UNPACKAGED SLICED FRANKFURTER-TYPE SAUSAGE - BEHAVIOR OF LISTERIA-MONOCYTOGENES

Unpackaged sliced frankfurter-type sausage (160 samples) was bought in 8 shops (5 small shops, 3 supermarkets) and examined for listeriae. Listeria spp. were detected in 54 samples (34%) and Listeria mono cytogenes in 31 samples (19%). The bacterial count for L. monocytogenes was below 10/g in 30 samples and between 10 and 100/g in one sample. In sliced frankfurter-type sausage that had been made experimentally and inoculated with L. monocytogenes a 2 to 4 powers often with of listeriae was observed in the course of a week at 7-degrees-C, whereas there was no growth at a storage temperature of 2 or 4-degrees-C. When commercial sliced frankfurter-type sausage was inoculated with L. monocytogenes there was only a relatively small growth (of up to 2 powers of ten) even at 7-degrees-C. This was attributed mainly to the competing flora, since when the sausage is sliced in the shop it is contaminated with lactic acid bacteria on average with 10(4)/g. Listeriae growth is more or less severely inhibited, depending on the acidifying power of these contaminants but growth of 2 to 3 powers of ten within a week at 7-degrees-C seems to be the rule. On the other hand the addition of 0.1% sodium acetate to the frankfurter-type sausage mixture, which is what the food regulations allow, will inhibit listeriae sufficiently during the storage of the sliced product up to the stage of sensory spoilage. In practice sodium acetate is already sometimes added to frankfurter-type sausage and our investigations suggest that its general use can be recommended since, when using sodium acetate, the presence of low bacterial counts of L. monocytogenes (up to 100/g) would also be tolerable in frankfurter type sausage because, as with raw meat products, no serious growth of listeriae is to be expected, even in unpacked frankfurter-type sausage.