Amino acid-decarboxylase activity in bacteria associated with Mediterranean hake spoilage

We examined the amino acid-decarboxylase activity of bacteria isolated throughout the ice storage of Mediterranean hake. Pseudomonas was the main microbial group in the fresh samples. Its number increased by up to 2 logarithmic units during the storage and 20% of the isolates showed the ability to produce putrescine. Shewanella putrefaciens was the most prolific organism and became the dominant microbial group on day 6 of storage. It also had the highest proportion of aminogenic isolates and the strongest decarboxylase potential as a tyramine- and cadaverine-producing microorganism. A competitive procedure in biogenic amine production seems to have occurred when trimethylamine oxide was available in the culture medium. The abundance of Enterobacteriaceae increased gradually throughout the storage but never reached high counts and their isolates produced small amounts of cadaverine only. Although the counts of micrococci and staphylococci were considerably high, only two isolates were ornithine-decarboxylase positive. Neither lactic acid bacteria nor enterococci were positive.