Thermal Processing Flashcards
What are the 3 basic mechanisms by which food is transferred?
conduction, convection, and radiation
What is conduction?
Heat and energy is transferred from one molecule to an adjacent molecule (through containers without a gross change in relative positions of the molecules. This is done with solid foods.
What is convection?
The transfer of heat by groups of molecule that move as a result of differences in density or as a result of agitation. This is done with fluid foods.
What is radiation?
Heat transfer by electromagnetic waves emitted by hot objects. This is done through infrared, microwave, and dielectric heating.
What are 4 types of thermal processes?
- Cooking
- Blanching
- Pasteurization
- Sterilization
What is the objective of cooking foods?
To increase palatability (mainly), destruct some spoilage and pathogenic microorganisms, and inactivate deteriorative enzymes. It also inactivates some anti-nutritional factors and improves digestibility.
What are some undesirable changes to cooking?
Loss of nutrients and decline of sensory quality
How are nutrients lost during cooking?
- Lysine bioavaibilty goes down
- Heat sensitive vitamins are killed (A & D)
- Water soluble vitamins goes down (B vitamins)
What is the objective of blanching?
Inactivate deteriorative enzymes and kill spoilage bacteria.
What are two types of blanching?
- Atmospheric steam/boiling water
2. Pressurized steam/ hot gas
Why is blanching done before freezing or canning?
To prevent damage
Describe a typical industrial blanching machine.
A mesh convayer carries food through steam atm in a closed tunnel
When is blanching done?
Before freezing and canning and before drying.
Why do you blanch before freezing and canning?
To remove gases and clean tissues.
Why do you blanch before drying?
To extend shelf life and destroy enzymes.
What is Lipoxygenase?
development of off-flavour in soybeans and grozen veggies, colour change in flour, loss of vitamin a and fatty acids
What is polyphenol oxidase?
Responsible for enzymatic browing
What is pectinase
Responsible for softening of plant tissue by breaking down pectin
What is the “hot break process”
The loss of viscosity in tomato juice if not treated immediatly
What is used as an indicator of the severity of nutrient loss during blanching?
The loss of absorbic acid because it is thermally labile and subject to enzymatic breakdown.
What type of blanching effects nutrient loss the most and the least?
Most: water blanching with cold water
Least: Steam blanching with cold air
What is pasteurization?
A heat treatment that kills part of the microbial population that is present within food whilst only minimally changing sensory or nutritive value
What is the primary object of pasteurized milk?
To kill pathogenic microorganisms and extend shelf life.
What pathogens are targeted in milk through pasteurization? (2)
Mycobacterium tuberculosis and coxiella burnetti
What is LTH pasteurization?
Set at a low temperature for a long time.
What is HTST pasteurization?
Set at a high temperature for a short time.
Compare LTH and HTST.
Basically the same but LTH kills more nutritional and sensory properties.
Why shouldnt you drink raw milk?
Because many pathogens are present in milk.
What is batch process pasteurization and when is it used?
Milk is heated in a holding tank for a specific period of time, used in small scale operations.
What is continuous process and what equipment is used?
Milk flows though a heat exchanger while the desired time and temperature is obtained. This is done with a plate heat exchanger (PHE) providing a high production rate and not milk overheating.
What other foods are pasteurized?
Beer, juice, eggs
What is sterilization?
The process used in canning, retorting and UGT (ultra high temp) processing food. Done at extremely high temperatures.
What are 4 types of microorganism destruction processes?
- Sanitation
- Pasteurization
- Commercial sterilization
- Sterilization
What does sanitation do?
REduces pathogens to a safe level (food processing plants)
What does pasteurization do?
Destroys all vegetative pathogens and many spoilage organisms (ready-to-eat)
What does commercial sterilization do?
Destroys all pathogens and all spoilage organisms that can grow under normal storage conditions (canned food)
What does sterilization do and how is it done?
No living organisms are present and it is done through autoclaving.
Why isn’t commercial sterilization true sterility?
Because some nonpathogenic spore forming bacteria may eventually grow under optimum conditions.
How is severity of thermal process required for killed bacteria determines?
The acidity of the food where low acid foods need more severe treatment
Why must a severe thermal process be used on low acid foods?
Becuase Blostridium botulinum will grow and produce a toxin at a pH of 4.6 or greater
When canning foods mid-acidic foods what is the primary target of thermal processing? How are they killed?
Faculative anaerobes. Boiling water at atm pressure.
How are high acid foods processed?
Thorugh a milder process because anaerobic bacteria wont grow. May “hot fill” containers at ~90degrees creating a slight vacuum.
Waht is UHT sterilization?
Ultra high temperature (140 for 2s).
How are UHT products packaged?
aseptically
What are some factors that influence the severity of thermal processes?
- Nature and heat resistance of microbes
- Initial microbial load
- Nature of food
- Heath transfer of container
- Heat transfer of food
- Condition of storage
- Canning equipment
Heat transfer during the sterilization of cans can retort via…
Conduction and convection
What is vital when heating cans?
Making sure that the mid point/coldest point reaches the desired temperature and times
What is thermal conductivity?
The measure of how fast a solid material can be heated
What is specific heat capacity?
Amount of energy required to raise the temperature of a unit mass of a substance by 1 degree.
If you heat a food containing oil and water which part of the food will be hotter?
The oil because its heat capacity is lower.
If the survival rate of microorganisms is plotted logarithmically vs. time what is observed?
A linear decrease. Logarithm of survival is proportional to time at a given temp.
The more time needed to decrease the microbial population at a given temp the ______ heat resistance is.
More
what is the D value?
The number of minutes required at a particular temperature to destroy 90% of microorganisms in a population. Or to decrease the population by 1 log cycle.
If it takes 2 minutes at a given temp to decrease the number from 1000 to 100 what is the d value?
2 minutes because it goes down by 1 log reduction and 2x1=2.
If it takes 2 minutes at a given temp to decrease the number from 10^4 to 10^0 what is the d value?
8 minutes (2x4=8)
If an organism takes a long time to kill what does that say about its heat resistance?
It is very heat resistant
How do we determine how long to heat a product to destroy a microorganisms?
multiply D value by 12.
What is the Z value?
The temperature needed to cause 1 log reduction in D value.
If the Z value for a particular sustem is 15 what does that say about the D value?
That the D value will reduce by 1log when the temperature increases by 15 degrees.
What is the F value?
The number of minutes required to kill a known population of a specific microorganism in a given food under specific conditions.
What factors affect D value before processing?
Type of microorganism, growth temperature, medium, and pahse
What factors affect D value during processing?
Type of food, pH, water activity, salt concentration, microorganism concentration, rate of heating
What factors affect D value after processing?
Recovery medium, temperature, presence of O2, background microflora
How can nutrient loss be characterized through thermal destruction?
With D and Z value.
Are nutrients or bacteria spores more heat resistant?
Nutrients
What type of thermal processing can retain the most nutrients?
HTST
What is batch processing?
A batch is heated, then unloaded and reloaded.
What is continuous processing?
Product moves through a conveyor belt or flow through pipes (more efficient)
What is indirect heating?
There is a barrier between the heating medium and the product.
What is direct heating?
There is contact between the heating medium and the product.
How many calories would it take to heat 1 gram of ice at 0degrees to steam at 100 degrees.
ice to water= 80 cal
water to water= 100 cal
water to steam= 540 cal
Total=720cal
