Antioxidant Capacity of Wolffia Protein Extracts Produced via UltrasoundAssisted Alkaline Extraction

This study aimed to investigate the antioxidant capacity of proteins extracted from Wolffia
arrhiza using ultrasound-assisted alkaline extraction (UAAE). The duckweed protein extract
(DPE) was obtained through a process of mixing rehydrated duckweed powder with a pH 8.5
aqueous solution at a weight ratio of 1:6. Ultrasound energy at an intensity of 107 W/cm² was
applied to disrupt cells, followed by 2-hour stirring and protein precipitation at pH 4.2. The
resulting DPE was analyzed for its chemical composition, total contents of amino acids
(TAAC), phenolics (TPC), and flavonoids (TFC). The antioxidant activities of the DPE were
evaluated using two different extracting solvents: pH 9.0 aqueous buffer and 95% (v/v) ethanol.
The results showed that the DPE contained 64.2±0.2% protein and 506.5 mg/gdry sample total
amino acids (TAA), with the essential amino acids (EAA) comprising 46.3% of the TAA. The
top three EAAs in the DPE were Leu, Phe, and Lys. Furthermore, the DPE was proved to
contain EAAs with an amount comparable to the FAO/WHO recommended protein intake for
preschool-aged children. The TFC in the DPE increased from 47.5±1.0 in native duckweed to
58.4 ± 2.8 mg.RE/g.sample, while the TPC decreased from 9.5 ± 0.5 to 8.0 ± 0.1
mg.GAE/g.sample (p<0.05). The antioxidant capacity of the DPE’s aqueous extract was
54.3 ± 0.3, in terms of ABTS, while that of the DPE’s ethanol extract was 15.1 ± 0.3
μM.TE/g.sample. In terms of FRAP, the activity of the aqueous extract was 85.8±1.5, while
that of the ethanol extract was 53.9±1.9 μM.TE/g.sample. The results indicated that the DPE’s
antioxidant capacity was associated with both water- soluble and insoluble compounds, in
which the antioxidant activities determined in aqueous extract were higher than those obtained
from ethanol extract. According to the analysis, DPE’s aqueous extract was mainly composed
of 70.0±2.3% proteins (dry weight basis), it might be possible that the DPE antioxidant capacity
in aqueous extract was primarily associated with the protein component. The DPE produced
may have significant implications in the future development of functional foods and feed.