Protein extraction from duckweed ( Lemna minor ): effects of extraction method and calcium chloride treatment on colour reduction and functional properties

Abstract Duckweed (Lemna spp.) is a globally distributed aquatic plant with strong potential as a human protein source and has European Union novel food authorisation as powder and whole plant material. This study evaluates innovative extraction approaches, including ultrasound-assisted extraction (UAE), and compares pigment reduction and protein functionality with conventional methods. The addition of CaCl₂·2H₂O effectively removed green pigments, yielding a light-beige protein concentrate with the highest protein purity, but significantly reduced protein yield. In contrast, UAE combined with ultrafiltration without CaCl₂ achieved the highest protein yield (43.29%) but retained the most chlorophyll, producing a dark-green concentrate. All protein concentrates met or exceeded Food and Agriculture Organization essential amino acid (AA) requirements, with no limiting AAs for children or adults. Lysine was the lowest-scoring AA, while ultrasound reduced histidine content. The nitrogen conversion factor was ~5.8. Sodium dodecyl sulphate–polyacrylamide gel electrophoresis identified RuBisCo subunits (55 and 14 kDa) and LHCB1. The absence of detectable bands in CaCl₂-treated and 10 kDa ultrafiltrated samples suggests higher hydrolysis. The highest protein solubility (~85%) and foaming capacity were achieved with UAE, CaCl₂, and ultrafiltration, though foam and emulsion stability decreased, while emulsion capacity remained comparable to Lemna minor (LM)-C and egg white.