova is approved for use at a 2.5-2.9 pH and up to 1200ppm of active chlorine

While the Buffered Peptone will raise the pH, the high concentration of chlorine could continue to kill in the cup

XXXXX specifically utilizes Sodium Thiosulfate to neutralize any chlorine based chemistry. However, the question is: “is that a sufficient amount?” Where are the studies to prove the neutralizer amount is

sufficient? 40

PAA Neutralization Peroxyacetic Acid (aka Peracetic Acid) is

composed of acetic acid, peracetic acid, and hydrogen peroxide in an equilibrium blend unique to each manufacturer

After application, this chemical breaks down to a non-reactive state, especially in the presence of organic matter

However, in higher concentrations this process takes a longer time

PAA can be neutralized with Sodium Thiosulfate, just like the halogens Again, the question is: “what level of neutralization will

ensure no kill in the bag?” 41

Cecure (CPC) Neutralization

Cetylpyridinium Chloride is a quaternary ammonium compound that does not breakdown (it endures)

It is therefore required to be rinsed off the carcass before the carcass or parts can go into the marketplace

The same applies to the poultry rinsate (Buffered Peptone) which cannot neutralize the CPC Thus, ANY carryover of this chemistry into the rinsate will

necessarily continue to kill pathogens while in refrigeration or transit to the lab

As Cecure is a large cationic (+) compound, a large anionic (-) compound is needed to neutralize it

42

Cecure Neutralization—large positive Cation needs a large negative Anion

43

Cecure neutralization per SafeFoods • Using a sterile poultry rinse bag, a whole bird is removed from the line thirty seconds

(or as long as possible) after the Cecure® spray cabinet • Any excess liquid is allowed to drain from the bird • Only complete carcasses with all the appendages and skin are sampled • 400 milliliters (ml) of Butterfield’s Phosphate Diluent (BPD) is poured into

the body cavity of the bird and over the outside of the bird • Using a 1 foot arcing motion, the bird alternating from one hand to the other

for approximately one minute, ensuring that the liquid flows in and out of the body cavity as well as on the outside of the bird

• The liquid is allowed to drain out of the body cavity The rinse is poured back into the original 400 ml jar

• NO TIME IS MENTIONED HERE From the original jar, 100 ml is poured into another jar containing 14 grams activated carbon

• The cap is replaced on the jar and gently inverted several times to completely neutralize antimicrobial activity of CPC NO PROOF OF NEUTRALIZATION

• The neutralized sample is placed on ice • The samples are sent to the lab for analysis

44

DEPARTMENT OF HEALTH AND HUMAN SERVICES Food and Drug Administration,21 CFR Part 173, [Docket No. 2006F-0409], Secondary Direct Food Additives Permitted in Food for Human Consumption, AGENCY: Food and Drug Administration, HHS. ACTION: Final rule.

One comment concerned an efficacy trial conducted by the petitioner in which carcasses were tested post-chiller and after neutralizing CPC on the treated carcasses with activated carbon. The comment expressed concern that bacteria may have been trapped by the activated carbon producing a ``false negative'' result for the treated carcasses.

However, the petitioner has stated that all 2,300 samples in the trial were ``neutralized'' with activated carbon whether or not the sample was treated with the CPC solution. What PROOF?

Thus, the available data confirm that the results from this efficacy study were not adversely affected by the use of activated carbon to neutralize CPC on the samples.

However, NO data were presented that proves CPC was being neutralized by the carbon. Only that it may be trapped. Interestingly, trapping CPC does NOT DEACTIVATE IT. 45

Neutralization Study •Bosilevac et al. (2004) conducted experiments using CPC to determine the methods of neutralization needed to obtain valid microbiological measurements

•The authors found that residual CPC in hide sponge samples prevented bacterial growth

•Dey- Engley neutralization media at 7.8% and a centrifugation step were necessary to overcome this problem

46

Dey Engley Neutralizing Broth Ingredients (g/L)

Casein enzymatic hydrolysate 5.00 Yeast extract 2.50 Dextrose 10.00 Sodium Thiosulfate 6.00 Sodium thioglycollate 1.00 Sodium bisulfite 2.50 Lecithin 7.00 Polysorbate 80 5.00 (surfactant) Bromocresol purple 0.02

47

Dey-Engley Neutralizing Broth

Complex media Carbon is not complex and does

not neutralize Simply absorbs CPC Is it 100%?

48

Micrograph of bacteria on chicken skin: Bacteria are protected from disinfection

49

•When bacteria are released into rinsate, they are surrounded by CPC and (artificially) reduced, when compared to reductions on actual skin •The TIME that this is allowed to happen is critical •No TIME LIMIT has been given in the protocol •In reality, ANY time is unacceptable •Dey-Engley broth should be used in the rinsate to prevent this situation

400 mL Rinsate

Carbon

CPC

CPC

CPC

CPC CPC

CPC

CPC

CPC

CPC

CPC

CPC

CPC

CPC

CPC

CPC

CPC CPC

CPC

CPC CPC

CPC

CPC

Diagram of the Problem

CPC can Continue Killing Bacteria 50

Neutralization Study 2 Osman et al. (2012) reported that, “The

results confirm that there is extended killing activity of residual CPC against Salmonella gaminara or Salmonella sonnei if the residual CPC remaining in contact with the lettuce after the initial 1-min wash is not quenched.”

