Potentially Hazardous Food: The Evolving Definition of Temperature Control for SafetyByDon Zink, PhDLead Scientist Food ProcessingOffice of Plant and Dairy FoodsCenter for Food Safety and Applied NutritionU.S. Food and Drug Administration

andShirley B. Bohm, RS, MPHConsumer Safety OfficerOffice of Compliance, DCP, Retail Food ProtectionCenter for Food Safety and Applied NutritionU.S. Food and Drug AdministrationNEHA Annual Educational Conference, June 26, 2005

Food Preservation and Potentially Hazardous FoodFood safety is constantly evolving:

1825 U.S. patent granted for preserving food in tin cans1890 Commercial pasteurization of milk1908 Sodium benzoate approved as a food preservative1917 Frozen foods available at retail1962 PHF is defined as perishable food that supports the rapid and progressive growth of infectious or toxigenic microorganisms1976 Added crustacea and synthetic ingredients to definition, Exempted foods with pH 4.6; aw 0.85; clean, uncracked shell eggs; food in unopened, hermetically sealed containers1993 Added toxin production of C. botulinum; growth of SE in eggs; non-acidified garlic-in-oil; shell eggs; cut melons; raw seed sprouts2005 Added TCS Food as an equivalent/transition term for PHF, pH and aw Interaction Tables, and consideration for pathogenic microorganisms instead of only Clostridium botulinum and Salmonella Enteritidis (1-201.10 in FDA Food Code)

TCS Food stands for Time/temperature control for safety food.Both the terms will be retained in the Food Code for several editions to assist in the transition from PHF to TCS food.

Potentially Hazardous FoodWhy is the definition of potentially hazardous food changing in the Food Code?

The rapid and progressive growth of infectious and toxigenic microorganisms" in the old definition was not clearly definedThe slow growth of low infectious dose pathogens such as Listeria monocytogenes was not consideredWater activity of 0.85 as a level of safety against Staphylococcus aureus was conservatively lowpH of 4.6 may also be inappropriate as Listeria monocytogenes grows at 4.39, Salmonella spp. at 4.2 and Yersinia enterocolitica at 4.2 BUT pH 4.6 is appropriate when only spore forming pathogens are present

FDA submitted an issue to the 2004 Conference for Food Protection recommending this change in the definition of Potentially Hazardous Food. The issue was based on an IFT report, Evaluation and Definition of Potentially Hazardous Foods, found at http://www.cfsan.fda.gov/~comm/ift4-toc.html, which recommended certain changes. FDA contracted with IFT to do the evaluation.

Potentially Hazardous FoodWhy is the definition of potentially hazardous food changing in the Food Code?

Sufficient research has been done on food products to construct tables that predict the growth of pathogenic microorganisms when the interaction of both pH and aw are considered (See Tables A & B)Many factors control or prevent the growth and toxin production of foodborne pathogens besides pH and aw aloneThere is concern about the use of the word hazard which is used in a different manner in HACCP

Potentially Hazardous FoodWhy are some foods considered PHF?

PHF/TCS food means a food that requires T/T control for safety to limit pathogenic microorganism growth or toxin formation

No or inadequate hurdles to pathogenic bacterial growth in the foodIntrinsic factors of the food support the growth of bacterial pathogens

Nutrients Energy source (sugars, alcohols, amino acids)Nitrogen source (amino acids)Vitamins and growth factorsMinerals Available water (aw ), acidity (pH), redox potential (Eh). etc.Epidemiological evidence associates food with foodborne outbreaks

Sliced/Diced TomatoesNot heat-treated to destroy spore formersNot treated with any other anti-microbial processpH is < 4.6aw is > 0.99Considered PHF unless a product assessment proves otherwise

Cut MelonNot heat-treated to destroy spore formersNot treated with any other antimicrobial processpH of melons;Honeydew pH = 6.3 6.7Watermelon pH = 5.2 5.6Cantaloupe pH = 6.2 7.1aw is > 0.99Considered a PHF unless a product assessment proves otherwise

Dye Infiltration in Cantaloupe

Photo courtesy of Dr. Michelle Smith, FDA/CFSAN

Dye Infiltration in CantaloupePhoto courtesy of Dr. Michelle Smith, FDA/CFSAN

Dye buildup on canker(rind blemish)Photos courtesy of Dr. Michelle Smith, FDA/CFSAN

Raw Seed SproutsNot heat-treated to destroy spore formersNot treated with any other antimicrobial processpH is > 6.5aw is > 0.99Considered a PHF, unless a product assessment proves otherwise

Potentially Hazardous FoodWhy are some foods considered non-PHF?

If the foods pH 4.6, it is below the pH at which proteolytic Clostridium botulinum can grow and produce toxin:

Because of inherent acidity fruitsBecause of acid from bacterial activity fermented sausages, fermented milks, sauerkrauts, picklesBecause of acidification added vinegar

If the foods aw 0.85, it is below the water activity at which Staphylococcus aureus grows and produces toxin:

Not enough water is available for metabolic activities of pathogenic bacteriaLow aw increases the length of the bacterial lag phase and decreases the growth rate

Potentially Hazardous FoodWhich foods are considered non-PHF?

