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Conceivably Hazardous Food: The Evolving Definition of Temperature Control for Safety

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  1. Potentially Hazardous Food: The Evolving Definition of Temperature Control for Safety By Don Zink, PhD Lead Scientist – Food Processing Office of Plant and Dairy Foods Center for Food Safety and Applied Nutrition U.S. Food and Drug Administration and Shirley B. Bohm, RS, MPH Consumer Safety Officer Office of Compliance, DCP, Retail Food Protection Center for Food Safety and Applied Nutrition U.S. Food and Drug Administration NEHA Annual Educational Conference, June 26, 2005

  2. Food Preservation and Potentially Hazardous Food • Food safety is constantly evolving: 1825 – U.S. patent granted for preserving food in tin cans 1890 – Commercial pasteurization of milk 1908 – Sodium benzoate approved as a food preservative 1917 – Frozen foods available at retail 1962 – “PHF” is defined as perishable food that supports the rapid and progressive growth of infectious or toxigenic microorganisms 1976 – 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 containers 1993 – Added toxin production of C. botulinum; growth of SE in eggs; non-acidified garlic-in-oil; shell eggs; cut melons; raw seed sprouts 2005 – 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)

  3. Potentially Hazardous Food • Why 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 defined • The slow growth of low infectious dose pathogens such as Listeria monocytogenes was not considered • Water activity of 0.85 as a level of safety against Staphylococcus aureus was conservatively low • pH 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

  4. Potentially Hazardous Food • Why 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 alone • There is concern about the use of the word “hazard” which is used in a different manner in HACCP

  5. Potentially Hazardous Food • Why 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 food • Intrinsic factors of the food support the growth of bacterial pathogens • Nutrients • Energy source (sugars, alcohols, amino acids) • Nitrogen source (amino acids) • Vitamins and growth factors • Minerals • Available water (aw ), acidity (pH), redox potential (Eh). etc. • Epidemiological evidence associates food with foodborne outbreaks

  6. Sliced/Diced Tomatoes • Not heat-treated to destroy spore formers • Not treated with any other anti-microbial process • pH is < 4.6 • aw is > 0.99 • Considered PHF unless a product assessment proves otherwise

  7. Cut Melon • Not heat-treated to destroy spore formers • Not treated with any other antimicrobial process • pH of melons; • Honeydew pH = 6.3 – 6.7 • Watermelon pH = 5.2 – 5.6 • Cantaloupe pH = 6.2 – 7.1 • aw is > 0.99 • Considered a PHF unless a product assessment proves otherwise

  8. Dye Infiltration in Cantaloupe Photo courtesy of Dr. Michelle Smith, FDA/CFSAN

  9. Dye Infiltration in Cantaloupe Photo courtesy of Dr. Michelle Smith, FDA/CFSAN

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

  11. Raw Seed Sprouts • Not heat-treated to destroy spore formers • Not treated with any other antimicrobial process • pH is > 6.5 • aw is > 0.99 • Considered a PHF, unless a product assessment proves otherwise

  12. Potentially Hazardous Food • Why are some foods considered non-PHF? • If the food’s pH ≤ 4.6, it is below the pH at which proteolytic Clostridium botulinum can grow and produce toxin: • Because of inherent acidity – fruits • Because of acid from bacterial activity – fermented sausages, fermented milks, sauerkrauts, pickles • Because of acidification – added vinegar • If the food’s 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 bacteria • Low aw increases the length of the bacterial lag phase and decreases the growth rate

  13. PotentiallyHazardous Food • Which foods are considered non-PHF? • Unopened containers of hermetically sealed containers are “commercially sterile” • Foods 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 Preservatives • Other barriers/hurdles to pathogenic growth • A combination of barriers/hurdles to inhibit pathogenic growth

  14. Examples of Non-PHF/Non-TCS Food • Air-cooled, hard boiled egg – shell intact • Shell eggs treated to destroy all SE – pasteurized shell eggs • A 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

  15. Interaction Tables • The “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 considered • The effect of packaging which prevents re-contamination is considered • When tables indicate “Product Assessment Required” (PA), the food must be treated as PHF/TCS Food until laboratory evidence shows otherwise • Tables 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 FDA’s Foodborne Pathogenic Microorganisms and Natural Toxins Handbook (Bad Bug Book) at http://www.cfsan.fda.gov/~mow/factors.html

