EFFECT OF MODIFIED ATMOSPHERE PACKAGING ON THE TVB TMA-PRODUCING MICROFLORA OF COD FILLETS/

Cod fillets (Gadus morhua) were packed under modified atmospheres, wit h four different gas compositions (60% CO2-10% O-2-30% N-2, 60% CO2-20 % O-2-20% N-2, 60% CO2-30% O-2-10% N-2, 60% CO2-40% O-2), and stored a t 6 degrees C. Plate counts were carried out after 3, 4, 5, 6 and 7 da ys, to follow the growth of aerobic and anaerobic bacteria, lactic aci d bacteria, H2S-producing bacteria and Enterobacteriaceae. The product ion of total volatile bases (TVB) and trimethylamine (TMA), and the ch anges in pH of the fillets were measured. Modified atmosphere packagin g (MAP) had in general an inhibitory effect on the growth of the micro flora but limited inhibition of the production of TVB and TMA. Despite the fact that increased oxygen proportions in the atmosphere contribu ted in a slightly lower production of TMA, all the samples had a TVB a nd TMA content high enough to be considered as spoiled after 4 days' s torage at 6 degrees C. A total aerobic plate count at 25 degrees C of a 10(6) cfu/g, combined with the presence of only a 10(3) cfu/g of H2S -producing bacteria, which are normally considered as TMAO-reducing or ganisms in fish, cannot explain the strong increase in TMA. A high cel l concentration of more than 10(8) cfu/g of Shewanella putrefaciens is required for production of a TMA level normally found in spoiled fish . This suggests that there could be another type of bacterium in fish, not involved in the spoilage of unpacked fish, which is resistant to 60% CO2, is not H2S-producing, and shows a high TMAO-reducing capacity . This bacterium could be Photobacterium phosphoreum.