Methods of food preservation M Cold storage M Heat processing M Reduced aw M Acidification M Atmosphere modification M Addition of chemical preservatives M Ionizing radiations
Cold Storage M Freezing M Refrigeration
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Freezing M Needs previous conditioning M Freezing is applied to previously packaged foods
M Meats, poultry, seafood, eggs etc. – Trimming – Packaging
Freezing M Blanching M Enzyme inactivation M Fixing green color in some vegetables M Easing packaging of leafy vegetables (by wilting) M Displacing of air from plant tissues M Reduction of microbial counts
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Freezing M Fast freezing – Lower temperature to -20°C within 30 min – Blast freezing or immersion
M Slow freezing M Lower temperature to -20╖C within 3-72 h M Home freezers
Freezing M Effects of freezing on microorganisms M Sudden mortality immediately on freezing M Continued mortality rate decreases gradually during storage M The lower the temperature the lower the bacterial decline
Refrigeration M The lower the temperature the lower the growth rate M How can psychrotrophs grow at refrigeration temperatures?
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Psychrotrophs and psychrophiles M Greater content of unsaturated fatty acids M Slower metabolic rate M Better membrane transport – Still active at low temperatures
M Production of larger cells M M M M
– Additional RNA
More efficient flagella synthesis Favored by aeration Greater heat sensitivity Usually do not grow above 35°C
– Inactivation of respiratory enzymes – Leakage of intracellular constituents
Heat processing M Pasteurization M Sterilization
Pasteurization Types of milk pasteurization
Acronym
Treatment
Low temperature long time
LTLT
63°C/30 min
High temperature short time
HTST
72°C/15 s
Ultrahigh temperature
UHT
90°C/0.5 s 94°C/0.1 s 100°C/0.01 s
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Pasteurization Milk pasteurization M Originally designed to target Mycobacterium tuberculosis M Coxiella burnetti is currently the target organism
Pasteurization M Thermoduric organisms – Organisms capable of surviving pasteurization – Examples: lactobacilli, micrococci, streptococci, lactococci – Pathogens are not thermoduric
Factors affecting heat resistance of microorganisms M Water M Fat M Salts
– Salts that reduce aw (Na+, K+) more protective than those that increase aw Ca+2, Mg+2)
M Carbohydrates M pH
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Factors affecting heat resistance of microorganisms (cont.) M Proteins M Numbers of microorganisms M Age or microorganisms
– Old cells (stationary phase) more resistant that younger cells (log phase)
M Growth temperature M Inhibitory compounds M Time and temperature M Ultrasonic effect
Canning M Processing of food products in hermetically sealed containers – Metal – Glass
M Canned products are commercially sterile
Spoilage organisms associated with canned products Mesophilic M Putrefactive anaerobes – Clostridium spp.
M Butyric anaerobes – C. butyricum
M Aciduric flat sour
– Paenibacillus polymyxa
M Lactobacilli M Yeasts M Molds
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Spoilage organisms associated with canned products (cont.) Thermophilic M Anaerobic sulfide producers – Desulfotomaculum nigrificans
M Flat-sour spores M Geobacillus stearothermophilus, Bacillus coagulans M Anaerobic non-sulfide producers – Thermoanaerobacterium thermosaccharolyticum
Canning pH category
Examples of foods Spoilage
Low acid > 4.6
Meats, seafood, milk, some vegetables
M Thermophilic flatsour group M Sulfide spoilers M Gaseous spoilers M Mesophilic spoilers – Putrefactive anaerobes
