Abstract/Summary

Edible seaweeds represent a promising but underutilized food resource, limited by challenges such as poor consumer acceptance, high perishability and a complex cell wall that hinders their fermentability. This thesis explored biotechnological strategies to characterise and enhance the fermentability of three edible seaweeds, namely Fucus vesiculosus, Porphyra dioica, and Ulva sp., through microbial fermentation and enzymatic saccharification. Three food-grade microorganisms, namely Cyberlindnera jadinii, Lactiplantibacillus plantarum, and Aspergillus oryzae, were assessed for their ability to ferment seaweed substrates. Results demonstrated that microbial growth and metabolite production were closely tied to the availability of soluble sugars and free amino nitrogen within seaweed substrates. F. vesiculosus yielded the highest amount of soluble monosaccharides (97.6 ± 6.3 mg/g) and led to the highest viable colony counts in for both L. plantarum (6.3 × 109 CFU/mL) and C. jadinii (2.6 × 108 CFU/mL). The latter demonstrated a strong capacity to influence the volatile profile of seaweeds by reducing undesirable aroma compounds such as hexanal and (Z)-4-heptenal, and introducing fermentation-derived volatiles, including 3-methyl-1-butanol and phenylethyl alcohol, with the potential to improve overall sensory appeal. The enzymatic saccharification of Ulva sp. using a combination of A. oryzae-derived and commercial enzymes significantly increased fermentable sugar availability, up to a maximum glucose yield of 157.1 ± 1.1 mg/g. This led to an increase in maximum viable colony counts of L. plantarum and C. jadinii, as well as enhanced lactic acid production in the former and volatile profile development in the latter. Additionally, the saccharification potential of purple sea urchin (Paracentrotus lividus) gut extracts was investigated, revealing their capacity to hydrolyse complex seaweed polysaccharides into assimilable sugars. This effect was most significant in Ulva sp., where glucose concentrations raised from below detection limit to a maximum of 178.64 ± 2.0 mg/g after exposure to the gut extracts. The findings of this thesis provide solid evidence on the potential of fermentation as a tool to improve the nutritional attributes of edible seaweeds, particularly when combined with targeted enzymatic pre-treatment. Moreover, by addressing technical and sensory limitations of seaweed fermentation, this research generated novel information and laid foundations for the broader adoption of seaweeds as a viable and innovative food resource in the global market.