Heat and Sterilization Methods

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Questions and Answers

What is the primary purpose of pasteurization?

To sterilize milk completely.

To improve the keeping quality of milk while maintaining its nutritive value. (correct)

To kill all microorganisms in milk.

To convert milk to yogurt.

What temperature and duration are required for sterilizing the cholera vaccine?

56°C for one hour (correct)

62°C for 30 minutes

55°C for 15 minutes

72°C for 15 seconds

What is latent heat in the context of water heating?

It represents the heat lost when water changes from vapor to liquid.

It is the temperature at which water boils.

It is the heat absorbed by water during the phase change from liquid to vapor. (correct)

It refers to the heat required to raise the temperature of water.

Which method combines heat with a bactericide for sterilization?

Sterilization by heating with bactericide Signup and view all the answers

Why is the method of heating with bactericides not used for certain injections?

The bactericide may cause toxicity in larger volumes. Signup and view all the answers

What is the key advantage of using an autoclave for sterilization?

It uses hotter steam than boiling water. Signup and view all the answers

What is the main disadvantage of using superheated steam for sterilization?

It acts only as a heat source and lacks moisture. Signup and view all the answers

What is the holding process in pasteurization?

Heating at 62°C for 30 minutes followed by cooling. Signup and view all the answers

What type of bacteria did Louis Pasteur originally target with his pasteurization process?

Non-spore forming bacteria Signup and view all the answers

Why is the condensation of saturated steam beneficial during sterilization?

It releases latent heat, quickly raising temperatures. Signup and view all the answers

What is the primary use of formaldehyde in sterilization?

Fumigation of contaminated rooms Signup and view all the answers

At what temperature does water boil at one atmospheric gauge pressure?

121°C Signup and view all the answers

What characteristic of saturated steam allows it to sterilize effectively?

Ability to penetrate objects and provide uniform temperature. Signup and view all the answers

What is the primary use of an autoclave?

To sterilize items under controlled temperature and pressure. Signup and view all the answers

Which of the following statements is true regarding the temperature-pressure relationship in sterilization?

Temperature is directly proportional to the pressure during boiling. Signup and view all the answers

What must be done to sterilized articles after using ethylene oxide?

Keep them in a well-ventilated area to remove ethylene oxide Signup and view all the answers

What is the capacity range of the gas autoclave chamber?

100-300 liters Signup and view all the answers

What is a key feature of the gas autoclave design?

Contains a vacuum pump for air evacuation Signup and view all the answers

Which method can formaldehyde be used for in sterilization?

Low temperature steam and formaldehyde (LTSF) Signup and view all the answers

What happens when water is finished in the sterilization process while heating continues?

The saturated steam converts into dry steam. Signup and view all the answers

What is the main disadvantage of using autoclaving for sterilizing glass?

Repeated autoclaving causes damage. Signup and view all the answers

Which factor plays no role in the killing process during moist heat sterilization?

Pressure. Signup and view all the answers

Which type of autoclave is heated electrically and used for small-scale sterilization?

Portable autoclave Signup and view all the answers

Why is air removed from the autoclave during the sterilization process?

To ensure complete penetration of steam. Signup and view all the answers

At what minimum temperature are dressing sterilizers typically operated?

134°C Signup and view all the answers

What is a primary advantage of jacketed autoclaves?

They allow for rapid operation as steam is stored. Signup and view all the answers

What type of sterilizer is specifically designed for bottled fluids?

Bottled fluids sterilizer Signup and view all the answers

How does the presence of air affect sterilization temperature in pressure controlled autoclaves?

It lowers the effective temperature due to specific heat differences. Signup and view all the answers

What is a common misconception about sterilizing small sealed containers, such as ampoules, in an autoclave?

They can be fully filled with liquid. Signup and view all the answers

What is the primary mode of action of ethylene oxide in sterilization?

Alkylation of specific functional groups in proteins and nucleic acids Signup and view all the answers

Why is ethylene oxide not suitable for sterilizing items in sealed glass or metal containers?

