The exploration of dominant spoilage bacteria in blue mussels (Mytilus edulis) stored under different modified atmospheres by MALDI-TOF MS in combination with 16S rRNA sequencing

Few studies have addressed species-level identification of spoilage bacteria in blue mussels packed under modified atmospheres (MAs). We investigated the effect of MAs and seasons on the tentative species-level of dominant spoilage bacteria in blue mussels. Summer (s) and winter (w) blue mussels were stored at 4 degrees C in the atmospheres (%CO2/O-2/N-2): A40s (30/40/30), B60s (40/60/0), C60s (0/60/40), A40w (30/40/30), and D75w (25/75/0). In total, 122 culturable isolates were obtained at the final stage of shelf life, when mortality was high (56-100%) and total psychrotrophic bacteria counted >7 log CFU g(-1). Biochemical properties were analyzed using gram reactions, catalase and oxidase activities, and salt tolerance tests. Culturable isolates were identified through matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and 16 S rRNA gene sequence analysis. Spoilage potential tests were investigated by evaluating protease, lipase, and fermentation activities as well as gas and H2S production. The culturable isolates showed tolerance to varied salt concentrations. Psychromonas arctica, Pseudoalteromonas elyakovii, and Shewanella frigidimarina were dominating in specific MAs. Winter blue mussels resulted in a higher variation of spoilage bacteria, including S. frigidimarina, S. vesiculosa, S. polaris, Micrococcus luteus, Paeniglutamicibacter terrestris sp. nov., and Alteromonas sp.