Optimizing ultrasonic-assisted extraction and untargeted metabolite identification from red water lily (Nymphaea rubra) leaves with enhanced antioxidant activity

Abstract

This study aimed to optimize the ultrasonic-assisted extraction of polyphenolic compounds from red water lily (Nymphaea rubra) leaves (NRL) with heightened antioxidant activities and perform untargeted metabolite identification. Response surface methodology, employing Box-Behnken design, determined optimal conditions: 53.0 % ethanol, 32.0 min extraction time, and 53.0 °C temperature. The resulting extraction demonstrated significant total phenolic content of 45.12 ± 1.12 mgGAE/g and total flavonoid content of 44.05 ± 1.65 mgCAE/g. High-resolution mass spectrometry identified 150 secondary metabolites, encompassing phenols, flavonoids, tannins, terpenoids, and fatty acids. The optimized NRL extract exhibited notably increased radical scavenging abilities (19.21 ± 1.71 μM ASCE/g for DPPH and 24.59 ± 1.35 μM ASCE/g for ABTS) along with elevated reducing power potential (63.35 ± 4.28 μM ASCE/g for CUPRAC and 61.32 ± 2.56 μM ASCE/g for FRAP) in comparison to traditional extracts, which ranged from (7.23 ± 1.58 to 15.13 ± 1.79 μM ASCE/g, 13.29 ± 1.32 to 19.29 ± 1.69 μM ASCE/g, 22.74 ± 1.68 to 54.37 ± 3.38 μM ASCE/g, 24.14 ± 2.00 to 52.77 ± 2.33 μM ASCE/g for DPPH, ABTS, CUPRAC and FRAP, respectively). This suggests its promising potential for incorporation into antioxidant-rich functional foods. These findings underscore NRL's promise for commercial applications in the nutraceutical, food, and pharmaceutical industries.