Week11C1-2 : thermal processing Flashcards
What are the three basic levels of heat treatment?
- Sterilization
- commercial sterility
- Pasteurization/blanching
What is the temperature of sterility and the time
121˚C for 15 minutes.
What is the definition of sterility?
means there is no living forms alive or biologically active
What is the definition of commercial sterility ?
kill all pathogenic and toxin-forming vegetative organisms.
at what temperature is steam if under these pressure :
10 psi :
15 psi :
20 psi :
10 psi : 116
15 psi : 121
20 psi : 127
T or F : for low acid foods, the temperature of the food needs to reach temperature higher than 100C
t
T or F : the temperature used in pasteurization are over the boiling point
f
T or F : the pasteurization and the commercial sterility deactivate spores
false, the pasteurization doesn’t deactivate spores but the commercial sterility does
What is the goal of blanching
To denature the enzymes that are deleterious in fruits and vegetables
What are the three rules that decides the thermal processing that will be done?
- eliminating the microorganisms
- Maintaining the nutritional and sensory qualities
- Food safety
T or F : C. Botulinum is used to evaluate the efficacy of a thermal processes
F, it is too dangerous because it is a dangerous spore and you need to use the more temperature resistant spores
What are the two spore former used to evaluate the efficacy of thermal processing
- Clostridium sporogenes PA3679
2. Bacillus stearothermophilus
What is the commercial sterility levels of spores in cans
10^-6 (or 12 log reduction or 12D)
What is the D-value?
the deciml reduction time is the heating time required at a given temperature to reduce the microbial population by one log unit.
How is the D-value determined
by experimentation of standard plate count of samples that have been heated for different amounts of time
What is the thermal death rate curve?
The curve that shows the log reduction of spores against the time for a specific temperature
Does temperature affect the thermal death curve?
yes.
What is the Z value?
It is the thermal resistance of an organisms and depends on the d-value. The temperature increase corresponding to reduce the D value by one loge or 10 factor
What does HTST stands for ?
high temperature short time
What are the two types of thermal processing?
- conventional processing
2. Aseptic processing
What is the type of thermal processing that is suitable for the HTST processes
aseptic processing
What is the name of the machine used that is a large pressure cooker
batch retort.
T or F : the thermal processing using a batch retort is a continuous process
f
What is the name of the machine that is u-shaped and used in the conventional thermal processing for canning
hydrostatic cooker and cooler
T or F : the hold time of the thermal processing takes into account only the D-value
False, it needs to take into account the come-up and come-down times.
Where are placed the thermocouples that measure the product heat
at the cold point
What factor influence the location of the cold point in food?
it depends on the type of heat transfer that is predominant in the food. For solids it is conduction and for liquids it is convection
Complete : for conduction in heat penetration studies, the cold point will be at ___ of the can
center
Complete : for convection in heat penetration studies, the cold point will be at ___ of the can
1/3 up from the bottom
T or F : heat tranfer characteristics can change during the thermal processing
true, example for gelatinization will slow down the rate of heat transfer.
What is the temperature of pasteurization of milk in the HTST ?
71C for 15 seconds then rapid cooling at 2C
What is the temperature for UHT in milk pasteurization?
over 100C for 1 second
What is the commonly used method for pasteurization of milk ?
HTST pasteurization with plate heat exchangers.
When was developed the UHT processing
1970
Since what year do we use the HTST pasteurization
1930
What are the three advantages of aseptic processes?
- continuous
- Very high and efficient heat transfer rates
- Not constrained by the container size and shape
What are commonly used to sterilize the packaging in the asceptic processing
UV light and hydrogen peroxide
What is the temperature and time of batch processing
62,5 for 30 minutes
How does heat kill the microorganisms?
by denaturing the proteins and inactivating their enzymes.
T or F : the asceptic processing is useful for heat sensitive products.
True, owing to HTST.
What is the temperature and time used for commercial sterility?
Depends on the product, but the time should result in a 12log reduction of the microbial load and that depends on the temperature.