Unopened containers of hermetically sealed containers are commercially sterileFoods with laboratory evidence showing that T/T control is not required AND the food contains:

A preservative to inhibit pathogens see 21 CFR 172 Subpart B, Food PreservativesOther barriers/hurdles to pathogenic growthA combination of barriers/hurdles to inhibit pathogenic growth

Examples of Non-PHF/Non-TCS FoodAir-cooled, hard boiled egg shell intactShell eggs treated to destroy all SE pasteurized shell eggsA food that does not support the growth of pathogenic microorganisms even though they may be present (i.e., E.coli O157:H7 in apple cider or norovirus on crackers)Some foods that are refrigerated for quality, not safety

Interaction TablesThe hurdle effect is used several inhibitory factors used together to control or eliminate pathogens that would otherwise be ineffective when used alone The effect of a heat treatment which destroys vegetative cells is consideredThe effect of packaging which prevents re-contamination is consideredWhen tables indicate Product Assessment Required (PA), the food must be treated as PHF/TCS Food until laboratory evidence shows otherwiseTables A & B consider the interaction of pH and aw under certain conditions of heat-treatment and packaging

Refer to Factors Affecting the Growth of Some Foodborne Pathogens in FDAs Foodborne Pathogenic Microorganisms and Natural Toxins Handbook (Bad Bug Book) at http://www.cfsan.fda.gov/~mow/factors.html

Water Activity in FoodsWater activity (aw ) is the water in foods that is available for metabolic purposesaw = p / po (pure water is 1.00)Effect of aw on microorganismsMost spoilage organisms do not grow below 0.91Spoilage molds can grow as low as 0.80Staphylococcus aureus can grow as low as 0.86Clostridium botulinum can grow & produce toxin as low as 0.94Some parasites (Trichinella spiralis) survive at low aw Water activity ranges for growth are affected by temperature and nutrient levelsWater activity in a food can be changed by adding salt or sugar or by drying

Acidity in FoodspH is a measure of acidity in food using a scale of 0 to 14, with 7.0 being neutralMicroorganisms grow best in neutral or slightly acidic conditionsYeasts and molds can grow at pH 3.5Clostridium botulinum can grow and produce toxin as low as pH 4.7Staphylococcus aureus can grow at pH 4.2Listeria monocytogenes and Yersinia enterocolitica can grow down to pH 4.4The minimum pH for growth of microorganisms is dependent on many factors inherent acidity, type of acid, salt concentrationThe further out (above or below) the optimum pH for growth, the longer the lag phase will be

Other Factors AffectMicrobial GrowthOther factors affect the growth of pathogenic microorganisms besides pH and aw Redox potential (ease of transferring electrons in food during energy metabolism)Atmosphere within packaging (i.e., ROP)Antimicrobials and bacteriosins (i.e., nisin)If other factors besides pH and aw are used to show that the food is non-PHF, a pathogen modeling program* or laboratory evidence must be provided

*USDAs Pathogen Modeling Program can be downloaded at http://www.ars.usda.gov/Services/docs.htm?docid=6784

Interaction Table A

Table A. Interaction of pH and aw for control of spores in food heat-treated to destroy vegetative cells and subsequently packaged.aw ValuespH Values4.6 or less> 4.6 5.6> 5.60.92 or lessNon-PHF*/non-TCS**Non-PHF/non-TCSNon-PHF/non-TCS> 0.92 0.95Non-PHF/non-TCSNon-PHF/non-TCSPA***> 0.95Non-PHF/non-TCSPAPA* PHF means Potentially Hazardous Food** TCS means Time/Temperature Control for Safety Food*** PA means Product Assessment Required

When to Use Interaction Table ATable A can be used to determine if a food which is heat-treated and packaged is PHF, Non-PHF or Requires Product AssessmentFood must meet cooking requirements of Food Code section 3-401.11 (no partial cooks) to eliminate vegetative pathogensSpore forming pathogens are the only remaining biological hazards of concernFood is packaged to prevent re-contaminationTherefore, higher pH & aw can be safely tolerated

Interaction Table B

Table B. Interaction of pH and aw for control of vegetative cells and spores in food not heat-treated or heat-treated but not packaged.aw ValuespH Values< 4.24.2 4.6> 4.6 5.0> 5.0< 0.88Non-PHF*/non-TCS**Non-PHF/non-TCSNon-PHD/non-TCSNon-PHF/non-TCS0.88 0.90Non-PHF/non-TCSNon-PHF/non-TCSNon-PHF/non-TCSPA***> 0.90 0.92Non-PHF/non-TCSNon-PHF/non-TCSPAPA> 0.92Non-PHF/non-TCSPAPAPA* PHF means Potentially Hazardous Food** TCS means Time/Temperature Control for Safety Food*** PA means Product Assessment Required