51

Cecure chemical residues on carcasses + parts in the marketplace While generally outside the scope of this seminar on active

chemical residuals in the poultry rinsates, the issue of CPC residues on chicken carcasses and parts in the marketplace should be raised

Because CPC endures, the USDA requires processors to use a water rinse after the Cecure deluge cabinet Some SafeFoods sales people state to the processor that they only

need to “mist” the carcass to meet the USDA-FSIS requirement Some poultry processors specifically want to get some

“chemical in the cup” while sampling If the processor is sampling after the water rinse, then misting helps get

chemical into the cup USDA has recently given permission for processors to sample BEFORE the

water rinse under certain conditions

52

CPC Residues

From Morales et al. (2005), “From the evaluation of CPC residues in beef and chicken tissues it is evident that CPC residues levels are strongly influenced by the nature of the treated food surface or tissue. In particular, it has been demonstrated that CPC binds to proteins and fats…. we were anticipating lower residue levels that those observed in beef or chicken.”

53

CPC Residues

According to a study by Cutter et al. (2000), “However, residual CPC levels following any of the treatments were considered excessive for human consumption.”

54

Dr. Andrew Laumbauch Division of Petition Review, HFS-265 Office of Food Additive Safety Center for Food Safety and Applied Nutrition Health and Human Services FDA

The petitioner states that residual CPC activity was neutralized before enumerating surviving bacteria on the treated carcasses. This statement is not borne out by the detailed procedures included; no neutralizing agent is shown as being added to the recovery wash fluid (buffered peptone water) to stop the action of CPC on the surviving bacteria. 55

Response to that question

In Question 4, you requested information on the use of the neutralizing agent that is added to the recovery wash fluid (buffered peptone water) to terminate the action of the CPC on the surviving bacteria. While it was not mentioned in the study report, the Petitioner has confirmed that the CPC activity was neutralized using D/E Neutralizing Broth (International BioProducts), a common neutralizing agent for use with quaternary ammonium compounds.

56

D/E Neutralizing Broth Composition per liter: Glucose/Dextrose: 10.0g Lecithin: 7.0g Sodium Thiosulfate Pentahydrate: 6.0g Polysorbate: 80 5.0g (surfactant) Pancreatic digest of casein: 5.0g Sodium bisulfite: 2.5g Yeast extract: 2.5g Sodium thioglycollate: 1.0g Bromcresol Purple: 0.02g Sodium thiosulfate Pentahydrate neutralizes halogens and oxidizers such as

peracetic acid Sodium bisulfite neutralizes formaldehyde and gluteraldehyde Sodium Thioglycollate neutralizes mercurials Lecithin neutralizes quaternary ammonium compounds and biguanides Polysorbate 80 neutralizes phenols, hexachlorophene, and formalin Lecithin with Polysorbate 80 this combination neutralizes ethanol

57

Question

Why did SafeFoods use DE Neutralizing Broth in the original approval submission to FDA and now recommend Carbon Filtration?

58

Summary of Discussion USDA poultry samples are pulled after the post-chill chemical

intervention but without any change to the original USDA sampling protocol

that pulled them after the chiller The high chemical concentrations in “finishing chillers” and

“deluge cabinets” can overcome the dilution effect and remain active in the rinsate These chemicals can continue to kill the pathogens while in the

overnight shipment to the lab The lab ends up reporting false negatives and therefore shows

better results than are actually being achieved on the carcasses The risks with the current system:

High risk product going into the marketplace Poultry processors who now neutralize will stop under SIP The same sampling problem will carryover into the new parts regs

59

Recommendations to USDA Confirm our results

Laboratory testing of chemistries Inoculated studies on carcasses Inoculated studies on parts

Require all approved chemical intervention providers to submit neutralization recommendations These recommendations need to be supported with

independently validated studies Require the chemical suppliers provide the needed

neutralization chemistries to the poultry industry and the USDA staff at each processing plant These need to be in easy sample sizes and sufficient quantities to

ensure there is no disruption in testing plans USDA needs to assess existing and planned

performance standards and timelines Any procedure change needs to be phased in so that the majority

of the industry can meet the goals within a reasonable timeframe

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References Bosilevac, J. M., T. L. Wheeler, M. Rivera-Betancourt, X. Nou, T. M. Arthur, S. D.

Shackelford, M. P. Kent, D. Jaroni, M. S. Osborn, M. Rossman, J. O. Reagan, and M. Koohmaraie, 2004. Protocol for evaluating the efficacy of cetylpyridinium chloride as a beef hide intervention. Journal of Food Protection, 67(2):303-309

Cutter, C. N., W. J. Dorsa, A. Handie, S. R. Morales, Z. Zhou, P. J. Breen, and C. M. Compadre, 2000. Antimicrobial activity of cetylpyridinium chloride washes against pathogenic bacteria on beef surfaces. Journal of Food Protection, 63(5):593-600

Johnston, M. D., R. J. W. Lambert, G. W. Hanlon, and S. P. Denyer, 2002. A rapid method for assessing the suitability of quenching agents for individual biocides as well as combinations. Journal of Applied Microbiology, 92:784-789

Morales, S. R., X Zhou, H. Salari, R. Casilo, P. J. Breen, and C. M. Compadre, 2005. Liquid chromatography determination of residue levels on apples treated with cetylpyridinium chloride. Journal of Chromatography A, 1062:285-289

Osman, M., M. E. Janes, R. Story, R. Nannapaneni, and M. G. Johnson, 2006. Differential killing activity of cetylpyridinium chloride with or without bacto neutralizing buffer quench against firmly adhered Salmonella gaminara and Shigella sonnei on cut lettuce stored at 4 degrees C. Journal of Food Protection, 69(6):1286-1291

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