PhD Defence by Lorenzo Chinellato

Principal supervisor:

• Senior Scientist Claus Heiner Bang-Berthelsen

Co-supervisor:

• Professor Lisbeth Truelstrup Hansen
• Associate Professor, Nina Gringer

Examiners:

• Professor Charlotte Jacobsen, DTU Food
• Professor Eva Holmquist Falch, NTNU
• Industrial PhD, Senior Product & Process Developer Niels Bøknæs, Royal Greenland A/S

Moderator at defence:

• Associate Professor Susan Løvstad Holdt

Resume
As the Danish population of the European green crab (Carcinus maenas) is believed to have expanded in recent years, this species may have the potential to become a valuable and sustainable resource for small coastal fisheries. The low economic value of the green crab and high costs associated with its storage and distribution have thus limited its exploitation. As a results, it is often considered a by-catch and simply discarded at sea. Identifying novel strategies to valorise this resource while reducing costs associated with storage and distribution may be key to expanding its applications and supporting its applications in food and feed.

Although the green crab is so widely distributed, relatively few studies have comprehensively characterized the nutrient composition of this species, while even less is known about its microbiota. The lack of information severely constrains the potential development of new products let alone the formulation of preservation strategies tailored to this product.

Therefore, in this study we characterized the nutrient composition of the green crab, exploring how environmental seasonal changes and the alteration in catch composition may affect the nutrient content. The evidence we collected after a year of samplings pointed at a clear pattern as the shifts in sea water temperature promoted changes in dry matter, protein, fat and NaCl concentrations. To a lesser extent the presence of males in the catch was also correlated with a reduction of dry matter and protein. Among the monitored months, May-2023 produced the highest biomass and exhibited the best nutrient composition.

In the subsequent study we focussed on the characterization of the microbial communities associated with the green crab. Culture dependent and 16s rRNA sequencing methods were used to map the microbial succession throughout four sampling seasons, with particular emphasis on the occurrence of pathogenic and spoilage bacteria. The collected data described a clear influence of the season on the microbiota, with Vibrionaceae becoming dominant during January to April, and increasing in biodiversity from August to October. Among the screened pathogens B. cereus was detected.

The concluding work of this thesis, based on the gathered knowledge allowed us to propose a salting and fermentation method to extend the storage period of the crabs. The application of 15% NaCl in combination with a strain of T. halophilus displayed positive results, drastically altering the microbial community composition and preserving the protein content for a period of a month.

While method may not represent a definite solution for the preservation of green crabs, we hope that the knowledge gathered may guide future research to develop innovative preservation strategies and create new opportunities for the valorisation of this resource.

A copy of the PhD thesis is available for reading at the department