Chatper 7- The Control of Microbial Growth Flashcards
Sterilization
destroys all forms of life
commercial sterilization
sufficient heat treatment to kill C. botulinum endospores in canned food
disinfection
treatment used to kill bacteria on objects
antisepsis
treatment to kill bacteria on tissue
degerming
removing microbes from a limited area
sanitization
removing microbial counts on eating utensils
sepsis
presence of a toxin or pathogen in blood/tissue
asepsis
the absence of contamination by unwanted bacteria
factors that influence effectiveness of microbial control agents
# of microbes presence of organic matter temperature (heat is more effective in acidic conditions, heat is less effective against microbes in the presence of fats and proteins) time exposure microbial characteristics
actions of microbial control agents
damage to the cell membrane (susceptible due to lipid/protein components)
damage to proteins and nucleic acids
Methods of control
Physical: Moist heat (denatures proteins), pasteurization, dry heat (coagulates proteins, dries cells, oxidizes), filtration, cold, high pressure, desiccation, radiation. And chemical
Thermal Death Point
lowest temperature where all microbes in a liquid will be killed in 10 minutes.
thermal death time
length of time required to kill all bacteria in a liquid culture at a given temperature
decimal reduction time
length of time required to kill 90% of a bacterial population at a given temperature
pasteurization
eliminates pathogens/reduces spoilage organisms
equivalent treatments 63 C for 30 min, HTST(72C for 15 sec)
Dry heat sterilization
examples are hot-air sterilization, direct flaming to a red glow, and incineration.
filtration
- High-efficiency particulate Air (HEPA) filters remove microbes larger than 0.3 microns
- membrane filters remove microbes more than 0.22 microns or even 0.01 microns
Low temperatures on microbial growth
refrigeration (0-7C) is bacteriostatic as even psychrotrophs will still grow slowly and eventually alter food.
deep-freezing usually renders them dormant without killing them. However, ice crystals can be formed which will disrupt structure( slow freezing is more harmful than rapid)
high pressure on microbial growth
Very high pressure for 3-5 min applied to a liquid suspension is instantly transferred equally through a food package. This can cause denaturation of proteins, phospholipid gelation, and irreversible damage resulting in loss of membrane. This method can be used for food because is doesn’t use heat (while it inactivates most vegetative cells, it doesn’t work on endospores)
Desiccation
metabolism is prevented but cells can remain viable.
Resistance: endospore>viruses>vegetative cells
Osmotic pressure on microbial growth
high salt/sugar concentrations create hypertonic conditions which will cause the cell to crenate. However, yeast/molds are much better at growing on low moisture/high osmolarity foods).
Radiation
Ionizing(X-rays, gamma, high energy electron beams): ionize H2O to release hydroxyl radicals that will react with cell components.
Nonionizing (UV, 260nm): causes thymine dimers
Microwaves kill by heat
Phenol
significant bacteriocidal effects above 1%, but rarely used because it irritates skin; it works by injuring the cell membrane.
Phenolics
derivatives of phenol that were made to reduce irritation and increase antimicrobial effects (active in presence of organics, stable, persist long after application)
