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Formulating Foods for Microbiological Safety. Kathleen Glass, Ph.D. Assistant Scientist Food Research Institute University of Wisconsin-Madison President-Elect International Association for Food Protection BAFP 21 November 2003 Florianópolis Brasil. Formulation-safe foods.

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Formulating foods for microbiological safety

Formulating Foods for Microbiological Safety

Kathleen Glass, Ph.D.

Assistant Scientist

Food Research Institute

University of Wisconsin-Madison


International Association for Food Protection

BAFP 21 November 2003

Florianópolis Brasil

Formulation safe foods
Formulation-safe foods

  • Definition of low acid (canned) foods

  • Risks to consider

  • Strategies to formulate safe foods

    • Refrigerated foods

    • Shelf-stable foods

    • Convenience foods

      • Meet changing needs of consumers “on the go”

Low acid foods
Low acid foods

  • pH > 4.6 and aw >0.85

    • Considered potentially hazardous if not refrigerated

  • United States: Low Acid Canned Foods

    • Assumed to be shelf-stable

    • Hermetically sealed container

    • Often process-safe

      • Inactivate microorganisms of public health significance

      • “Retort” thermal processing; commercially sterile

    • Primary concern: Clostridium botulinum

    • Must file process with FDA

      • Including all imported foods

Formulation safe foods1
Formulation-safe foods

  • Acid or acidified foods pH < 4.6

  • Foods with water activity < 0.85

  • Low acid foods with multiple barriers

    • Combination of pH, aw, antimicrobials

    • Recommend formulating certain refrigerated foods for safety to control psychrotrophic bacteria ex. Listeria

Goal for formulating safe foods
Goal for formulating safe foods

  • General rule: < 1-log increase of pathogen for time that is 1.5X shelf life as determined by manufacturer

    • Must be bacteriostatic

  • Processed meats

    • No more than 1-log increase of LM during shelf-life

  • Other shelf-stable foods

    • No botulinal toxin production 2x shelf-life

  • Need to consider whole food, individual components, and interfaces of components

Risk analysis
Risk analysis

  • Pathogens

    • Type and level of contamination likely in raw ingredients and environment

      • Infectious dose

      • Growth vs. survival

      • Thermal stability of pathogens

      • Recontamination potential

  • Presence of competitive microflora and expected shelf-life

Risk analysis1
Risk analysis

  • Storage temperature

    • Shelf-stable vs. refrigerated

    • “Traditional” vs. novel storage

      • Modified atmosphere packaging

    • Temperature control during distribution

    • Risk of temperature abuse at retail and with consumers

  • Consider worse case scenario

  • Reevaluate if formulation changes

Do not rely on temperature alone to protect foods
Do not rely on temperature alone to protect foods

  • Pasteurization is not perfect

    • Spore survive pasteurization

    • Post-pasteurization contamination

  • Temperature abuse is common

    • During distribution, at homes, power-outages

  • Growth of psychrotrophic pathogens

    • Listeria monocytogenes

    • Nonproteolytic C. botulinum

    • Some Bacillus cereus strains

Pathogens of concern the big 5
Pathogens of concern:“The Big-5”

  • Clostridium botulinum

  • Listeria monocytogenes

  • Staphylococcus aureus

  • Enterohemorrhagic E. coli

  • Salmonella

Other pathogens of concern
Other pathogens of concern

  • Clostridium perfringens

  • Bacillus cereus

  • Campylobacter

  • Parasites and viruses

  • Control by:

    • Same formulation strategies as for “The Big-5”

    • Good manufacturing and good agricultural practices

    • Proper heating/cooling

    • Employee hygiene

Foods of concern
Foods of concern

  • Foods that support growth of select pathogens at refrigeration temperatures

  • Low acid foods with traditional storage at room temperature

  • High risk foods that can be formulated for enhanced safety

    • Refrigerated processed meats

    • Refrigerated foods / entreés with heat treatment

    • Process cheese products

    • MAP bakery products

    • Garlic-in-oil; herbs-in-oil (fresh; not pre-acidified)

Acid and water activity
Acid and Water Activity

  • Gram-negative bacteria: acid tolerant

    • Salmonella, Enterohemorrhagic E. coli survival pH <4.0

    • Seldom grow at aw <0.95

  • Gram-positive bacteria: salt and aw tolerant

    • S. aureus

      • Growth at aw 0.86

      • Enterotoxin production ~ 0.91

    • L. monocytogenes

      • Growth at 0.92

    • C. botulinum

      • Growth at 0.93

    • Minimal pH for growth 4.5 – 5.2 depending on acidulant

Useful antimicrobials
Useful Antimicrobials

  • Phosphate based emulsifiers

    • C. botulinum in process cheese

  • Antimycotics (sorbate, benzoate, propionate)

    • S. aureus, C. botulinum, L. monocytogenes

  • Organic acid salts (lactate, diacetate)

    • C. botulinum, L. monocytogenes in meats/other foods

  • Nitrite (US usage 80-156 ppm)

    • C. botulinum, L. monocytogenes in meats

  • Lysozyme (400 ppm in cheese)

    • Clostridium sp.

  • Bacteriocins/nisin (250 ppm in cheese)

    • Bactericidal against gram-positive bacteria

  • Temperature

  • Acidity

  • Water activity

  • Antimicrobials

  • Competitive microflora

  • Proper fermentation

  • Nutrient availability

  • Oxygen content

Hurdle Technology

Critical aw values

Critical pH values

4.6 or less

>4.6– 5.6


0.92 or less


Temperature Controlled for Safety











Control of spores

Product treated to control vegetative cells and protected from recontamination.