When to Use Interaction Table BTable B can be used to determine if a food which is not heat-treated or heat-treated but not packaged is PHF, Non-PHF or Requires Product AssessmentFood not heat-treated may contain vegetative cells and pathogenic sporesFood that was heat-treated but not packaged may become re-contaminatedpH values considered in Table B must include 4.2 because Staphylococcus aureus can grow at that level

Use of aw/pH Interaction Tables Decision Tree

Is the food heat-treated?NoYesIs the food treated using some other method?Is it packaged to preventRecontamination?YesNoYesNoFurther product assessment(PA) or vendor documentation requiredUsing the foods known pH &/oraw values, position the food inthe correct table

Use of aw/pH Interaction Tables Decision Tree

Using the foods known pH and/or aw, position the food in the appropriate tableUse Table A(heat-treated andpackaged)Use Table B(not heat-treated or heat-treated but not packaged)Non-PHF/non-TCSFood may be heldout of temperature control and is consideredshelf stableProduct AssessmentFurther product assessment or vendor documentation requiredNon-PHF/non-TCSFood may be heldout of temperaturecontrol and isconsidered safe from bacterial pathogens Product AssessmentFurther product Assessment or vendorDocumentationrequired

Application of Interaction TablesPreliminary questions:Is the food held refrigerated for quality, not safety NOT enforceable What is the scientific basis?Consider the foods safety history if not associated with foodborne outbreaks, scientific rationale should be able to explainAny pH and aw values must be accurate and replicable from a competent laboratory

pH value chemistry grade pH paper accurate to 0.05 or calibrated equipmentaw value homogenous sample with calibrated equipmentHeat-treatment must destroy vegetative cellsPackaging must be sufficient to prevent recontaminationProduct assessment may result in a finding of non-PHF, limited shelf life or Time as a Public Health Control, required temperature control or reformulation of product

Application of Interaction Tables - Parmesan CheeseParmesan Cheese: aw = 0.68 0.76 pH = 6.5 curd heated to ~ 130F & cured 2-3 years, then packagedAmbient storage desired & no history of related illnessThe food is heat-treated/cured & packagedUsing this information, Table A is chosenLocate the cheeses aw (0.68 0.76) in the correct line and pH (6.5) in the correct columnThey intersect at Non-PHF/Non-TCSNo temperature control is required

Application of Interaction TablesAmerican Process Cheese Slices

American Process Cheese Slicesaw = 0.94 0.95pH = 5.5 5.8Heat processing and packaged to retailAmbient storage desired for 24 hrs.Cheese is heat-treated and unpackagedTable B is chosen because it may become recontaminatedLocate the cheeses aw (0.94 0.95) in the correct line and pH (5.5 5.8) in the correct columnThey intersect at PA Product Assessment RequiredChallenge testing with 4 pathogens at 86F showed no growth for 24 hrs. and no growth for 210 days when refrigerated

Application of Interaction TablesSushi Roll with Raw FishSushi roll with raw fish:Cooked rice:

aw = 0.98 0.99pH = 6.0 6.7 (acidified rice pH = 4.2)Raw fish:

aw = > 0.99pH = 5.2 6.1 (tuna), 6.1 -6.3 (salmon), 6.8 7.0 (shrimp)Ambient temperature display desired for buffet lineOnly rice, not fish is heat-treated & not packagedLocate the foods aw and pH in the correct line and columnThey intersect at PA product assessment required

The food is PHF unless reformulated in some wayIf room temperature display (for 4 hrs.) is desired, TPHC can be used if a marking system is used and any left after 4 hrs. is discardedIf the sushi roll with raw fish was packaged for retail sale, Table B is still used because of the raw fish

Evaluation of Laboratory EvidenceWhen is laboratory evidence likely to be used?Variance applicationPerformance standardPreservatives addedNew technologies usedpH and aw Interaction Tables say PA Product Assessment RequiredMulti-ingredient or combination foods with two or more distinct food components - the interface may have different properties than either of the individual ingredients

Evaluation of Laboratory EvidenceMicrobiological challenge testingDesign, implementation and assessment must be done by an EXPERT MICROBIOLOGISTFailure to account for a specific product or environmental factors in the design could result in a flawed conclusionA competent laboratory should be used to conduct the challenge testing

Evaluation of Laboratory EvidenceWhat factors should be considered in designing a challenge study?*

Selection of challenge organism(s)Level of challenge inoculumsInoculums preparation and methodologyDuration of the studyFormulation factors and storage conditionsSample analysis

*For more information, refer to Ch. 6 in Evaluation and Definition of Potentially Hazardous Food at http://www.cfsan.fda.gov/~comm/ift4-toc.html

TCS Food stands for Time/temperature control for safety food.Both the terms will be retained in the Food Code for several editions to assist in the transition from PHF to TCS food.

FDA submitted an issue to the 2004 Conference for Food Protection recommending this change in the definition of Potentially Hazardous Food. The issue was based on an IFT report, Evaluation and Definition of Potentially Hazardous Foods, found at http://www.cfsan.fda.gov/~comm/ift4-toc.html, which recommended certain changes. FDA contracted with IFT to do the evaluation.