It has insufficient penetration capability Signup and view all the answers

What is a significant disadvantage of ethylene oxide sterilization?

It has mutagenic and carcinogenic properties Signup and view all the answers

At what relative humidity does the activity of ethylene oxide decrease due to its alkylating properties?

Above 60% Signup and view all the answers

What is the appropriate exposure time for items being sterilized with ethylene oxide?

1 to 4 hours Signup and view all the answers

Which of the following items are suitable for sterilization using ethylene oxide?

Surgical dressings and sutures Signup and view all the answers

Which of the following gases is a component in the ethylene oxide sterilization mixture to enhance its properties?

Carbon dioxide Signup and view all the answers

What are the safety concerns associated with the use of ethylene oxide?

It is flammable and potentially explosive with air Signup and view all the answers

Study Notes

Sensible and Latent Heat

1 gram of water needs 100 calories to raise its temperature from 1°C to 100°C. This heat is considered sensible heat.
1 gram of water needs 560 calories to convert it from water at 100°C to steam at 100°C. This heat is called latent heat.

Moist Heat Sterilization Methods

At Normal Pressure (At or Below 100°C)
- Pasteurization: Not used for sterilization, but for preservation.
  - Introduced by Louis Pasteur to kill non-spore forming bacteria like Acetobacter and Lactobacillus.
  - Used to kill pathogens in milk, like T.B., Brucella, Salmonella, and poliovirus.
  - Improves milk's keeping quality while retaining its nutritional value.
  - Two methods:
    - Holding process: 62°C for 30 minutes, followed by cooling to 7°C.
    - Flash process: Heated at 72°C for 15 seconds, 82°C for a few seconds, and then rapidly cooled to 4°C.
- Vaccine Sterilization:
  - Uses heat to kill microorganisms without affecting their antigenicity.
  - Cholera vaccine is sterilized at 56°C for one hour.
  - Plague vaccine is sterilized at 55°C for 15 minutes.
  - Staphylococcus autogenous vaccine is sterilized at 62°C for 15 minutes.
- Sterilization by Heating with Bactericides:
  - Involves heating at 100°C for 30 minutes with a bactericide.
  - Bactericides should be non-toxic, non-volatile, stable, and compatible with other ingredients.
  - Examples include phenyl mercuric nitrate, benzalkonium chloride, and chlorocresol.
  - This is a combination of chemical and heat sterilization.
  - Disadvantages:
    - Not used for injections exceeding 15 ml due to potential toxicity.
    - Not used for oily injections as oils reduce the effectiveness of water-soluble bactericides.
    - The bactericide remains in the final preparation.
At High Pressure (Above 100°C)
- To achieve temperatures above 100°C, water must boil under pressure.
- Temperature is directly proportional to pressure.
- Moist heat sterilization typically uses steam at temperatures between 115°C and 134°C.
- Pressure only raises the boiling point of water, not involved in the killing process.
- Autoclave:
  - A large pressure cooker with controls for temperature, pressure, air, and cooling.
  - Used for large-scale pharmaceutical and hospital settings for sterilizing thermostable aqueous injections, surgical dressings, and microbiological media.
  - Not suitable for oils, powders, or glass as repeated autoclaving can damage them.
  - Used for emergency glass sterilization.
  - Empty closed ampoules cannot be sterilized in an autoclave as water won't reach the inner surface.
  - Main Design Features:
    - A double-walled chamber, usually made of metal, with the outer wall having a jacket for controlled heating.
    - Includes a pressure gauge, temperature gauge, and a safety valve.
  - Types of Autoclaves:
    - Portable Autoclave (Bench Autoclave)
      - Steam is generated inside the autoclave, resulting in wet steam.
      - Made of pressure-resistant metal or stainless steel, either vertical or horizontal.
      - May be double-walled with a steel jacket.
      - Heated electrically.
      - Used for small-scale sterilization in laboratories and for sterilizing instruments and utensils.
    - Stationary Autoclave (Large Sterilizer)
      - Larger, horizontal vessel with a complex design.
      - Steam is supplied from a separate boiler as dry saturated steam.
      - Usually surrounded by a steam jacket.
      - Used for routine hospital or industrial sterilization.
    - Types of Large Sterilizers:
      - Dressings (Porous Loads) Sterilizers:
        
        Operated at a minimum temperature of 134°C.
        
