EFFECTS OF AUTOCLAVING ON FERMENTORS

Most fermentors are sterilized by autoclaving, or hot steam under pressure. For small laboratory fermentors they are sterilized in autoclaves. In the case of large fermentors, most if not all are equipped with in situ sterilization facilities built into the fermentor system.

For most autoclaving sterilizations for both small and large fermentors, the accepted autoclaving conditions is at 121 degrees Centigrade at pressure of 15 to 20 psi. The autoclaving holding time about 15 to 20 minutes.

For very large industrial fermentors, depending on various other factors as loading and target kill, the sterilization regimes could be different or individually determined.

During sterilizations by autoclavings, the fermentors and its contents are subjected to very high temperature, pressure and long contact time. The fermentors undertaking the sterilization will be subjected to a high degree of physical abuse and the reactions of the fermentor could be as follows

1 There will be expansions in the volume of the fermentor as materials expand under high temperature. The fermentor will face additional problems as the structure of the fermentor is made up of various materials such as glass, steel, rubber etc. Each of the component material will show different coefficient of expansions

2 High heat will cause water to evaporate. So it is not surprising that there will be a loss of water from the fermentation broth by a few percent. The loss of water will either result in:

a) the broth being more concentrated or
b) there will be an increase in the surface area to volume ration of the content of the broth leading to faster evaporation rates

In making up for the loss of water additional water has to be added to compensate for the potential loss of water by autoclaving

3 There will be a degree of nutrient degradation especially for sensitive labile organic compounds

4 There will be unwanted side reactions such as between sugars and amines leading to the toxic Maillard's reactions

TOWARDS PROPER AUTOCLAVING OF FERMENTORS
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An autoclave in simplicity is just a more complex pressure cooker. To be efficient in autoclaving it is very important to drive off any air pockets that might be present in the autoclave. Air is a poor heat conductor. If the air is not driven out it will be difficult to bring the right temperature in all the autoclave. Let the autocleave heat and steam up and release the hot steam through an escape valve before closing the valve and starting the sterilization process

Ensure that the temperature recorded in the autoclave chamber is uniform throughout the whole chamber. Make sure the temperature stated on the panel outside the autoclave is the real temperature inside the autoclave chamber. We do not want under heating and over heating to occur. Place thermo probes to measure the real temperature of the autoclave and repair if needed

Do not overload the autoclaving chamber. This might lead to poor degree of sterilization being achieved.

Ensure that the autoclave is not leaking or suffering from leak in pressure as it will affect the sterilization process