Chemical Compositions and Antioxidant Activities of a Specialty Aquatic Vegetable Nymphoides hydrophylla in Taiwan

Abstract

Nymphoides hydrophylla (NH), a lesser known aquatic vegetable, is a popular dish among the Hakka community in Taiwan. This study aimed to examine the proximate and polyphenolic compositions of NH and evaluate its antioxidant activities using various antioxidant assays. Results showed that the moisture, crude protein, crude fat, carbohydrate (crude fiber), and ash contents of fresh NH were 89.46, 0.46, 0.47, 4.11 (3.65), and 5.50%, respectively. In the antioxidant studies, the NH ethanolic extract (NH-E) exhibited higher antioxidant activities than the aqueous extract (NH-H) in the antilipid peroxidation, reducing power, metal chelation, and 2,2ʹ-azino-bis(3-ethylbenthiazoline-6-sulfonic acid) or ABTS radical scavenging assays, while NH-H possessed more potent activity in the superoxide and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays. Compared with NH-H (6.86 mg/g for total flavonoids and 48.83 mg/g for total phenolics), NH-E showed a higher content of total flavonoids (197.21 mg/g) and total phenolics (79.43 mg/g). High-performance liquid chromatography (HPLC) analysis showed that the main difference between NH-H and NH-E polyphenolic contents was derived from the concentrations of kaempferol and quercetin.