Absence of Listeria monocytogenes growth during raw milk cheesemaking: a modelling approach

The presence of Listeria monocytogenes in certain foods and the risk that this poses
to public health and food quality is still a problem. Currently, the field of food mi-
crobiology focuses on obtaining data on the behaviour of microorganisms in food,
but the responses obtained provide little insight into the relationship between
physiological processes and growth or survival. This link can be made through
mathematical models. In a simple form, a mathematical model is a simple mathe-
matical description of a process. The application of mathematical models to food
microbiology has been developed in recent years and now constitutes a new disci-
pline named as Predictive Microbiology. However, most predictive models are
based on laboratory experiments in microbiological media under static conditions.
As such models tend to be inaccurate, we have undertaken our experiments in a
food system under dynamic conditions. Cheese was made with raw and pasteurised
milk deliberately contaminated with L. monocytogenes
.
Listeria was monitored through the manufacture and ripening period of the cheese. The results showed
that L. monocytogenes did not grow during manufacture of raw milk cheese, but
did grow during manufacture of pasteurised milk cheese. The data obtained for
growth, survival and inactivation was modelled. The application of models that
can explain the behaviour of Listeria in cheese and the further predictions that
can be obtained from these models are useful for the improvement of ongoing re-
search on biotraceability and for the better understanding of the general behaviour
of these microorganisms under dynamic conditions, such as in dairy products