Food Microbiology Flashcards
Extrinsic factors affecting microbial growth?
Temperature
Relative humidity
Carbon dioxide or oxygen
Types and numbers of m.o in the food
Physical damage due to improper handling.
•insects, rodents, birds and domestic animals
Micro organisms.
Principles of food preservation
•thermal process?
Most bacteria are killed at 82-93•c
Spores are resistant
High acid foods require less heat
Pasteurization elimates only disease causing micro organisms in milk
121*c of wet heat for 15min is required to ensure sterility.
Pasteurization?
Kills pathogens.
Substantially reduces the number of spoilage micro organisms.
Shorter heating times are ideal as they result in improved flavor
Canning principles?
Food is heated in special containers(retorts).
•to 115*c 25 to 100 minutes.
• substantially reduces number of spoilage micro organisms.
•shorter heating times are ideal as they result in improved flavor.
Spoilage of canned food
Spoilage prior to canning
Under cooking
Entry of contaminated water into damaged cans during chilling.
Cold temperature
Food should not be frozen after thawing.
Freezing may kill some but not all micro organisms.
Growth at temperature below -10*c has been observed.
Low temperature
Psychrophiles will continue to grow slowly.
Refrigeration at 4*c retards but does not stop microbial growth
M.O can still cause spoilage with extended refrigeration
Drying
Dehydration of food also dehydrates the micro organisms.
M.O contains approximately 80% of moisture
Sun drying is limited to some foods
Freeze drying (lyophilization) is the most effective method
Sugar or salt
One of the oldest preservation methods
Addition increases the affinity of the food for water
Decreases water activity in the food
Removes water from the micro organism through osmosis
Smoke
Contains formaldehyde and other preservatives
Heat during smoking also helps reduce microbial populations and dries the food.
Atmosphere
Excludes air control of aerobic micro organisms.
Provides air for control of anaerobic micro organisms.
Intrinsic factors affecting microbial growth.
•pH Enzymatic reactions Moisture content Water activity Oxidation-reduction potential Physical structure of the food Chemical reactions- available nutrients Presence of anti microbial agents.
