University of Antilles, Martinique
Adèle Silbande is a PhD student in Food Microbiology research at the university of Antilles in Martinique. She works on the post-mortem microbial ecosystems of tropical fishes, Thunnus albacares and Sciaenops ocellatus, and the impact on the quality of the products (ECOSYSP). This research is realized with the PARM (Pôle agroalimentaire régional de Martinique) and Ifremer/EM3B (Ecosystèmes microbiens et molecules marines pour les biotechnologies) laboratories under the supervision of Dr. Françoise LEROI. She will defend her thesis work on December 2016 with four published or submitted papers on the subject.
The objective of this work was to describe precisely the bacterial ecosystem of the yellowfin tuna flesh widely consumed in Martinique. In addition to the culture-dependent methods, a Next-Generation Sequencing platform (Illumina MiSeq) was used on the bacterial DNA of the tuna steaks stored in ice (AIR – 0°C), vacuum (VP – 4/8°C) and modified atmosphere packaging (MAP – 4/8°C) until their respective sensory rejection point. At these dates, several bacterial strains were isolated and then inoculated in sterile tuna flesh to characterize their spoiling potential (challenge test). The organoleptic rejection of AIR products was observed at day 13 when total bacterial counts equaled 106 - 107 cfu.g-1. No extension of shelf-life was provided by VP and MAP. According to the metagenomic analysis, Rhodanobacter terrae was the main species of the freshly caught tuna. At the sensory rejection time, Brochothrix thermosphacta and Pseudomonas spp. dominated the AIR samples while B. thermosphacta alone or a mix of B. thermosphacta, Enterobacteriaceae and lactic acid bacteria dominated the microbiota of MAP and VP products, respectively. Pseudomonas spp., Enterobacter spp. and Escherichia spp. were categorized as non- or lightly-spoiling bacteria by the sensory panel; B. thermosphacta and Carnobacterium spp. exhibited moderate effects and were characterized by butter/caramel odors; Hafnia paralvei and Serratia spp. were considered as strong spoilers with pyrrolidine-like odors. When species were co-inoculated (by pair), the association between B. thermosphacta and Carnobacterium spp. favored a stronger deterioration while the addition of Pseudomonas spp. or B. thermosphacta to H. paralvei inhibited the developpement of unpleasant odors.