Reduction of trimethylamine oxide by Shewanella spp. under modified atmospheres in vitro

Two strains of Shewanella spp. were isolated from cod fillets packed in modified atmosphere (60% CO2, 30% O-2, 10% N-2). One of the strains was identified as Shewanella putrefaciens. The other strain could not be fully identified but was determined as a Shewanella spp. different from S. putrefaciens. The effect of modified atmosphere (CO2, O-2) on the growth of the two strains and on the reduction of TMAO to TMA was studied using solid medium 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. The Shewanella-like strain was shown to be a stronger TMAO reducer and was more resistant to CO2 than S. putrefaciens per se. Modified atmosphere packaging of marine fish can inhibit the growth and TMAO-reducing activity of S. putrefaciens when 50% of CO2 together with 10% of O-2 are introduced into the packaging atmosphere. The growth and TMAO-reducing activity of the Shewanella-like strain can be inhibited when higher proportions of CO2 together with as high as possible proportions of O-2 are introduced into the packaging atmosphere. It is suggested that a combination of 60-70% CO2 and 30-40% O-2 is introduced into the packaging atmosphere in order to prevent TMA production by Shewanella spp. (C) 1997 Academic Press Limited.