Limited microbial growth in Atlantic salmon packed in a modified atmosphere

This study examined the dynamics of microbial growth in fresh chilled Atlantic salmon (Salmo salar) packed in a modified atmosphere. Atlantic salmon were harvested, handled, transported, and processed under optimal conditions to produce skinless fillet portions packed in pouches containing 96% CO₂ at gas: product ratios of greater than 5:1 (v/w) and stored for 38 days at less than 1 Celsius degree. Microbial analysis was conducted using psychrotrophic and mesophilic plate counts and DNA-based techniques. Results revealed initial microbial counts at day 0 of 10² CFU g^-1 and sequences from the genera Luteimonas, Pseudorhodoferax, Aequorivita, Gillisia, Gramella, Micrococcus, Acidovorax and Achromobacter. An extended lag phase was observed of 10 (psychrotrophic) or 15 (total) days with total plate count numbers reaching 10⁶ CFU g^-1 after 21 (psychrotrophic) and 25 days (total) and stabilising at 10⁸ CFU g^-1 after 31 days. At 31 days the microbial community was dominated by Pseudomonas spp. as determined by identification of isolates and sequencing of a 16S rRNA gene clone library. No Photobacterium spp., including the specific spoilage organism Photobacterium phosphoreum, were identified during the study.