Preservation Flashcards
What is thermal death time?
The time it takes at a given temperature to completely destroy all the microorganisms in a population
Destruction is logarithmic; theoretically impossible to completely destroy microorganisms.
What does D-value represent?
The time required to cause a one-log decrease, or 90% reduction, at a given temperature.
What is the D value for L.monocytogenes at 60°C?
1.6-16.7 minutes.
What factors influence heat resistance in microorganisms?
- Type of microorganism
- Incubation conditions during growth
- Conditions during heat treatment (temperature, age of culture, pH, water activity, food composition)
- Growth media and incubation conditions used in studies.
What are the three stages of heat treatment?
- Warming up
- Holding at maximum cooking temperature
- Cooling
At what temperature do most enzymes, microorganisms, and toxins get destroyed quickly?
Above 70-80°C.
What is sodium benzoate and its E number?
A widely used food preservative with an E number of E211.
What is the mechanism of action of sodium benzoate?
Absorption of benzoic acid into the cell, lowering intracellular pH inhibits microbial growth.
What is ALP and its significance in milk pasteurisation?
Alkaline Phosphatase is an enzyme used as an indicator of proper milk pasteurisation.
What is the classic test for ALP activity?
The Scharer Rapid Phosphatase Test.
What is the effect of heat on microorganisms?
Heat denatures proteins, destroys enzyme activity, and follows a logarithmic order of death.
What methods are included in food preservation?
- Heat treatment (cooking, pasteurisation, sterilisation, canning)
- Refrigeration and freezing
- Gas and vacuum packaging
- Drying/dehydration
- Irradiation
- Chemical additives (acids, salt, sugar, smoke, preservatives)
What are traditional methods of food preservation?
- Curing
- Pickling
- Sugaring
- Fermentation
What is specific heat?
The amount of heat needed to raise the temperature of 1 kg of a material by 1°C.
What are the three ways heat can be transferred into or out of food?
- Conduction
- Convection
- Radiation
What is the primary function of refrigeration?
To inhibit metabolic activity, microbial growth, and enzyme action.
What are the methods of milk pasteurisation?
- Low temperature – long time (LTLT) at 63°C for 30 min
- High temperature – short time (HTST) at 72°C for 15 sec
- Ultrahigh temperature (UHT) at 138°C for 2 sec
What is the effect of freezing on food quality?
- Slight reduction of nutrients
- Blanching may lead to vitamin loss
- Food texture deteriorates on thawing
What does modified atmosphere packaging (MAP) do?
Changes the gaseous atmosphere surrounding a food product for preservation.
What are the factors affecting the use of food preservatives?
- Concentration
- Presence of capsules/spores
- Anti-microbial spectrum
- Period of contact
- Temperature
- Number of microorganisms
- pH
- Presence of inactive substances
What is the definition of a preservative?
Any substance that inhibits, retards, or arrests the growth of microorganisms or deterioration of food.
What are the principles of canning?
- Pack food in an impervious container
- Kill all microbial flora
- Inactivate all enzymes present
What is commercial sterility in canned foods?
Processed so that any surviving microbes cannot grow.
What is the D value for C.botulinum at 110°C?
6.8-13 minutes.
