Evaluation of the in vitro protein bioaccessibility of several microalgae and cyanobacteria as potential dietary ingredients in gilthead seabream (Sparus aurata) juveniles

This work addresses the evaluation in vitro of different marine (Dunaliella salina REC-0214B and Microchloropsis gaditana REC-0251B) and freshwater (Anabaena sp. BEA-0300B, Arthrospira platensis BEA-0007B, Chlorella vulgaris BEA-0753B, Spirogyra sp. BEA-0666B) microalgae and cyanobacteria as potential dietary ingredients in aquafeeds. For this purpose, total protein content, amino acid composition, and the presence of protease inhibitors were evaluated. In addition, protein bioaccessibility was estimated using a species-specific in vitro assay using Sparus aurata digestive enzymes. Overall, all the microalgae showed high protein content ranging from 25 to 61%, and a balanced essential to non-essential amino acid content (from 0.81 to 0.95). The inhibition assay confirmed the absence of protease inhibitors whatever the microalgae considered. Finally, the in vitro assays showed differences in the degree of protein hydrolysis with values for the coefficient of protein degradation ranging from 49.4% in Spirogyra sp. to 85.5% in D. salina. Similarly, the total amount of free amino acids released from the microalgal biomass (from 12.8 to 20.8 g L-leucine equivalents (100 g protein)−1), as well as their qualitative amino acids profile varied among the different species, although the profile can be considered as well balanced in all cases. In conclusion, the results obtained revealed that, even if significant differences were observed among species in terms of their susceptibility to be hydrolysed by S. aurata digestive enzymes, all the microalgae and cyanobacteria evaluated presented an adequate protein content and a balanced amino acid profile.