Thermal Preservation/Processing of Foods Ch 19

Objectives To explore : Scientific principles behind thermal processing in home and industry Terminology used to describe thermal preservation Conduction versus convection heating Packaging used for thermally processed foods

Thermal Preservation/processing of Foods Refers to controlled processes that are performed commercially Blanching Pasteurizing Commercial Sterilization Inactivate disease and spoilage causing microorganisms Inactivate enzymes in food that can cause spoilage Increasing severity of the process

BLANCHING Type of process: Mild intensity heat process Exposes fruit / vegetables to boiling water OR steam for a short period of time ( 2 sec to 2-3 min)

BLANCHING Preservation effect: INACTIVATES endogenous enzymes Enzymes that can brown, wilt, etc. Drive off oxygen and other gases ( minimize pressure build up) Short term shelf life extension Combined with other forms of processing…. Canning and freezing

Pasteurization Louis Pasteur 1864 Type of Process: moderate intensity heat process Temperature below boiling point of water 80-90o C (176-194o F) Eg) Milk 15 sec at 72oC (162oF)- high temperature, short time HTST (flash pasteurizer) Process performed PRIOR to packaging

Pasteurization Preservation effect: Depend on on the type of food 1) low acid foods (milk, eggs) To destroy pathogenic ( disease causing) bacteria and viruses To inactivate enzymes 2) acid foods (beer, wine, fruit juices) Extend product shelf life Destroy some spoilage-causing microorganisms and enzymes Acid foods are not expected to be a source of pathogens… Except E. coli 0157:H7 Pasteurized vs unpasteurized juices * Primary reason- get rid of enzymes to extend shelf life.

Pasteurization Many spoilage-causing Microorganisms can survive Especially in low acid foods Combined with other forms of processing like refrigeration Moderate shelf life extension “Best if used before date” at less than or equal to 4oC “Intermediate heat treatment”

Commercial Sterilization (CS) Type of Process: high intensity heat process Also known as “canning” Cans, bottles, bags Requires a minimum of 121oC (250oF) moist heat for 15 minnutes

Commercial Sterilization Preservation Effect: Destroys spoilage causing and disease causing microorganisms Free from viable forms of microorganisms (including SPORES) Ensures spores of Clostridium botulinum are destroyed’ Bot. destruction not done on other two methods Aka: old term “ botulism cook”

Commercial Sterilization What does survive is a small number of heat resistant spores Do not cause disease Ex) extreme thermophiles ( like basillus bacteria) BUT are able to multiply (germinate) in the food product even if it is held at room temperature

Commercial Sterilization (CS) Performed once the food is packaged in suitable containers Containers must withstand high temperatures High pressures (sterilization is done in the container it is stored in) Must be hermetically sealed Impermeable to gas and liquid and microorganisms CS products have a long shelf life ( 2 years or more) Eg) canned products

UHT processing and Aseptic Packaging= Commercial Sterilization 1. Ultra High Temperature (UHT) Injection of hot steam under pressure (140-150oC; 284-302oF) for a short time (4-6 sec), followed by immediate cooling 2. Aseptic packaging- UHT food is aseptically placed into presterilized containers and sealed in aseptic environment Eg. Shelf stable milk

UHT processing and Aseptic Packaging UHT treated & aseptically packaged Shelf life > 6 months, w/o refrigeration ( more likely to breach seal of container) Some UHT treated foods are not necessarily aseptically packaged…. Not commercially sterile Longer shelf at refrigeration temperatures Not shelf-stable ( at room temperature) ****** Post processing recontamination

Commercial Sterilization Survivor Curve or Thermal Death Rate Curve (TDRC) (speed at which microorganisms are killed) If a given temperature kills 90% microbial population in the 1st minute of heating, 90% of remaining population will be killed in the 2nd minute, 90% remaining in the 3rd…. 10,000 start 1,000 1D 100 2D 10 3D 1 4D 0.1 5D Logo rhythmic order of death 1 log=90% or 10% survive If a food contains 10,000 mo, How many survivors will there be if A 3D process is applied? 10 4-3= 101= 10

