Ultrasound-assisted alkaline extraction of proteins in several algae and their nutritional characteristics

Abstract

Ultrasound-assisted alkaline extraction (UAAE) and the nutritional quality of proteins from five algae (Arthrospira platensis, Cladophora glomerata, Porphyra tenera, Laminaria japonica and Undaria pinnatifida) were investigated. The UAAE of the A. platensis protein using a 60% amplitude level and 30 min extraction time provided the highest protein yield (81.86%) and altered the surface of A. platensis. Amino acid profiles revealed that lysine and branched-chain amino acids (BCAAs) were dominant in most algal proteins. The C. glomerata protein had the highest digestibility (94.09%) and protein digestibility-corrected amino acid scores for the BCAAs. The L. japonica protein demonstrated a rich source of aspartic and glutamic acids, giving an umami taste. The algal proteins contained low contents of carbohydrates (3.87–44.83 mg glucose equivalents g−1) and nucleic acids (0.60–8.57 mg g−1), while total phenolics were 6.13–70.13 mg gallic acid equivalents g−1. Algal proteins could be a good ingredient in developing vegan and vegetarian foods.