Biotechnological approaches to enhance nutrient bio-accessibility from algal biomasses: A comparative study of enzymatic hydrolysis and microbial fermentation

Enhancing nutrient bio-accessibility from algal biomasses is essential for maximizing their potential in fish nutrition and health applications. This study evaluates the protein bio-accessibility of a blend of algae composed of several species (Arthrospira sp., Chlorella sp., Microchloropsis sp., Tisochrysis sp., and Ulva sp.) as potential functional ingredient for Chelon labrosus. Different biotechnological treatments, including enzymatic hydrolysis, microbial fermentation, and a combination of both, were applied to improve the availability of key algal compounds. All treatments led to a significant increase in the release of reducing sugars, amino acids, polyphenols, and soluble proteins compared to the untreated algal blend. Cytotoxicity was also evaluated to ensure the safety of each processed algae blend. In the final stage, an in vitro digestive simulation assay using C. labrosus intestinal enzymes was conducted to assess the bio-accessibility of proteins, carbohydrates, and polyphenols from both untreated and treated algae. Results indicated that the sequential biotechnological treatment –consisting of an enzymatic hydrolysis followed by a microbial fermentation– was the most effective in enhancing the availability of valuable nutrients such as reducing sugars, amino acids, and polyphenols. This sequential approach significantly improved nutrient bio-accessibility, making it a promising strategy for aquafeed formulations. The study provides a basis for the development of nutritionally optimized, algae-based ingredients for aquaculture feeds, especially for species like mullets, which have specific digestive enzyme profile.