– kills endospores
• Pasteurization
– kills certain microorganisms
– Bacteria
Fungi
Spores
5-10 min. 60-70oC
5-10 min.
5-10 min.
50-60oC 70-80oC
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– minimal time – kill all microorganisms (sterilize)
• liquid suspension
– at given temperature
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Conditions that Affect Antimicrobial Activity
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Decimal Reduction Time
• Example: 1,000,000 (106) • 1 minute = 90% killed • 2 minutes = 100,000 (90%) • 3 minutes = 10,000 • 4 minutes = 1,000 • 5 minutes = 100 • 6 minutes = 1 cell
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Microbial Death Rate
• Decimal reduction time
– D-value – time required to kill
90% of cells
• Heat treatments
– temperature – type of microorganism – physiological state – other substances
Pasteurization
• Involves heating to temperatures below boiling for certain time periods (63-66oC for 30 minutes)
– Does not kill all microbes, but only those causing disease
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Physical Controls
• Heat
– Moist
• boiling
– kills most vegetative cells, not sterile
• autoclave
– steam under pressure: 15 lbs./in2 at 121oC for 15 min.
Chapter 9 Controlling Microorganisms
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ቤተ መጻሕፍቲ ባይዱ
Controlling Microbial Growth
• Antimicrobial
– Kills or prevent growth of microbes
• Disinfection
– reduces number of pathogens
– pose no danger of disease
• Decontamination
– renders contaminated surface safe to handle
• Antisepsis
– kills microorganisms on living tissue
• Temperature
– Higher Temp. greater number killed
• Substrate
– Affect the efficiency of agent
• Microbial characteristics
– Susceptibility to different agents
• Population density
– Larger number the more time
• Concentration
– Increase in concentration decreases in time
• Time exposure
– Increase exposure increases the number of killed
• Microbiocidal
– Kills all microbes
• Sterilant
– Kills vegetative & endospores
• Microbiostatic
– Only inhibits the growth of microbes
• Sterilization
– destroy all microbial life
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Sterilization
• Thermal death point
– lowest temperature – kill all microorganisms in broth – 10 minutes
• Thermal death time
– Reduces the numbers of microbes that cause food spoilage
• New method of Pasteurization
– Short term flash 71.6oC for15 seconds
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© 2004 Wadsworth – Thomson Learning
Mechanisms of Microbial Agents
• MODE OF ACTION • Interferes with cellular components
– Cell membrane – Cell wall – Ribosomes – Genetic material (DNA) – Enzymes – Cytosol