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A successful sterilization kills microorganisms or destroys infectious proteins, viruses etc.
A sterilization process enables the sterilization probability to be increased almost at will. 0 microbes/part cannot however be reached.
A sterilization probability (sterility assurance Level SAL ≤ 10-6 = 1:1 Mio.) was specified in the European Pharmacopeia. If this SAL is complied with, the product is described as “sterile”.
In sterilizing temperature-sensitive products the sterilization time may have to be reduced to a minimum at a specified temperature dependent on the product-specific D* value, which can be determined experimentally, and the z-value**, in order to avoid adversely affecting the quality of the product or even destroying it.
In practice any possibly negative effects of an excessively long exposure to heat can be established for example by checking whether any dark discolorations are formed on agar.
Even if such a dark discoloration does not necessarily make the agar unusable, it still represents a visual shortcoming which is in most cases undesirable.
The required sterilization times can be minimized by calculating the F0 – value. The F-value indicates the sterilization times at a constant temperature. This means the F-value can be expressed as sterilization work within a certain sterilization process and is expressed in minutes at a specific temperature. The sterilization time for reaching a certain final bacterial count can be calculated at a given F0 value which is specified as a reference for many industrial processes at a sterilization temperature of 121°C and a z value of 10°C.
Under conditions of actual use the autoclave heats the product over a certain time until the sterilization temperature of e.g. 121°C is reached. Microorganisms are killed during the heating time of 100°C to 121°C as well as during the cooling time. The dwell time can be correspondingly shortened taking into account this germicidal effect during the heating and cooling time. This enables the F-value aimed for to be reached in a shortened overall procedure time, provided the “coldest or the most difficult point” to sterilize in the load has been determined beforehand. (European Pharmacopeia)
*Der D-Wert gibt an, wie lange ein Sterilisationsprozess auf die Mikro-Organismen einwirken muss, um eine Reduzierung der Keimzahl um eine Zehnerpotenz bzw. 90% der Ausgangskeimzahl zu erreichen. **Der z-Wert beschreibt, wie sich die Abtötungsgeschwindigkeit der Mikroorganismen mit der Temperatur verändert.