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

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

  18. Other Factors AffectMicrobial Growth • Other 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 *USDA’s Pathogen Modeling Program can be downloaded at http://www.ars.usda.gov/Services/docs.htm?docid=6784

  19. Interaction Table A

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

  21. Interaction Table B

  22. When to Use Interaction Table B • Table 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 Assessment • Food not heat-treated may contain vegetative cells and pathogenic spores • Food that was heat-treated but not packaged may become re-contaminated • pH values considered in Table B must include 4.2 because Staphylococcus aureus can grow at that level

  23. Use of aw/pH Interaction Tables Decision Tree Is the food heat-treated? No Yes Is the food treated using some other method? Is it packaged to prevent Recontamination? Yes No Yes No Further product assessment (PA) or vendor documentation required Using the food’s known pH &/or aw values, position the food in the correct table

  24. Use of aw/pH Interaction Tables Decision Tree Using the food’s known pH and/or aw, position the food in the appropriate table Use Table A (heat-treated and packaged) Use Table B (not heat-treated or heat- treated but not packaged) Non-PHF/non-TCS Food may be held out of temperature control and is considered shelf stable Product Assessment Further product assessment or vendor documentation required Non-PHF/non-TCS Food may be held out of temperature control and is considered safe from bacterial pathogens Product Assessment Further product Assessment or vendor Documentation required

  25. Application of Interaction Tables • Preliminary questions: • Is the food held refrigerated for quality, not safety – NOT enforceable – What is the scientific basis? • Consider the food’s safety history – if not associated with foodborne outbreaks, scientific rationale should be able to explain • Any 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 equipment • aw value – homogenous sample with calibrated equipment • Heat-treatment must destroy vegetative cells • Packaging must be sufficient to prevent recontamination • Product 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

  26. Application of Interaction Tables - Parmesan Cheese • Parmesan Cheese: • aw = 0.68 – 0.76 • pH = 6.5 • curd heated to ~ 130°F & cured 2-3 years, then packaged • Ambient storage desired & no history of related illness • The food is heat-treated/cured & packaged • Using this information, Table A is chosen • Locate the cheese’s aw (0.68 – 0.76) in the correct line and pH (6.5) in the correct column • They intersect at “Non-PHF/Non-TCS” • No temperature control is required

  27. Application of Interaction TablesAmerican Process Cheese Slices • American Process Cheese Slices • aw = 0.94 – 0.95 • pH = 5.5 – 5.8 • Heat processing and packaged to retail • Ambient storage desired for 24 hrs. • Cheese is heat-treated and unpackaged • Table B is chosen because it may become recontaminated • Locate the cheese’s aw (0.94 – 0.95) in the correct line and pH (5.5 – 5.8) in the correct column • They intersect at PA – Product Assessment Required • Challenge testing with 4 pathogens at 86°F showed no growth for 24 hrs. and no growth for 210 days when refrigerated

  28. Application of Interaction TablesSushi Roll with Raw Fish • Sushi roll with raw fish: • Cooked rice: • aw = 0.98 – 0.99 • pH = 6.0 – 6.7 (acidified rice pH = 4.2) • Raw fish: • aw = > 0.99 • pH = 5.2 – 6.1 (tuna), 6.1 -6.3 (salmon), 6.8 – 7.0 (shrimp) • Ambient temperature display desired for buffet line • Only rice, not fish is heat-treated & not packaged • Locate the food’s aw and pH in the correct line and column • They intersect at PA – product assessment required • The food is PHF unless reformulated in some way • If 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 discarded • If the sushi roll with raw fish was packaged for retail sale, Table B is still used because of the raw fish

  29. Evaluation of Laboratory Evidence • When is laboratory evidence likely to be used? • Variance application • Performance standard • Preservatives added • New technologies used • pH and aw Interaction Tables say “PA” – Product Assessment Required • Multi-ingredient or combination foods with two or more distinct food components - the interface may have different properties than either of the individual ingredients

  30. Evaluation of Laboratory Evidence • Microbiological challenge testing • Design, implementation and assessment must be done by an EXPERT MICROBIOLOGIST • Failure to account for a specific product or environmental factors in the design could result in a flawed conclusion • A competent laboratory should be used to conduct the challenge testing

  31. Evaluation of Laboratory Evidence • What factors should be considered in designing a challenge study?* • Selection of challenge organism(s) • Level of challenge inoculums • Inoculums preparation and methodology • Duration of the study • Formulation factors and storage conditions • Sample 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