Explorative multivariate analyses of 16S rDNA microbial community data from modified atmosphere-packed (MAP) salmon and coalfish

Sammendrag

Packing foods in a modified atmosphere (MAP) in combination with low temperature storage extends product shelf life by limiting microbial growth. We investigated the microbial biodiversity of MAP salmon and coalfish using an explorative approach, analyzing both the total amounts of bacteria and microbial group composition (both aerobic and anaerobic). Real-time PCR analyses revealed a surprisingly high difference in the microbial load for the different fish samples. The microbial composition was determined by partial 16S rDNA sequences from 180 bacterial isolates, in addition to tRFLP and cloning of 92 sequences from PCR products of DNA directly retrieved from the fish matrix. Twenty different bacterial groups were identified. Partial Least Square (PLS) regression was used to relate the major groups of bacteria identified to fish matrix and storage time, respectively. A strong association of coalfish with Photobacterium phosphoreum was determined. Brochothrix spp. and Carnobacterium spp., on the other hand, were associated with salmon. These bacteria dominated the respective fish matrixes after the storage period. Twelve Carnobacterium isolates were identified as either C. piscicola (5 isolates) or C. divergence (7 isolates), while the 8 Brochothrix isolates were identified as B. thermosphacta by full-length 16S rDNA sequencing. The Principal Component Analyses (PCA) and PLS of the growth characteristics (49 different substrates) showed that C. piscicola had distinct substrate requirements, while the requirements for B. thermosphacta and C. piscicola were quite divergent. In conclusion, the explorative multivariate approach gave a more comprehensive picture of the total microbial biodiversity in MAP fish than previously possible. This knowledge is crucial in controlled food production using e.g. the Hazard Analysis Critical Control Points (HACCP) principle.