Protein extraction from the industrial solid residue of brown seaweed after alginate extraction

The growing interest in the “blue-bioeconomy” and the valorization of macroalgae has driven research and industrial efforts to develop valorization strategies for the by-products generated during alginate extraction. Sequential extraction methods, such as acid/alkali treatment, enzymatic, ultrasound, and pH-shift process, were investigated and compared in order to obtain protein extracts from the solid residues after alginate extraction from two brown seaweed species ( Ascophyllum nodosum and Saccharina latissima ). Applying a sequential extraction, combining several methods, allowed the recovery of more than 29.5 % of the total protein from the residues. The resulting extracts exhibited optimal functional properties in terms of oil and water retention and outstanding emulsifying and foaming capacity. In addition, the protein extracts showed considerable polyphenol content, remarkable antioxidant activity, and an enhanced ability to inhibit angiotensin-converting enzyme (ACE). This study demonstrated that the residues after alginate extraction are a sustainable and promising source of protein with potential applications in the food industry. • Solid residues after alginate extraction are a good source of protein. • Up to 75 % of protein was recovered by a sequential extraction process from residues. • The protein fraction in the extracts contains 43–50% of essential amino acids. • Composition, functional and bioactive properties were assessed.