The presented method has been developed to assess the potential
growth of C. perfringens during the cooling down process of
cooked dishes in catering. A probabilistic approach has been used in
order to take into account the variability of the factors impacting
the result. This method is useful to evaluate both the effects of
manufacturing practices (kitchen organization, food workers
practices and equipment characteristics) and the influence of the
process criterion (blast chiller piloting by a temperature probe).
The cooling process performance evaluation only requires simple
measuring equipments and can be performed under usual working
conditions of the kitchens. Technical organizations being competent
in probabilistic calculations are able to perform these tests.
But in return this method presents some uncertainty about the
achieved values of bacterial growth. This is mainly related to
possible differences between the measured temperatures and the
actual temperatures and to the lack of accurate scientific data about
the value of the lag phase of C. perfringens spores. Calculated
growth values can thus differ from the actual values. However, they
are close and are useful to assess the microbiological safety of the
process.
So, this method can be used to validate the cooling process in
the context of the implementation or the revision of the HACCP
plan. In that case, the responsibilities must be clearly defined between
the kitchen manager and the technical organization performing
the tests. This one must indicate the operating conditions
under which the validation is relevant. The kitchen manager is
responsible for the compliance with these conditions during the
manufacturing operations. This has to be checked especially when
there is an important change in the working organization or in the
equipments. This test method requires the determination of a
probabilistic criterion of acceptability, i.e. to define the maximum
probability of exceeding the limit chosen for bacterial growth (for
example 1 log10). If this criterion is not specified by the health
authorities, it must be determined by experts who will take into
account the characteristics of the whole process and the initial
microbiological quality of raw materials.
Finally, the validation of the cooling process must be done with
caution, as the variability of the parameters that influence the
growth of C. perfringens is difficult to assess during a few days tests
in a kitchen.