What Do You Understand by Thermal Preservation of Foods Flashcards

- controlled processes that are performed commercially.
1) Blanching
2) Pasteurization
3) Commercial sterilization

Mild-intensity heat process
- exposing fruit/vegetables to boiling wateror steam fora short period of time.

Preservation principle:
- inactivate endegenous (growing/developing from within) enzymes
- drives off oxygen and other gases (minimize pressure build-up)

Moderate-intensity heat process
- temperature below boiling point of water 60-80 degrees celcius
a) 30-40 mins at 60 degrees --> low temp, long time=LTLT
b) 15 secs at 72 degrees --> high temp, short time=HTST
(flash past)
- Conducted PRIOR to packaging

Preservation Principle (2 objectives):
1) Low-acid foods (milk, eggs)
- to destroy pathogenic (disease-causing) bacteria&viruses
- to inactivate enzymes

2) Acid foods (beer, wine, fruit juices)
- to extend product shelf- life
*destroy spoilage-causing MOs & enzymes
*acid foods not a source of pathogens
pasteurized vs unpasteurized juices

Yes, many spoilage-causing MOs can survive pasteurization especially in low acid foods.
- combined with other forms of preservation: ex. refrigeration - "durable life date" at <_ 4C.

- psychrotrophic bacteria
- putrefactive spoilage (protein)
- liplolytic spoilage (lipid)

cant surivive - lactic acid bacteria! usually leads to souring of raw milk

- foods that will be consumed within a short period of time after processing.
- storage life partially extended by combinationof pasteurization & refrigerated process
ex. milk, some cured meat products, smoke salmon

High-intensity heat process
- also aka canning if used in canned product.
- requires a minimum of 121 C moist heat for 15 mins

- Destroys spoilage-causing & disease causing MOs.
- Free form viable (germinating) forms of MOs (including spores)

Survive:
-Small numer of heat-resistnat spores but doesnt multiply (germinate) in the food product even if held at room temperature.


- Ensures that the spores of Clostridium btulinum are destroyed = botulinum cook.

BOTULISM
- in latin botulus = sausage
- bacteria present in soil, water, air
- strict anaerobe (absences of O2)
- grows well in low acid foods
- produces a potent toxin (neurotoxin)
a) affects central nervous system
b) vertigo (dizziness), blurred vision, difficulty breathing & swallowing, slurred speech
c) worst cases: death from respiratory collapse or cardiac arrest

Conducted once the food is packaged in suitable containers.
- containers must withstand the high temp & pressures used
- containers must be hermetically sealed (impermeable to transmission of gases, liquids, and microorganisms

CS products have a shelf life of 2 years or more (ex. canned foods)

1) UHT Processing (Ultra High Temperature)
- injection of hot steam under pressure (140-150C) for a short time (4-6 sec) , followed by immediate cooling

2) Aseptic packaging
- UHT food is aseptically (free of microorganisms that cause disease) placed into pre-sterilized containers and sealed in an aseptic environment
ex. shelf-stable milk, juice

- shelf life >_ 6 months without refrigeration!
- some UHT treated foods are not necessarily aseptically packaged meaning not commercially sterile!
*longer shelf life at refrigeration temperatures
*not shelf stable (at room temp)

Longer storage times at room temperatures in sealed containers.
-used for canned goods, UHT/aseptic pack products

important factors that must be taken into consideration
- appropriate heat treatment
- thermal death curves (TDC), TDRC and TDTC
- margin of safety
- heat transfer mechanism

1) sufficient heat
- destroy microorganisms & food enzymes
- also affect other properties of food
2) mildest HT that guarantees freedom from pathogens and toxins
- at the same time, produce desired storage life.

Clarification, homogenization, pasteurization

Microorganisms are not killed instantaneously. takes time.
- microbial death = logarithmic order of death
- under constant thermal conditions the same % of microbial population will be destroyed in a given time interval (regardless of the surviving population)