Do the math…. How would you find the number of survivors after an application of a 3D thermal process to a food containing a starting microbial load of 1,000,000? Would the answer be….. A. 20,000 B. 5,000 C. 1,000 D. 100 E. 10 Death rate =90% per cycle/ log Each log survival = 10% or x .10 Math: log 1= 100,000 (90% survive) log 2= 10,000 (90% survive) log 3= 1,000 (90% survive)

Commercial Sterilization (CS) Survivor Curve or Thermal Death Rate Curves (TDRC) D-Value (decimal/ chemical reduction time) Time in minutes at a particular temperature (oC or oF) required to kill 90% of microbial population The more microbial load (microbes present) then the more logs (time) will be needed to reduce the number D-value = decimal reduction time

Thermal Death Curve Used to determine cooking time and temperature needed to kill a specific microorganism The lower the temperature the greater the exposure time needed to kill * Not necessarily sterile, but kills 90% of the population of specific microbe

Why is this important?????

What do these charts tell you?

Survivor curve (TDRC) One log cycle Thermophilic spores Population C. Botulism spores Vegetative state

Determine the thermal process required for different microorganisms of concern based on: Thermal Death Time Curves (TDTC) Times required for destruction of microbe under specific conditions at different temperatures Z-value (oC or oF) and F- value (minutes)

Z- value In the real world we don’t have instantaneous heat to 240oF Product may already be “ cooked “ at 220o F Z-value allows comparison of heating processes at different temperatures

Z-value= resistance of a microorganism to different temperatures D-value= time needed at a constant temperature to kill 90% of microorganism population Z-value= resistance of a microorganism to different temperatures The temperature change causes the 1 log cycle change in the Dvalue (it takes time for the change to happen) F-value = minutes required to kill microorganisms at a certain temperature

Heating time in “D-value” minutes F-value temperature If it takes an increase of 20oF for the D-value to change 1 log (90% death), then D-value slope =20oF

Now what do these charts tell you?

How can we determine if C.botulinum spores have been destroyed? 1. inoculated pack studies Clostidium sporogens PA3679 Spoilage causing microorganisms (anaerobic, spores) More heat resistant than spores of C. botulinum 2. Margin of safety (MS)

Margin of Safety (MS) MINIMIZE possibility of viable C. botulinum spores 1. Low acid foods – use a 12D thermal process (MS) 12D = 12 log cycle reduction= can kill 1012 (1 trillion) Microorganisms No food exists that has 1012 spores Large margin of safety ( usually large # of microbes< 1012 ) How much time required for the thermal process? Depends on the D value decreases as temperature increases

Margin of safety 2. acid foods- use a 5D thermal process/ or 3D C. botulinum will NOT grow in acid foods ( pH below 4.6)

Other factors that need to be controlled: (related to the FOOD constituents) Mechanism of heat transfer Consistency of the food ( solid, vicious liquid, a combination) Cold point- last area to heat in container Chemical composition of the food (eg. Fat, protein, …) Can act as insulators

Type of heat transfer (related to the Food constituents) Combination Like corn, beans and peas Solid foods Like canned tuna a salmon Non-vicous liquids Like broth or milk Conduction heating – transfer from molecule to molecule in straight lines Convection heating– transfer from fluid motion. Fluid heats along walls and rises

….. Effect of food constituents Sugars, starches, fats and proteins can protect spores & vegetable cells from the killing effect of heat D194 for salmonella in chocolate milk = 78 min (90% of salmonella) Chocolate milk has other ingredients D194 for salmonella in regular milk = 0.00008 min Also effect the heat transfer mechanism Other constituents may decrease the resistance of microorganisms to thermal processes. Eg.) acids, spices, some antimicrobial components

Types of packaging for thermally processed foods Cans (2-3 piece) Retort(able) pouches Tetrapak Glass jars or bottles Plastic

Commercial processing concerns: Safety- destroy harmful bacteria Quality- destroy organisms and maintain quality Cost- packaging,equipment and energy use, shelf life, shipping -

Heating food before or after pkg Either enclosed or conveyor belts Retort- huge pressure canners page 579 Pressure sealed to hold canned foods Still retorts- Like home pressure canners, limited temp 250oF Agitating retorts- gentle agitation

Retortable pouch 3 layers ( laminate) A. mylar or polypropylene outside surface B. aluminum – barrier to gases and water vapor; Hermatic container C. polypropylene- in contact with the food; inert (prevent contact of food with aluminum) heat resistant surface