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% O-2, 10% N-2). The effect of pH on the growth of Shewanella putrefaciens and TMAO reduction was studied i n fish extract with citrate buffer systems at pH values from 5.8 to 6. 8. The effect of the modified atmosphere (CO2, O-2) on the growth of S . putrefaciens and on the reduction of TMAO to TMA was studied using s olid media from fish extract packed under variable mixtures of CO2, O- 2 and N-2. All the samples were incubated at 7 degrees C for 7 days. S low development of S. putrefaciens and no production of TMA was observ ed in fish extract buffered at pH 5.8. Inclusion of O-2 in the packagi ng atmosphere of solid fish extract, even at small proportions (10%), was inhibitory for the reduction of TMAO, while there was no effect of O-2 on the growth of S. putrefaciens. Increased levels of CO2 (greate r than or equal to 50%) in the atmosphere were inhibiting the growth o f S. putrefaciens and consequently the producing of TMA.