Thermal Death Flashcards
What is the difference between pasteurization and sterilization?
Pasteurization only reduces #
Sterilization KILLS ALL.
What are some ways to extend shelf life?
- Reduce the increase of microorganisms
- Use pH, preservatives, drying, radiation.
Use of:
1. Bacteriostatic stops active growth
2. Bactericidical kills microbes
What are examples of bacteriostatic?
Freezing, osmotic pressure, desiccation and pH
What are some examples of bactericidal?
Heating, radiation, chemical. Sterilization
Bactericidal is meant for?
Spores and cells. Kill by baking, boil, frying or microwave. Exceeds 100C
What is the purpose of cooking? (at what temp)
< or = 100C to enhance flavor
What is the purpose of blanching?
<100C removes oxygen, destroys enzymes (not cooking b/c not held long enough at the temp, still kills enzymes)
Drying/ concentration
<100C Removes water, extends storage life.
Pasteurization
60-80C Kills target pathogens and spoilage microorganisms. Kills all vegatative cells, but spores are still pressent.
Sterilzation
> 100C Kills all microorganisms, including spores. (Use pressure to go over 100C).
What are the benefits of heath processing?
Cheap, quick, easy, may improve flavor (cooking), may inactivate undesirable enzymes ( blanching), enhances storage life of a product (drying), inactivation of pathogens and spoilage organisms (pasteurization).
Heat treatments: A few things about it.
Organisms specific sensitivity ( in a given environment
Rate of killing is log
Function of temp an time
For a time and temp there’s a constant % destroyed.
When performing heath processing caculations it’s good to know a few things like…
Concentration of microorganisms,
acceptable concentration of microorganisms that can survive
Thermal resistance of target organisms (most heat tolerant, establish temp requirements)
TIME AND TEMP relationship required for destruction.
1 log cycle is?
The time and temperature it takes to decrease the population by 90%. (from log 6 to log 5)
Thermal death is a ………….cycle.
log linear cycle
- given a specific time interval and temperature, the same % of population will be destroyed, regardless of population present.
What does a log cycle tell you if you have the time required to destroy one log cycle (90%), and you know the desired thermal reduction (# log cycles) it tells you…
The time it will take for you to get to the # of logs required.
If # of microorganisms increase, heating time will also have to increase..why?
To bring the time down to an acceptable level.
D value!!!!
DOES NOT MEAN SLOPE OR RATE
Expressed as time ( decimal reduction time)
Time to decrease Microbial population by 1 log (90%) at a given temp in a given system.
Explain when D would change?
Depends on species,Aw, composition of food (fat stabilized it), and temperature used. It tells u the sensitivity of an organism to heat treatment.
D90= time
D90 means at 90C and the smaller the D value, the quicker the orgnaisms will die
D90=10min
D90=1min
The second one means that there is a reduction of 1 log in 1 min, and the top one means there is a reduction of 1 log in 10min.
How does the composition of food affect D?
Fat and CHO increase the resistance of the microorganism. ex. Salmonella spp. D70 6-8hr in chocolate milk 10seconds in low fat milk
FAT STABILIZES!
D100 of 5 min.
explain after 5 min, 10 min and 15min
5min reduced by 90% (1 log)
10min reduced by 99% (2 log)
15min reduced by 3 logs
What does Canning use for d value?
12D process
12 times.
D value caculations ex. rate of inactivation= 1.5log/5min rate=slope= rise/run= y/x= log CFU/time Rate=log CFU/time 1.5log/5min=1/x x=1/(1.5log/5min) x=3.3min D=3.3min
Shown on previous slide.
Z value..what is it?
Expressed as temperature
It’s the change in temperature required for a thermal destruction curve to decrease one lo cycle in the same amount of time.
( relates to resistance of microorganism)
z value in simple terms?
Change in temperature for 1 order of magnitude larger or smaller killing rate.
Z value
- Rate of killing is temperature dependent.
- For a given system everything is constant EXCEPT time and temp.
- Determined by the SLOPE of the thermal deat htime curce d value vs temperature
Keeping going, you got this.
What is Z value dependent on?
Strain, and chemical composition of media
Changing z value by 5C means?
That it kills factor of 10x faster.
ex. At 100C originally needs 20 min.
What about at 105C and 95C
At 105 need 2min (for same rate of kill)
at 95 need 200min ( for same rate of kill)
- Worry about temp at which the microorganism will grow such as the danger zone 4.4-60C
F value?
Time to reudce populaion by given amount in autoclave conditions ( 121C, 3psi)
F0= Dr(loga-logb)
Dr= D value at temp 121C
a= initial population ( # of cells)
b=final population
ex. Dr=0.45 initial population= 10^6 Final population = 10^1 F0=.45(log10^6-log10^1) F0=.45(6-1) F0=2.25min
DEATH KINETICS
Usually plotted linear… however not in real conditions (done in plants!)
Shouldering and tailing
What is shouldering? What causes it?
Shouldering is a lump at the start of the graph rather then linear.
It is causes by not even heating, clumping of organism so they are not evenly exposed to the heat.
What is tailing and what causes it?
It is a tail of the graph and is caused by more resistant mutatnts, heat shock proteins.
What is heat shock proteins?
Exposure to high temp for a short time could be induced. A stress response that allows cells to develop greter reistance to subsequent heat treatment.
Heat shock proteins
seen at 60-70C, killed at 140C
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(____________ kind of graph.
cell injury ( sublethal injury)
Occurs when heating injures cell but doesn’t kill it.
- Inability to grow in selective media ( doesn’t have the resources)
- give time, restore viability and extend the lag phase.
- STORAGE ALLOWS FOR REPAIR OF CELLS (BAAAAD)
Sterilization..what is it?
Heating > 100C KILLS ALL CELLS, including endospores.
UHT (ultra-high temperature) 130C for sec (better on nutritional value)
Sterilization 121Cfor 15-20min
What is the most resistant to sterilization?
Prototype.
bacillus stearothermophilus
Kill endospores at Dr 4 to 5min
Pasteurization..what is it?
<100C
reduced numbers to safe levels
kill problem organisms
What microorganisms are dangerous in milk?
Mycobaterium tuberculosis (pathogen) - D65.6 for 0.2-0.3min
coxiella burnetii
- Resistant to chemical and physical treatment.
D65.6=0.5-0.6min
What are the two types of pasteurization?
LTH (Low temp holding) 63C for 30min
HTST (high temp, short time) 72C for 15sec
What is an indicator organism in pasteurization?
Alkaline phosphatase
_ If not prsent we’ve killed pathogens we wanted to.
Z value similar to heath resistant pathogens.
What is the process times of cooked meats?
Most pathogens killed if internal temp at >71C
- Heating removes natural flora (stabilizes food)
- Nitrites often included if meat stored anaerobically.
