Microbial growth in modified atmosphere packaged blue mussels (Mytilus edulis)
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Microbial growth was investigated in live blue mussels (Mytilus edulis) packaged in modified atmosphere (MA) and stored at -1 and 4 oC for 19 days. The mortality of mussels was 0.8 % after 19 days of storage with lowest mortality at -1 and in CO2 atmosphere. The increase in bacterial numbers in the mussel flesh was low, 1- 2 log units, measured as Aerobic Plate Counts, H2S-producing bacteria, and psychrotrophic bacteria. There was significant lower bacterial growth (p<0.05) in an atmosphere with CO2:O2 compared air and N2:O2 and at -1 oC. An initial level of < 3 mg Tri-Methylamine Oxid-N (TMAO-N)/ 100g was found in the mussels, detectable levels of trimethylamine-N (TMA) were observed after 11 days of storage and TMA-N increased to 1 – 3 mg/100g in 19 days. Total Volatile Nitrogen (TVN) increased from 3.4 to 18 mg/100g in 19 days and may be an important chemical indicator to be used in defining the shelf life. Low temperature (-1 oC) did not significantly increase the shelf life, but the superchilled temperature will control pathogenic growth. MA packaging of live blue mussels is a promising packaging technology for retail distribution, with a shelf life of 11-12 days based on sensory scores.