ml or cfu/cm2 (NOT on a log scale) and log Growth is the log increase
due to growth. Note that if the food product is not
contaminated after recontamination, Nf2 equals zero and growth is
not possible: Nend will be zero too.
Clearly, if log Red is high, Rec is low and log Growth is low, the
process is well under control and the concentration in the finished
product will be (very) low. If processes that should ensure inactivation
and prevention of recontamination and growth are effectively
controlled and show excellent historical records, finished
product testing can add little to the control of safety.
6. Case studies on products
In this paper, the production processes of three different types of
food products are presented as three case studies: canned food
(specifically considering Clostridium botulinum), chocolate (specifically
considering Salmonella spp.) and cooked sliced ham (specifically
considering Listeria monocytogenes). The processes have
different characteristics in terms of reduction, recontamination and
growth and therefore put different demands on food safety control
and management. For the three case studies the role of the finished
product testing is evaluated and it is hypothesised that identification
of the impact of process steps that may lead to reduction,
recontamination of growth can be used as tool to assess the
importance of sampling and control in the process. This is studied
by analyzing the available data.
7. Canned products
For foods that are sterilised in hermetically sealed cans (Fig. 3),
generally a minimal F121C value of 3 min (at the slowest heating
point) is used to guarantee sufficient reduction of C. botulinum
spores (for low-acid products). For an often assumed D121C value of
0.21 min (Bean et al. 2012), this results in a 14.3 log reduction. This
means virtually absence of the organism. If initially 100 spores of
the organism would be present in a can, only 1 in 1012 cans would
have a survivor present (Bean et al. 2012). This is in the same order
as the yearly world can production. If different initial levels are
assumed of course a different defect rate is obtained, however with
>12D processing, very low probabilities of survival are obtained.
For acid foods lower F121C values can be accepted, resulting at
these lower pH values also in a >12D reduction, since the D121C at
lower pH values is smaller than at neutral pH (and additionally
C. botulinum is not able to grow at pH < 4.6 (Bean et al. 2012)). In
order to also control food spoilage often producers use higher F121C
values, especially for products where the intrinsic properties can
increase the heat resistance of spores like presence of fat.
If the can is perfectly sealed, no recontamination can occur, and
the number of organisms is totally determined by the level of
surviving organisms. However, if the sealing is not perfect, generally
other contaminants than C. botulinum will re-contaminate the
product. As the environment where this contamination will take