The development of a biorefinery strategy for the valorization of Ulva biomass

This work focused on the optimization of a biotechnological procedure to obtain high-added-value products from macroalga Ulva sp. biomass, ensuring full usage of the biomass with zero waste and obtaining an ulvan-rich aqueous fraction and a valorized “residual algal by-product" with enhanced nutrient bioavailability, suitable for use as a dietary ingredient.

Ulva biomass was subjected to a biotechnological process involving enzymatic hydrolysis using a combination of commercial enzymes (protease, xylanase, cellulase, and β-glucanase), followed by fermentation with Bacillus subtilis and Saccharomyces cerevisiae. The resulting biomass was centrifuged to obtain two products: (i) an ulvan-rich algal extract and (ii) a valorized “residual algal by-product”. To evaluate the effectiveness of the process, samples were withdrawn at different times for quantifying the release of reducing sugars, amino acids and total polyphenols. In addition, ulvan was extracted from the aqueous extract following a hot-water method, and the ulvan yield was calculated following the equation: Ulvan yield = [dry weight of ulvan obtained / dry weight of algal biomass] x100. The chemical composition of residual algal by-product was also evaluated using standardized procedures. The results confirmed the effectiveness of the biotechnological procedures to improve the nutritional quality and nutrient bioavailability, as evidenced by the significant increase in the release of amino acids and total polyphenols. Ulvan yield showed results exceeding 10%, confirming the effectiveness of the treatments tested. Moreover, the residual algal by-product showed significantly higher crude protein and total lipid content than the untreated biomass, resulting in an improved nutritional profile.

These findings not only corroborate the effectiveness of this biotechnological treatment to obtain bioactive compounds like ulvan but also highlight the potential of residual algal by-products as an alternative source of protein and lipids in formulated aquafeeds, which aligns with circular economy principles by minimizing waste generation.