Growth and metabolic activity of Shewanella putrefaciens maintained under different CO2 and O2 concentrations.

Growth, trimethylamine (TMA), off-odour and biogenic amine production by a strain of Shewanella putrefaciens isolated from spoiled hake (Merlucius merluccius L.) and cultured in a model system, were tested under four different gas compositions (60% CO2/40% O2, 60% CO2/15% O2/25% N2, 40% CO2/60% O2, 40% CO2/40% O2/20% N2) and under air. After 3 weeks of incubation, the control (air) batch showed the highest microbial counts (> 9 log cfu/ml) and TMA concentrations (45 mg N-TMA/100 ml), and strong putrid off-odours were detected from day 15. High amounts of putrescine and cadaverine were produced in this batch, but histamine increased only slightly. Batches under controlled atmospheres showed reduced growth, TMA, off-odour and biogenic amine production. The 40% CO2/60% O2 mixture had the strongest inhibitory effect on bacterial growth, while the 60% CO2/15% O2/25% N2 mixture was less effective. Putrescine and histamine production was lowest in S. putrefaciens under the 40% CO2/60% O2 mixture. However, the level of histamine in S. putrefaciens was higher under 40% CO2/40% O2/20% N2 than when the bacteria was incubated in air. Under the gas mixtures, there was a similar decrease in the production of cadaverine and agmatine by S. putrefaciens, irrespective of the gas concentrations. The production of 2-phenylethylamine appeared to be inhibited under any atmospheric condition.