EX. 22 | Physical Methods of Control: Heat

Optimal Growth Ranges

Psychrophilie (0 to 20^oC)

Psychrotrophic (20 to 30^oC)

Mesophilie (25 to 40^oC)

Thermophilic (45 to 65^oC)

Hyperthermophilie (80^oC or higher)

Types of Heating

Dry Heat

Moist Heat

Dry Heat

Includes hot-air ovens, incineration (flaming inoculating instruments)

• Denatures enzymes, dehydrates microbes, and gets killed by oxidation effects

Moist Heat

Includes pasteurization, boiling, and autoclaving

Pasteurization

• Temperature is maintained at 63^oC for 30 minutes, or 72^oC for 15 seconds

• Kills pathogenic organisms that cause spoilage, but not ALL bacteria
  
  

Boiling

• 100^oC for 10 minutes will kill vegetative bacterial cells, but is not enough to kill endospores
  
  

Autoclaving

• Use of steam under pressure

• 15 psi at 121^oC for 16 minutes

• Kills all microbial life, including endospores

• Good method for sterilization

Effectiveness of Heat

Thermal Death Time (TDT)

• Length of time required to kill all bacteria in a liquid culture at a given temperature
  
  

Thermal Death Point (TDP)

• Temperature required to kill all bacteria in a liquid culture in 10 minutes
  
  

Decimal Reduction Time (DRT)

• Time in minutes in which 90% of a population of bacteria at a given temperature will be killed