(2) The food receives some treatment that restricts the competitive
microflora and, in normal circumstances, should also control
C. botulinum.
(3) Conditions in the food (temperature, pH, Eh,aw) are suitable for
the growth ofC. botulinum.
(4) The food is consumed cold or after a mild heat treatment
insufficient to inactivate toxin.Since low-acid canned foods can fulfil all the above criteria, it has been
necessary for the canning industry to introduce stringent process control
measures to ensure safety (see Chapter 4). When canned foods are
produced as a small-scale, domestic activity however, greater variability
and less rigorous control are clearly potential sources of problems. In the
United States, where home-canning is more widely practised than else-
where, inadequately processed products, particularly vegetables, are the
most common cause of botulism. Between 1899 and 1981 there were 522
outbreaks associated with home-canned products, including 432
Figure 7.4 Mouse neutralization assay for botulinum toxin
206 Bacterial Agents of Foodborne Illness