Effect of enzymatic saccharification on edible seaweed (Ulva sp.) fermentation

Edible seaweeds are a promising substrate for microbial fermentations and the development of novel food products. However, the unique composition of their cell wall can limit microbial growth. To address this, the edible seaweed Ulva sp. was subjected to enzymatic saccharification using: (i) a crude extract of Aspergillus oryzae grown on Ulva sp.; (ii) a commercial enzymatic cocktail; and (iii) a combination of both. Saccharification with the latter substantially increased the release of fermentable sugars, with glucose (157.08 mg/g_substrate) and galacturonic acid (153.83 mg/g_substrate) as the dominant products, indicating disruption of key structural polysaccharides. Follow-up fermentations with Lactiplantibacillus plantarum and Cyberlindnera jadinii (GRAS microorganisms) exhibited a two-log growth increase compared to cultures in non-saccharified media. Saccharification also led to increased acidification and free amino nitrogen release by L. plantarum, and an increased nitrogen intake by C. jadinii, changes directly relevant to food fermentations. Despite these advances, the limited release of certain sugars suggests that some cell wall components remain resistant to hydrolysis. Overall, this work highlights enzymatic saccharification as a key enabling step for converting Ulva sp. into a viable and functional substrate for microbial fermentation and novel food development. KEY POINTS: • A. oryzae extract combined with cellulolytic enzymes led to highest sugar yield. • Saccharification improved growth, FAN release, and acidification by L. plantarum. • Evidence of cellulose hydrolysis but not of the remaining cell wall polysaccharides.