Critical aw values

Critical pH values


4.2 – 4.6

>4.6– 5.0

> 5.0

< 0.88





0.88– 0.90















Control of vegetative cells and spores

Product not treated or treated

but not protected from recontamination


40 ppm NO2

pH 5.3

Aw 0.975

L. monocytogenes

USDA-ARS Pathogen Modeling Program 6.0


40 ppm NO2

pH 5.9

Aw 0.99

Examples of formulation safe foods
Examples of Formulation-Safe Foods

Formulating processed meats
Formulating Processed Meats

  • Safety by good manufacturing practices and formulation

    • Clostridium botulinum

      • Proteolytic vs. nonproteolytic

    • Listeria monocytogenes

    • Staphylococcus aureus

    • Clostridium perfringens

    • Enterohemorrhagic E. coli

    • Salmonella

Control strategies for processed meats

Sodium lactate

Sodium diacetate

Sodium nitrite





Organic acids


Other antimicrobials

Control Strategies for Processed Meats

Fermented dried sausage
Fermented dried sausage

  • Reduced pH and aw

  • Fermentation

    • Organic acids – primarily lactic acid

    • Bacteriocins

    • Competition for nutrients

  • Nitrites

  • Effective against LM, C. bot, S.aureus

  • E. coli O157:H7 reduction usually requires heat

E coli and l monocytogenes
E. coli and L. monocytogenes

AEM 58:2513

JFP 52:226

Refrigerated high moisture processed meat formulations
Refrigerated High-Moisture Processed Meat Formulations

L. monocytogenes, 4°C

Glass and Doyle, AEM, 1989

Effect of temperature and antimicrobials
Effect of temperature and antimicrobials

Glass et al, 2002, JFP 65:116

Effect of lactate and diacetate
Effect of lactate and diacetate

Glass et al, 2002, JFP 65:116

Formulating process cheese shelf stable
Formulating Process Cheese(Shelf-Stable)

  • pH 5.4-6.0

  • Aw 0.94-0.96 cheese spread

  • Aw 0.91-0.93 cheese slices

Controlling c botulinum in process cheese spreads



Total salts


Phosphate-based emulsifier

Water activity not accurate predictor of safety if 0.93-0.96

Applicable to spreads with >51% cheese; 20-25% fat

Controlling C. botulinum in process cheese spreads

Tanaka et al, 1986

S aureus process cheese
S. aureus, process cheese

Glass et al., Unpublished data, 2001

20 formulations – 2 lots each, 27C

Refrigerated cooked potatoes control c botulinum ph a w temp
Refrigerated cooked potatoes:Control C. botulinum pH/aw/temp



Chicken broccoli sauce entre control c botulinum by ph lactate
Chicken-broccoli-sauce entreéControl C. botulinum by pH/lactate

Map pizza crusts control c botulinum a w ph sorbate
MAP Pizza CrustsControl C. botulinum aw/pH/sorbate

 supports toxin production

Ono toxin production

Products contained 0.3% sorbic acid

Fresh pasta control c botulinum a w ph
Fresh PastaControl C. botulinum aw/pH

Check individual


*supports toxin production

ºno toxin production



What not to rely on for safety
What NOT to rely on for safety

  • Finished product testing for pathogens

  • Proper handling and refrigeration

  • Modified atmosphere packaging

  • Pasteurization or irradiation alone

Rely on
Rely on:

  • Secondary barriers

  • GMPs and environmental controls


    • Responsible for 70% decline in listeriosis

  • Good source of ingredients

  • Proper and clear labeling

    • Code dating


Use or discard in 7 days after opening

Refrigerate after opening

Use by…

How to start
How to start

  • Predictive modeling

    • ARS Pathogen Modeling Program 6.0


    • Purac OptiForm Listeria Control Model

    • FRI model for process cheese

  • Published results for specific foods

  • Verify with challenge testing

Formulation safety depends on many factors
Formulation Safety Depends on Many Factors

  • Consider all sources of contamination

    • Assume pathogens are present in raw ingredients/environment

    • Use high-quality raw materials with low levels of microorganisms

    • Reduce/prevent levels of contamination by proper sanitation/heat treatment

Formulation safety continued
Formulation Safety…continued

  • Multiple hurdles

    • Synergistic interaction means that lower of each factor can be used

    • Consider effect of competitive microflora

    • Assure that manufacturing specifications are met

    • Control storage temperatures wherever possible

  • Educate consumer with clear code dates and storage conditions on labels

For additional information

For additional information:

Kathleen Glass, Ph.D.

Assistant Scientist

Food Research Institute

University of Wisconsin-Madison

1925 Willow Drive

Madison, Wisconsin 53593 USA

E-mail: [email protected]

Phone 608.263.6935; Fax: 608.263.1114


  • [NACMCF] National Advisory Committee on Microbiological Criteria for Foods. 1998. Hazard analysis and critical control point principles and application guidelines. J Food Prot 61:762-75.

  • [NSF] NSF International. 2000 Nov. 10. Non-potentially hazardous foods. Ann Arbor (MI): NSF International. Report nr ANSI/NSF 75-2000. 12 p.

  • IFT Status Summary, Extended Shelf Life Refrigerated Foods: Microbiological Quality and Safety, Vol. 52. Feb. 1998.