Sterilization is the process of killing or removing all viable microorganisms, ensuring that only the desired production strain thrives in the fermenter.
Common Sterilization Techniques
1) Heat Sterilization (Thermal)
A) Moist Heat (Autoclaving)
Uses steam under pressure (usually 121 °C at 15 psi for 15-20 minutes in a lab setting).
At industrial scale, in-situ sterilization in large reactors may involve higher temperatures and times that depend on scale.
B) Dry Heat
Hot air ovens at 160-180 °C. More common for glassware and metal equipment.
Filtration
For temperature-sensitive media components (e.g., vitamins, enzymes) or for sterilizing incoming air.
Membrane filters (0.2 μm) remove bacteria and most contaminants.
Chemical Sterilization
Chemicals like ethylene oxide, peracetic acid, or bleach can disinfect surfaces.
Rare in industrial fermentation due to residues and potential toxicity.
UV Radiation
Sometimes used to sterilize surfaces or air in certain chambers, but not common for liquid media at large scale.
Key Considerations
Sterilization Time and Temperature: Must be high/long enough to eliminate contaminants yet not so high or long as to degrade the medium significantly.
Validation: Verification that sterilization conditions consistently achieve complete sterility.
