Product category:
Plant Inspection and Cleaning
News Release from: Signatrol | Subject: F0 Sterilisation
Edited by the Processingtalk Editorial
Team on 19 March 2008
Assisting optimisation of sterilisation
processes
The Signatrol Temp-IT universal data logging software now has F0 calculation functionality, specifically developed for the validation of anti-bacterial steam sterilisation and cooking processes
The company believe their family of temperature data loggers are the first portable units to offer this important capability, effectively automating sterilisation calculations as well as providing the all important electronic traceability Ensuring the temperature versus time accuracy of steam steriliser processes is a vital food safety issue
This article was originally published on Processingtalk on 22 Jan 2003 at 8.00am (UK)
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It is clear that companies and organisations carrying out any sterilisation need to ensure that any risk of harmful micro-organisms is minimised to what are termed as 'acceptably low levels.' However excessive 'belt and braces' sterilisation to ensure compliance is not only time consuming, but also expensive and energy inefficient.
In parallel, over-sterilisation can adversely affect product taste and quality.
The Signatrol solution offers a number of important benefits and allows the point at which ideal sterilisation is achieved to be read directly from the Temp-IT chart.
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This enables the process engineer to optimise his process, thus saving cost, and the QA manager to look at existing processes and satisfy himself that the sterilisation is such that all bugs are killed (or rather reduced statistically to an acceptable level).
The industry-standard optimised operating temperature for sterilisers has long been established as 250degF or 121.1C.
F0 is defined as the time during which sterilisation needs to be performed at 121.1C, or the time during which sterilisation needs to performed at another temperature, (related by calculation to 121.1C) so as to provide the equivalent lethal heat dose for effective microbial destruction.
The importance of accurate temperature measurement and control is put into perspective when calculation shows that if the sterilising temperature is just one degree below 121.1C, the required sterilisation time increases by 25%.
Up until just a few years ago, it was thought that steam sterilisation provided a complete barrier against harmful micro-organisms.
In other words, once a certain temperature was reached and maintained for a certain time, all the micro-organisms contained in a so called 'unit' or container would die within that time, regardless of their number.
The risks of such an assumption are starkly evident.
More recently it has been shown that steam sterilisation actually proceeds like a first-order chemical reaction and therefore at a specific rate which is higher or lower as the temperature rises or falls.
It is also a function of the number of micro-organisms present in the unit.
This rate can be expressed as a decimal decay time 'D' which is the time at which the sample must remain at 121.1C in order for the micro-organisms to be reduced to one tenth the number originally present.
'D' is typically in the range 0.5 to 2 minutes and is commonly taken to be 1 minute, this being a typical average.
Statistical calculation shows that at the end of each minute of permanence at 121.1C, the number of micro-organisms reduces to one tenth of the number at the beginning of that minute.
Therefore, if a unit vial or bottle is kept at 121.1C for three minutes, the number of micro-organisms contained therein is reduced to one thousand (1/10 x 1/10 x 1/10 = 1/1,000) of the initial number.
Following this progression, if the initial bacterial load of a batch of units being sterilised averages 1,000 (i.e.1000 micro-organisms per), after three minutes of treatment at 121.1C the number will be reduced on average to 1: After a further minute of sterilisation (four minutes altogether) this reasoning leads one to the conclusion that the bacterial load has dropped to 1/10, i.e 0.1.
However, this must not be understood to mean that at this point each unit contains one tenth of a micro-organism (in which case the units would be sterile) moreover it must be taken to mean that there is a probability that 1/10 of the units are still contaminated.
After nine minutes of treatment at 121.1C, the bacterial load of the batch at issue is reduced, on average, to 1/1,000,000, i.e.10e-6.
The probability of still having a contaminated unit in that batch is therefore 1 in 1,000,000.
This is the minimum assurance of sterilisation normally required although higher levels, especially in the pharmaceutical industry of up to 10e-9 (1 in a billion) are sometimes specified.
The effective sterilisation time is therefore selected to ensure the desired reduction in micro-organisms to an acceptable level.
The problem in the real world is that the temperature is never exactly 121.1C.
The process warms up and cools down and these periods effectively contribute to the sterilisation process.
The relationship between the real world temperature and the ideal 121.1C is computed within the F0 calculation.
Using the F0 calculation within TempIT enables an accurate log of the sterilisation process to be made and recorded as part of the product record or for system validation.
Placing two markers on the subsequent trace enables the F0 to be read off between the markers in minutes.
In this way the exact point in the sterilisation cycle where the desired reduction in micro-organisms had been first achieved is pinpointed.
After this point no further sterilisation is necessary, or indeed desirable, and so the process can be modified to reduce the sterilisation cycle time and so optimise energy usage whilst maintaining product quality and, more importantly, product safety.
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