High and low temperatures

Factors affecting microbial development Intrinsic factors Nutrients pH Redox water activity antimicrobial constutuents Extrinsic factors Temperature Gaseous environment humidity Implicit factors Growth rate Microbe-microbe interactions Stress responses Processing factors Food preparation Pasteurization Non-thermal methods

Mechanisms of preserving foods ProcessFactors Preservatives (acids, etc)Antimicrobials Vacuum packagingGaseous environment MAP, CAPGaseous environment Pasteurization/appertisationTemperature Freezing, chillingTemperature, a w Drying, curingawaw EmulsificationCompartmentalization RadurizationIonizing radiation High pressure processingPressure Other non-thermalDiverse mechanisms

Effects of freezing Nucleation and crystal growth Freezing rate affects this composition Physical damage to microorganisms – Denature enzymes – Damage membranes

Temperature and water activity

Temperature-water activity Osmotic pressure greater on inside To balance this, water flow is into cell Creates positive turgor pressure (pressure pushes out on cell membrane) Hypotonic (normal situation) Where does water start to freeze?

Process of freezing Ice crystals form in extracellular environment Reduced vapor pressure outside, water flows intra- to extracellular environment Increases intracellular ion concentration Rapid vs. slow freezing

Factors affecting effect of freezing Cryoprotectants – Glycerol – Corn syrup – Sucrose – Proteins including: Albumin Gelatin “Anti-protectants” – Sodium chloride

Effect of thawing Freezing may damage food as well Breaking down biological structures Return to favorable temps Nutrient release Organisms gain access

Heat processes ProcessTemperature Cooking<=100 o C Blanching<100 o C Drying<100 o C Pasteurization60-80 o C Appertisation>100 o C

Pasteurization Often applied to dairy products, but anything can be pasteurized Milk: – Originally designed to eliminate Mycobacterium tuberculosis, Coxiella burnetti – Low temperature, long time (LTLT) 63 °C (145°F), 30 min, vat pasteurization – High temperature, short time (HTST) 72°C (161°C), 15 sec – Ultrahigh temperature (UHT) °C, 1-2 sec

Aseptic packaging Often >130 o C Packaged in sterile containers Less energy, often improved quality No cold chain needed

Microbial Standards for Milk Standard Milk for Raw Consumption Milk for Pasteurization Pasteurized Milk Bacteria count≤20,000 cfu/mL≤100,000 cfu/mL≤ 20,000 cfu/mL Coliform count≤ 10 cfu/mLno standard≤ 10 cfu/mL Somatic cell count ≤1,000,000 cells/mL ≤ 750,000 cells/mL Grade A ≤ 1,000,000 cells/mL Manufacture Grade N/A Pathogen count000

Microbial issues in milk Psychrotrophs and LAB Bacillus cereus – Spore forming (D 100C ) = min – Sweet curdling – Bitty cream Clostridium tyrobutyricum – Spore forming (D 80C )= 13 min – Late-blowing – Lactate  butyrate + acetate + CO 2 + H 2

Appertisation (canning) Nicholas Appert High heat, hermetically sealed Clostridium botulinum (D 121C ~ 0.2 min) – 12 D concept for low acid foods Commercially sterile – Misnomer – Can achieve by heat and other factors

F-value Mostly applied to canning Way of comparing heat processes Using D and Z values, what is kinetics of inactivation at 121 o C? F 121 or F o = D 121 Example: D 101 = 10 minutes; Z = 10 o C, – F o = 0.1 minutes

Growing trend/concern