        Equipped with a vacuum pump to remove air at the beginning and steam at the end of the process, ensuring a dry load.
      - Bottled Fluids Sterilizers:
        
        Generally operated at 121°C.
        
        Have a device for spraying cold water to cool the load, or filtered compressed air.
        
        Small sealed containers, like ampoules, shouldn't be completely filled, to allow steam to form without cracking.
        
        Advantages of Jacketed Autoclaves:
        
        Rapid operation due to stored steam in the jacket.
        
        Economically efficient as steam is trapped in the jacket.
        
        Load emerges dry because the inner surface remains warm.
  - Why Air is Removed from the Autoclave:
    - Reduces steam penetration, especially in dressings.
    - Causes superheating in stationary autoclaves.
    - Increases risk of explosion in temperature-controlled autoclaves.
    - The temperature of the air-steam mixture may be lower than expected, hindering sterilization.
    - Requires more heat to reach the desired temperature, making it less economical.

Cold Sterilization

Gaseous Sterilization
- Uses specific alkylating agents like ethylene oxide, b-propiolactone, propylene oxide, and formaldehyde for broad-spectrum biocidal and sporicidal action.
- Ethylene oxide is an alternative to radiation sterilization for disposable medical devices.
- Does not offer the same sterility assurance as heat methods and is generally used for thermolabile items.
- Ethylene oxide and formaldehyde are thought to work by alkylating proteins and nucleic acids.
- Suitable for: Plastics, antibiotics, hormones, reusable medical instruments, surgical dressings and sutures, surface sterilization of powders.
- Not Suitable for: Substances that react with ethylene oxide (like serum, vaccines, and aqueous solutions), many oily preparations, preparations in sealed glass or metal containers.
- Properties & Disadvantages of Ethylene Oxide:
  - Gas at normal atmospheric pressure with a boiling point of 10.5°C.
  - Flammable and explosive when mixed with air in concentrations exceeding 3.5% v/v.
  - Often mixed with CO2 (carboxide) or Freon (cryoxide) due to its toxicity and flammability.
  - Toxic like ammonia.
  - Mutagenic and carcinogenic.
  - Slow action (exposure time: 1-4 hours).
- Factors Affecting the Efficacy of Ethylene Oxide:
  - Concentration: 800-1200 mg/liter of the sterilizer volume.
  - Temperature: 45-63°C.
  - Relative Humidity: 30-60% (activity decreases below 30% due to reduced alkylation and above 60% due to inactive ethylene glycol formation).
- Penetration:
  - Ethylene oxide does not penetrate glass, metals, and crystals.
  - It can be used for surface sterilization of plastics, and penetrates fabrics and paper.
- Sterilizer Design and Operation (Gas Autoclave):
  - Leak-proof and explosion-proof steel chamber with a capacity of 100-300 liters.
  - Surrounded by a hot water jacket to control temperature.
  - Equipped with a vacuum pump to remove air and gas mixture.
  - A source of steam for humidification is required.
  - Sterilized articles must be ventilated for a period to remove adsorbed ethylene oxide due to its skin corrosiveness.
- Formaldehyde Sterilization:
  - Uses:
    - Fumigation of contaminated rooms and spaces.
    - Sterilization of reusable medical devices, like endoscopes, using low temperature steam and formaldehyde (LTSF).

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Description

This quiz explores the concepts of sensible and latent heat, detailing the energy requirements for heating water and its phase change. Additionally, it covers various moist heat sterilization methods, including pasteurization and vaccine sterilization, highlighting their significance in food safety and microbiology.