In vitro study of TMAO reduction by Shewanella putrefaciens isolated from cod fillets packed in modified atmosphere

A strain of Shewanella putrefaciens was isolated from cod fillets in a modified atmosphere (60% CO2, 30% O2, 10% N2). The effect of pH on the growth of Shewanella putrefaciens and TMAO reduction was studied in fish extract with citrate buffer systems at pH values from 5.8 to 6.8. The effect of the modified atmosphere (CO2, O2) on the growth of S. putrefaciens and on the reduction of TMAO to TMA was studied using solid media from fish extract packed under variable mixtures of CO2, O2 and N2. All the samples were incubated at 7 degrees C for 7 days. Slow development of S. putrefaciens and no production of TMA was observed in fish extract buffered at pH 5.8. Inclusion of O2 in packaging atmosphere of solid fish extract, even at small proportions (10%), was inhibitory for the reduction of TMAO, while there was no effect of O2 on the growth of S. putrefaciens. Increased levels of CO2 (> or = 50%) in the atmosphere were inhibiting the growth of S. putrefaciens and consequently the production of TMA.