Privatsphäre-Einstellungen

Steuerung der Dampfsterilisation auf der Grundlage des exponentiellen Standardmodells

Teil 1: Exponentielles Standardmodell und Steuerung der Sterilisation auf einen vorgegebenen SAL-Wert

Udo Franke

Korrespondenz: Dr. Udo Franke, Sonnenhalde 10, 72813 St. Johann (Germany), e-mail: udofranke@t-online.de

Control of Steam Sterilisation based on the Exponential Standard Model

In steam sterilisation processes targeted at specified F0 values, any marked deviation of sterilisation temperature (plateau temperature) and of target microorganism specific z values from the reference values (Tr = 121 °C; z = 10 °C) of the F0 concept leads to discrepancies between calculated and true lethality values. The following article describes a method for steering the sterilisation process towards a defined SAL value by which this error potential is minimised, thus enhancing sterilisation safety. Both the method described herein and the F0 concept itself are based on the exponential standard model. This model comprises the first-order rate law, the Arrhenius equation and the Bigelow model, which can be derived from the latter.
The sterilisation process is steered towards the specified SAL value by continuously calculating the inactivation of a hypothetical population of thermoresistant microorganisms (bacterial spores) characterised by the parameters N0 and kr. The sterilisation phase is terminated as soon as the specified SAL value has been reached. Lethality is calculated on the basis of a species-independent, cyclespecific kl (z) value which is obtained on the assumption of a minimum lethality level, thus ensuring that the following relationship holds throughout: F true
F calculated.
The determination of parameter kr (Dr) under isothermal or nonisothermal conditions involves non-linear functions which for the sake of ease are often converted to linear functions from which kr can be found by linear regression. However, it must be considered that this conversion only yields an approximation rather than the true value of parameter kr.
The article describes a method for determining kr under conditions identical or very close to those which occur in real sterilisation cycles.

Key words Inaktivierungskinetik, exponentielles Standardmodell, F0-Konzept • Letalität, Letalitätsparameter, Letalitätsminimum, Geschwindigkeitskonstante • Sterilisation, Dampfsterilisation, Sterilisationssteuerung • Sterilisationssicherheit, SAL