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Asked Feb 7, 2020
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Identify and describe the 4 wet-heat methods that are used to control microbial growth.

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Expert Answer

Step 1
  • The different methods used for controlling the growth of microbes by moist heat are boiling, autoclaving, pasteurization, and Tyndallization.
  • Boiling is the process of heating a liquid substance at 1000 C for 10 minutes. It causes the denaturation of bacterial proteins and disrupts their plasma membranes. One of the disadvantages of this method is the inability to kill bacterial endospores. It is generally used to disinfect drinking water.
Step 2

Autoclaving is a method of steam sterilization that uses steam under high pressure to kill microbial cells and spores. It is carried out at a temperature of 1210 C for 15-20 minutes at 15 psi (pounds per square inch) pressure. However, the time for autoclaving increases if the volume of the solution is high as it will take time for the center of the solution to reach the desired temperature. The steam produced by boiling water is introduced into the autoclave chamber and the air already present is removed. The spores of bacterium Geobacillus stearothermophilus are used as an indicator to check if sterilization has taken place properly. A strip covered with spores of these bacterium and a sterile ampule is placed in the autoclave. After completion of the process, the ampule is broken and incubated in culture to check for growth. If there is no growth, it is concluded that sterilization has effectively killed all the vegetative cells and spores.

Step 3

Pasteurization is a moist heat method that involves the controlled heating of a substance. It is performed at a temperature below the boiling temperature. This method is used to prevent spoiling of milk, juice, beer, wine, and other edible liquids. It preserves the quality of food while killing pathogenic and spoilage causing microbes. It is of two t...

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