PhD Defence by Caroline Østergaard Klein

Principal supervisor:

• Professor Lisbeth Truelstrup Hansen

Co-supervisors:

• Associate Professor Susan Løvstad Holdt
• Senior Scientist Claus Heiner Bang-Berthelsen
• Niels Bøknæs, PhD, Royal Greenland A/S

Examiners:

• Associate Professor Anurag Kumar Sinha, DTU Food
• Professor Mieke Uyttendaele, Ghent University, Belgium
• Professor Turid Rustad, Norwegian University of Science and Technology, Norway

Moderator at defence:

• Senior Scientist Tina Beck Hansen

Resume
Seaweed cultivation is emerging in Europe. To ensure optimal quality, seaweed is harvested once a year over a few weeks in late spring and early summer. Once harvested, seaweed has a short, refrigerated shelf-life of a week if not immediately treated. Commonly, freezing or drying are used as post-harvest treatments, but they are energy-intensive and require specialised facilities. Therefore, there is a need to investigate simple, low-energy-intensive post-harvest treatments to preserve seaweed and make it available year-round for high-quality and safe food products.

The overall aim of this PhD project was to establish sustainable post-harvest treatments for brown seaweed (kelp) and processing methods for kelp-based products.

The research focused on the food safety and quality of kelp after simple post-harvest treatments such as salt-pickling and acid brining, of two kelp species: sugar kelp (Saccharina latissima) and winged kelp (Alaria esculenta). The studies demonstrated that it is possible to extend the shelf-life of kelp from a week to more than 500 days when treating kelp with ≥20% NaCl (salt-pickling) or acid brining with NaCl, acetic acid, and sorbic acid. The kelp was preserved with regard to microbial quality, had no off-odour and remained brown in colour. This work made kelp available year-round, even beyond the next harvest, for use in food products.

The preserved kelp products were used in ready-to-eat seaweed salads without or with an acidic dressing. Seaweed salads were developed with previously frozen raw or blanched kelp, or acid brined kelp followed by storage without or with an acidic dressing. In the case of blanched kelp, the growth of the food-borne pathogens, Bacillus cereus and Listeria monocytogenes, was supported. However, growth was inhibited in salads prepared with raw and acid brined kelp. Mixing kelp with an acetic dressing also inhibited the growth.

This work demonstrated how simple, low-energy-intensive post-harvest treatments can transform kelp into a safe, stable product with industrial applicability. The treatments enable year-round utilisation of kelp as a food ingredient and facilitate the development of a sustainable European kelp industry.

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