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PhD defense of Norman Wiernascz

2 avril 2019 - Oniris, Site de la Chantrerie

PhD defense of Norman Wiernascz
On the topic: Seafood quality and safety improvement through hurdle technology, including biopreservation. Impact on microbial ecosystems.

PhD thesis:

Supervised by Marie-France Pilet (SECALIM) and co-supervised by Françoise Leroi (IFREMER)

As part of the European project SAFEFISH DISH


Seafood products count for an important part of our diet. However, they are fragile and have a limited shelf-life due to microbial spoilage. The objective of this thesis was to develop a biopreservation strategy applied to a salmon-based product, the gravlax, in order to improve its microbiological quality and safety. We firstly characterized this poorly known product on a microbiological (cultural analysis and metabarcoding of the 16S rRNA encoding gene), physico-chemical (biogenic amines and volatile organic compounds...) and sensorial point of view. Compared to smoked salmon packed under vacuum or modified atmosphere, the gravlax shows a higher microbial diversity, dominated by enterobacteria and linked to a specific volatilome and sensory profile. In a second time, six lactic acid bacteria strains were selected on technological criteria such as antimicrobial activity, spoilage potential, tolerance to freezing and chitosan, as well as safety criteria such as biogenic amines production and antibiotic resistance. These 6 strains were then applied on gravlax to evaluate their bioprotective potential. They are distinguished by their implantation capacity and their impact on the product microbial ecosystem, volatilome and sensory properties. A strain of Vagococcus fluvialis and Carnobacterium maltaromaticum were able respectively to control the sensorial spoilage and to inhibit Listeria monocytogenes, during gravlax refrigerated storage.


biopreservation, metabarcoding, microbial ecosystem, volatilome, sensory analysis, gravlax


Lisbeth Truelstrup Hansen (DTU, Denmark)

Luca Cocolin (UNITO, Italy)

Stéphane Chailloux (Micalis, INRA France)

Jean-Michel Cappelier (SECALIM)