6.6 Incubation Tests
Although they should not be used as the sole criterion of product safety, incubation tests can provide valuable information as to the adequacy of the thermal process and also a means of monitoring (indirectly) the microbiological 1 quality of in-coming raw materials.
Should a process be of marginal severity, so that a measurable proportion of the population of spore-forming thermophilic bacteria survive, it may be possible to detect changes in the incidence of spoilage after thermophilic incubation tests on the production samples which have been collected as part of routine quality control. It is difficult to predict the level of spoilage in the trade which correlates with a known incidence of spoilage arising from incubation of test samples; however, it was reported by Stumbo (1973) that a thermophilic spoilage level of 1% after thermophilic incubation was found in commercial practice to give rise to a spoilage rate of 0.001% (i.e., 1 in 100 000 units) in the trade. Should a fish canner be able to collect sufficient data to draw their own conclusions concerning the relation between spoilage induced by thermophilic incubation and trade spoilage, the value of these incubation tests becomes clear; particularly for those manufacturers whose products are expected to be marketed in warm climates.
Under normal circumstances there would be little point in routinely monitoring spoilage arising from mesophilic incubation as all the spores which might lead to growth under these conditions should have been eliminated by thermal processes in which target Fo values are 10 to 15 min. However, if there are incidences of mesophilic spoilage detected by these test measure it is reasonable to conclude that there has been either a significant lapse in the microbiological quality of the raw materials, or a gross failure in delivery of the scheduled thermal process (see Table 3 for a summary of factors that could lead to this phenomenon). such circumstances corrective remedial action should follow immediately and, suspect stock should be isolated pending a detailed examination.