Protein Extraction from Duckweed ( Lemna minor ): Effects of Extraction Method and Calcium Chloride Treatment on Colour Reduction and Functional Properties

Duckweed (Lemna spp.) is a globally distributed aquatic plant with strong potential as a human protein source and has EU novel food authorization 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 FAO essential amino acid requirements, with no limiting amino acids for children or adults. Lysine was the lowest-scoring amino acid, while ultrasound reduced histidine content. The nitrogen conversion factor was ~5.8. SDS-PAGE 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 LM-C and egg white.