Chemical composition and in vitro digestibility of duckweed (Wolffia globosa) and its polysaccharide and protein fractions

• Duckweed contains high levels of proteins and polysaccharides. • Ultrasound-assisted extraction could yield high protein and essential amino acids. • Duckweed polysaccharides were obtained through high pressure-assisted extraction. • Duckweed and its extracts exhibit low digestibility. Duckweed is considered a promising plant-based ingredient for future foods. In this study, duckweed polysaccharide (DPS) and protein (DPT) were extracted and characterized for their compositions and digestibility compared to the parent duckweed ( Wolffia globosa ) powder (DWP). DPS mainly consisted of carbohydrates (55 %w/w), followed by proteins (17 %w/w) and phenolic compounds (11 %w/w). While DPT showed significantly higher proteins (66 %w/w) and phenolics (27 %w/w), but lower in carbohydrates (11 %w/w). From monosaccharide analysis of DPS, galactose (72 % mol), glucose (22 % mol), and arabinose (7 % mol) were detected, implying the presence of arabinogalactan and starch. The presence of starch led to significantly higher digestibility of DPS in the oral phase compared to the gastric and intestine phases in the simulated gastrointestinal (GI) tract. Changes in molecular weight profiles were also observed after digestion, but its degree of hydrolysis indicating the digestibility was low. For DPT, aspartate, glutamate, and leucine were major amino acids. It exhibited low digestibility with the degree of hydrolysis comparable to that of DWP. The FT-IR spectra revealed that the main functional groups of polysaccharides and proteins were present in both extracts. Overall, Wolffia polysaccharide and protein extracts resisted digestion in the GI tract and should be further investigated their prebiotic potentials for improving gut health.