Yingtai: Characteristics of Different High-Temperature Sterilization Methods
High-temperature sterilization is a core method for killing microorganisms and is primarily divided into two categories: dry heat sterilization and moist heat sterilization.
I. Dry Heat Sterilization
1. Core Principle
Utilizes high-temperature dry air (without moisture) to destroy microbial structures through oxidation, inactivating enzymes and nucleic acids. Requires prolonged exposure to high temperatures.
2. Main Methods and Characteristics
- Flame Incineration
- Principle: Directly burns items until carbonized.
- Applications: Metal tools resistant to burning, such as inoculation loops and forceps.
- Drawbacks: Highly destructive; only suitable for items with no economic value.
- Dry Hot Air Sterilization
- Temperature and Time:
- 135-140°C for 3-5 hours
- 160-170°C for 2-4 hours (commonly used)
- 180-200°C for 0.5-1 hour (rapid sterilization)
- Applications: Glassware (e.g., syringes, test tubes), metal instruments, oily substances (e.g., ointments), and powdered medicines.
- Advantages: No moisture residue, preventing items from becoming damp.
- Limitations: Poor penetration; not suitable for rubber, plastics, or most medicines.
II. Moist Heat Sterilization
1. Core Principle
Utilizes the penetrating power of saturated steam to denature and coagulate microbial proteins. Significantly more efficient than dry heat sterilization.
2. Main Methods and Characteristics
- High-Pressure Steam Sterilization
- Parameters:
- Conventional mode: 121°C, 103.4 kPa (1.05 kg/cm²) for 15-20 minutes.
- Rapid mode: 134°C, 206.8 kPa for 7-10 minutes.
- Applications: Surgical instruments, culture media, rubber products, textiles, and other items resistant to high temperatures and pressure.
- Advantages: Strong penetration, thorough sterilization, and short processing time.
- Limitations: Not suitable for oils, powders, or heat-sensitive materials.
- Pasteurization
- Parameters:
- 60-85°C for 15-40 seconds (HTST method) or 30 minutes (LTLT method).
- Applications: Food products such as milk and alcoholic beverages; kills pathogenic bacteria but retains some non-pathogenic microorganisms.
- Advantages: Minimizes loss of heat-sensitive nutrients.
- Limitations: Not a complete sterilization method; requires refrigeration for storage.
- Ultra-High Temperature Instantaneous Sterilization (UHT)
- Parameters: 138-150°C for 2-5 seconds.
- Applications: Liquid foods (e.g., aseptically packaged soy milk, fruit juice).
- Advantages: Achieves commercial sterility while retaining over 90% of nutrients (e.g., only 3-4% loss of vitamin C).
- Limitations: Requires aseptic packaging technology; high equipment costs.
III. Comparison Between Dry Heat and Moist Heat Sterilization
Comparison Dimensions:
1. Sterilization Efficiency
- Dry Heat: Lower (requires higher temperatures/longer times).
- Moist Heat: Higher (rapid penetration of microorganisms).
2. Suitable Materials
- Dry Heat: Glass, metal, oily substances.
- Moist Heat: Rubber, plastics, liquid culture media.
3. Risk of Thermal Damage
- Dry Heat: High temperatures may cause oxidation and brittleness.
- Moist Heat: High-pressure steam may deform heat-sensitive materials.
4. Typical Applications
- Dry Heat: Laboratory glassware, injection oils.
- Moist Heat: Surgical instruments, food sterilization, medical dressings.
5. Sterilization Time
- Dry Heat: 2-4 hours (at 160-170°C).
- Moist Heat: 20 minutes (at 121°C).
IV. Selection Criteria and Considerations
- Heat Resistance of Items:
- Use dry heat for items resistant to high temperatures and sensitive to moisture (e.g., glass syringes).
- Use high-pressure steam sterilization for items resistant to pressure and moisture (e.g., surgical instruments).
- Sterilization Thoroughness:
- Prefer moist heat sterilization when killing spores is required (e.g., high-pressure steam at 121°C).
- Operational Convenience:
- The food industry tends to favor UHT to balance sterilization effectiveness and nutrient preservation.
- Equipment Limitations:
- Dry heat sterilization requires a specialized drying oven, while high-pressure steam sterilization requires an autoclave.
The choice of high-temperature sterilization method should be based on a comprehensive consideration of item characteristics (heat resistance, material), sterilization goals (e.g., whether spore elimination is necessary), and application scenarios (medical, food, laboratory). Dry heat sterilization is suitable for moisture-sensitive, high-temperature-resistant items, while moist heat sterilization is highly efficient and versatile, with high-pressure steam sterilization being the gold standard for medical sterilization.
