How to validate a pasteurisation or sterilisation process

By: Nine Pijl and Frank de Bok

If a new pasteurisation or sterilisation step has been implemented or changed, how can we be sure that the product is food safe? Performing proper process validation beforehand can help with this. But what exactly is proper process validation?

Process validation is always performed before production takes place according to the new process. The validation is carried out both theoretically and practically.

In a theoretical validation, the various properties of the products are mapped out. The pathogen reduction and growth are in fact strongly dependent on properties such as Aw, pH and salinity. It is assessed which and how many pathogens must be reduced or killed off, in other words, what is the purpose of the pasteurisation or sterilisation. Legislation and specific customer requirements are also taken into account. The technical information and the settings of the installation are used to determine whether the required reduction is achieved, possibly supplemented with historical data from the same installation, if available.

A theoretical validation, taking into account the worst-case scenario, may be sufficient to cover the risk of a food safety hazard, but a practical validation for pathogen-reducing process steps such as pasteurisation and sterilisation is just as important. Testing the installation with the product and checking the desired outcome can prevent unexpected or misjudged risks. Due to the lack of practical validation, in practice too high levels of contamination are sometimes found or even recalls are carried out because the installation did not do what was theoretically expected.

Two practical validations can be performed: validation of the process equipment and validation of the product.

The process equipment is validated in various respects, such as temperature range, temperature distribution, time, etc. This is usually done by the supplier of the equipment.

During a validation of the product, the product is deliberately contaminated with a pathogen (the target organism) that the process must eliminate, after which the process is run. By quantifying the target organism before and after the process step, it can be assessed whether the process does what is expected of it. Sounds simple, but how do we go about this?

A product validation can be performed according to two different methods. Method 1 is to simulate the process in a laboratory and the second method is to perform the validation at the company.

When the validation is performed in the laboratory, a known amount of pathogen is added to the product. After this, the product is heated on the basis of data from the company, whereby reduction of the pathogens will occur. A new count is then performed to determine the reduction of the pathogen. The outcome is then compared with the theoretical validation. When the results are in accordance with the requirements and expectations, it can be concluded that the hazards are under control and that production can be carried out safely. However, there is a challenge: how do you simulate the process conditions in the laboratory?

Validation is more accurate if the same pathogen contamination process is carried out at the company itself and with the installation that is to be used. The advantage of validation in the company itself is that certain measurement uncertainties and fluctuations in the process, such as changes in flow and discharge, are automatically included. These factors are sometimes unaccounted for in the theoretical validations, but they certainly have an influence on the reducing capacity of the pathogens. It is also often not possible to fully simulate the process conditions in the laboratory. However, it is not without risks to use a pathogen in a process. A clear protocol must be drawn up so that all risks are identified and any unintended contamination of the product is eliminated. To limit the risks, a so-called surrogate organism is often used. To do this, it must first be demonstrated in the laboratory that the reduction of this surrogate organism is comparable or less than that of the target organism. For such studies, a specific strain of Enterococcus faecium is often used, which is known to be slightly more heat-resistant than Salmonella.

When a process validation is carried out correctly beforehand, all risks in the process are mapped out and food safety is guaranteed. This avoids having to carry out recalls, with the consequent financial and reputational damage. It also helps save unnecessary repair costs; when an error is detected early, the repair costs are often much lower.


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