Microbiology Chapter 5 – Microbial growth control
Microbial growth control;
We wash fresh produce to remove attached organisms and we inhibit microbial
growth on body surfaces by washing.
Microbial growth; exponential increase in biomass; a straight ascending line
Microbial elimination; exponential decrease in biomass; a straight descending line
Physical
Inhibiting microbial growth
• Decontamination; treatment of an object or surface to make it safe to handle
(wiping off food utensils to remove food fragments)
• Disinfection; process that directly targets pathogens although it may not
eliminate all microorganisms (requires agents, disinfectants, to kill
microorganisms or inhibit their growth)
Heat
Decrease the biomass, how higher the temperature how steeper the line.
Type of temperature is also important, moist heat has better power than
dry heat. Moist heat inhibits growth or kill cells more quickly.
Decimal reduction time (D); time required to reduce the number of
bacteria from 100% to 10%.
How many decimal reduction times are needed to achieve a 1% reduction is 2
Thermal death time; time it takes to kill all cells at a given temperature
Sterilization; 121 degrees, 15 min
Pasteurization; 71 degrees, 15 sec
• Advantage; taste changes less
• Drawback; not sterile; cells, bacterial spores survive. The bacterial spores are
very heat-resistant because of -low water content -Ca2+-dipicolinate
accumulation -special spore proteins.
• Originally used for wine and beer
Autoclave; is sealed heating device that uses steam
under pressure to kill microorganisms. Killing of
heat-resistant endospores require heating at
temperature above 100 degrees.
Autoclave places the steam which yield temperature
to 121 degrees.
Watch out; the temperature kills the microorganisms
NOT the steam.
Radiation
Decrease the biomass.
Microwaves; denaturation
UV; DNA fracture, DNA is destroyed and bacterial will die
Microbial growth control;
We wash fresh produce to remove attached organisms and we inhibit microbial
growth on body surfaces by washing.
Microbial growth; exponential increase in biomass; a straight ascending line
Microbial elimination; exponential decrease in biomass; a straight descending line
Physical
Inhibiting microbial growth
• Decontamination; treatment of an object or surface to make it safe to handle
(wiping off food utensils to remove food fragments)
• Disinfection; process that directly targets pathogens although it may not
eliminate all microorganisms (requires agents, disinfectants, to kill
microorganisms or inhibit their growth)
Heat
Decrease the biomass, how higher the temperature how steeper the line.
Type of temperature is also important, moist heat has better power than
dry heat. Moist heat inhibits growth or kill cells more quickly.
Decimal reduction time (D); time required to reduce the number of
bacteria from 100% to 10%.
How many decimal reduction times are needed to achieve a 1% reduction is 2
Thermal death time; time it takes to kill all cells at a given temperature
Sterilization; 121 degrees, 15 min
Pasteurization; 71 degrees, 15 sec
• Advantage; taste changes less
• Drawback; not sterile; cells, bacterial spores survive. The bacterial spores are
very heat-resistant because of -low water content -Ca2+-dipicolinate
accumulation -special spore proteins.
• Originally used for wine and beer
Autoclave; is sealed heating device that uses steam
under pressure to kill microorganisms. Killing of
heat-resistant endospores require heating at
temperature above 100 degrees.
Autoclave places the steam which yield temperature
to 121 degrees.
Watch out; the temperature kills the microorganisms
NOT the steam.
Radiation
Decrease the biomass.
Microwaves; denaturation
UV; DNA fracture, DNA is destroyed and bacterial will die
