Caractérisation et quantification moléculaires de l’écosystème microbien d’altération du saumon cru et des crevettes cuites

Raw salmon and cooked shrimp sold in supermarket are usually found under vacuum or CO2 modified atmosphere packaging (MAP). This type of packaging inhibit growth of some bacteria, therefore, CO2 tolerant bacteria dominate spoilage microbiota of these products. The aim of this study is to improve knowledge about bacteria involved in spoilage. Spoilage microbial ecosystems of raw salmon and tropical cooked shrimp were described using classic miocrobiological and molecular methods like PCR-TTGE and pyrosequencing. Lactic acid bacteria, notably Lactococcus piscium, Carnobacterium maltaromaticum, Carnobacterium divergens, Lactobacillus sakei, and Gram negative bacteria like Photobacterium phosphoreum and Enterobacteriaceae (Serratia spp.) has been described as dominant bacterial groups on spoiled MAP salmon by using both type of methods. Shewanella baltica and C. maltaromaticum were mostly present in spoiled entire tropical cooked shrimp while, Carnobacterium spp., Leuconostoc spp. and Streptococcus parauberis dominated spoiled peeled tropical cooked shrimp analyzed with pyrosequencing. In order to identify the bacteria responsible for these products spoilage, spoilage potential of several of these species was investigated using sterile matrix inoculation. Then, combining sensory, chemical, microbiological and molecular methods, spoilage of the inoculated samples was characterized. Volatile compounds analysis (GC-MS) of some samples was also realized. C. maltaromaticum and S. baltica are both implied in entire tropical cooked shrimp spoilage and P. phosphoreum was revealed to be responsible for MAP salmon spoilage. As no specific medium is available for enumeration of P. phosphoreum species in seafood products, a real time PCR method combined with propidium monoazide treatement was , thus, developed and used to quantify viable cells of this bacteria in salmon samples.