Impact of structure and composition on the digestibility and nutritional quality of alternative protein-rich extracts from the green seaweed Ulva lacinulata

This study reports on the nutritional quality of protein-polysaccharide extracts obtained from the green seaweed Ulva lacinulata, through a previously optimized method, evaluating the impact of their distinct composition and structure. Protein solubility was strongly influenced by protein-polysaccharide interactions, being higher in extracts with lower polysaccharide content. This, in turn, had a significant impact on the in vitro protein digestibility. In particular, protein digestibility was found to be higher in those extracts with higher protein content, reaching approximately 62-75 %, hence largely improving the digestibility of the native seaweed (ca. 25 %). The protein nutritional quality in the native seaweed was relatively poor, as suggested by the low Digestible Indispensable Amino Acid Score (DIAAS) (ca. 18 for adults), with histidine being the limiting amino acid. On the other hand, the extracts showed significantly greater DIAAS values, especially in those with lower polysaccharide content (up to 31), with lysine being the limiting amino acid. These findings provide the basis for the design of seaweed-based protein-rich ingredients with enhanced protein digestibility and nutritional quality, for their implementation in the food industry.