Effects of alkaline extraction and ultrasonication on digestibility, nutritional quality, and bioactive peptide release of duckweed (Wolffia arrhiza) protein extracts

Duckweed is a promising sustainable protein source; however, its dense structure and anti-nutritional factors (e.g., saponins and tannins) may limit protein digestibility, nutritional, and biofunctional qualities. This study compared duckweed protein extracts (DPE) produced by alkaline extraction (AE), ultrasound-assisted alkaline extraction (UAAE), and ultrasound-assisted water extraction (UAWE) to native duckweed powder (DPw) regarding protein digestibility, antioxidant capacity, and bioactive peptide (BAP) release during in vitro gastrointestinal digestion. DPw exhibited the lowest digestibility, whereas DPE UAE showed the highest, with UAWE achieving a DIAAS of 0.75, meeting FAO criteria for good protein quality. Enhanced digestibility strongly correlated with increased BAP release; DPE UAE boosted long-chain BAPs by 1.4-fold and short-chain BAPs by 1.8-fold versus DPw, without altering bioactivity distribution. Furthermore, DPE UAE demonstrated superior antioxidant capacity, with ACE and DPP-4 inhibitory activities as the top-two predominant bioactivities. UAE effectively produces DPE, demonstrating potential as a functional protein ingredient for food and dietary supplement applications.