Abstract
Contamination by Listeria of frozen red salmon and smoked salmon was investigated. Although none of the 60 samples of frozen red salmon were contaminated with Listeria, 23 out of 76 smoked salmon samples (30.3%) were contaminated. L. monocytogenes was detected in 12 of the positive samples. Other species identified were L. welshimeri, L. innocua and L. seeligeri. The serotypes of isolated L. monocytogenes were 1/2a, 1/2b, 1/2c, 3a, 3b and 4b.
The end product of smoked salmon was stored in an aerobic or an anaerobic package at 2°C and 10°C to experimentally trace the behavior of L. monocytogenes. In samples stored at 2°C the initial count of 102/g increased to 104∼105/g in 10 days and to 108/g in 20 days. In samples stored at 10°C, the number increased to 107∼108/g in 5 days. The growth was somewhat inhibited in anaerobic conditions when compared to aerobic conditions. In samples stored at -20°C for 6 months, the initial count of 104∼105/g showed a decrease in the order of one in either raw or smoked salmon.
