Lecture 7: Thermal processing Flashcards
What is thermal processing?
Severe heat treatments; canning as well as-
mild heat treatments pasteurization and balancing.
What are the 3 goals of food preservation?
- Minimize food spoilage
- Maximize safety and stability
- Optimize nutritional value and acceptability
What was the origin of Thermal processing?
Nicolas Appert (1750-1841) was the first to establish industrial thermal processing of foods.
What was Louis Pasteur’s contribution to thermal processing?
(1822-1895)
Microbes spoil wine, beer, and milk.
Developed pasteurization.
Why is thermal processing a effective food preservation and sterilization technique?
Bacteria are susceptible to heat.
Additionally, enzymes and oxidative changes are also inhibited
What is canning?
Canning is a severe heat treatment.
Generally 110 - 121 C for 15min
How is canning achieved?
Achieved using retort?
What is the goal of canning?
the destruction of all pathogens.
Although some extremeophiles may still remain within the canned environment.
How long dose the average canned food product last?
A 2-year shelf-life is achieved.
What are the 3 factors to consider when establishing how much heat to apply during thermal processing?
- Type and size of container used
- Heat transfer ability of the food
- microbial heat reistance
What is conduction?
heat transferred from molecule to
molecule via molecular collisions
What is convection?
Heat transferred through a liquid which circulates.
What is the main consideration when heating up objects?
Heat must get to the “cold spot” in the can.
What is the difference between the molecular moment of conduction and convection?
Conduction: molecule to molecule in straight lines
Convection: molecules move in fluid motion.
Is there a size limit to the size of the can that can be thermally processed?
Yes there is.
What is the thermal death-time curve?
This curve provides data on the destruction of a specific microbe at different temperatures.
What is a D value?
Decimal reduction time
What is the D Value?
A unit used to describe the heat resistance of microbes.
What do D values represent?
D values represent the time needed to destroy 1 log cycle (90%) of the bacteria present.
What is an example of a D value?
D100 = 2 min
or
S. aureus D71.7 = 4.1 second
What are D values used for?
Used to calculate process time in the food industry.
How many Log cycle reductions are needed in the food industry?
12
What are two things to think about when determining what D value we should use?
- depends on the specific organisms present
2. Depends on the number of organisms present
What is the standard target organism within the canning process?
- Bacillus stearothermophilus for canned foods
* These spores are more heat resistant than C. Botulinum
What is the probability that a can would have a botulinum spore within it?
1/1000000000000
Bacteria are killed most easily within what environment?
High heat, and high acid conditions.
Is the process of sterilization different in naturally acidic foods?
Lower temperatures and shorter times can be used.
What are the danger zones?
4-60 C (lots of pathogen growth)
What are examples of mild heat treatments?
Pasteurization and blanching.
What are the aims of mild heat treatments?
- Kill pathogens
- Reduce bacterial count; food is not sterile
- inactivate enzymes
What are the advantages of mild heat treatments?
Minimal nutritional and palatability changes
What are the disadvantages of mild heat treatment?
Short shelf life
additional processing method is required (refrigeration or freeing)
What is pasteurization?
Used to process beverages and liquid
What happens during pasteurization?
Pathogens are destroyed but some spoilage microbes will still remain.
What happens to enzymes during pasteurization?
They becomes inactive
What additional preservation methods are used to
enhance shelf life of pasteurised products?
refrigeration
When is blanching used?
Used prior to freezing for vegetables and some fruit.
What is the role of blanching?
Inactivates enzymes that would cause off-odours and offcolours during frozen storage.
what is blanching?
Vegetables are immersed in boiling water for a few
minutes
What is the result of blanching?
“reduces the microbial load”; does not create a
commercially sterile product
How is radiation used to sterilize and preserve food?
Radiant energy comes from electromagnetic waves, microwaves are most common within this feild.
Water molecules in a food are excited by microwaves.
What is the advantage of microwave perseration?
Microbes are killed at far lower temperatures than conventional processes?
true or false:
Irradiation is a ____ process.
cold
What type of radiation is used in radiant energy processing?
ionizing radiation.
How common is the use of irradiation in the food industry?
it is limited to only some foods and specific purposes
What is the purpose of irradiation?
- pathogen destruction
- Spoilage inhibition
- longer shelf-life of fruits and vegetables by slowing ripening and sprouting.
What is cold pasteurization?
an alternative to thermal
pasteurisation.
• High physical pressure for 5-20 minutes destroys
microbes
are microb spores destroyed within cold pasteurization?
no
What is the benefit of cold pasteurization?
Product nutritional and sensory properties are preserved.
When would cold pasteurization work best?
Works best on high moisture products, not dry products or
those with air pockets.
What is cold pasteurization a example of?
High Pressure Processing (HPP)
What is HPP applied to?
HPP is applied to fresh juices, meats, prepared products.
What is the focus of hurdle technology for food preservation?
Safe and fresher foods within minimal affect on the food quality.
What is the method of application for hurdle technology for food preservation?
a series of preservative factors that the target
microorganisms are not able to overcome.
such as available water ,pH, temp, and chemical antimicrobials
How are Hurdles applied?
The combination of hurdles are chosen specifically for each food.
Are all hurdles applied at the same level?
Individual hurdles may be set at lower concentrations/intensities
than would be required if only a single hurdle was used as the
preservation technique.
