NMR Profiling Reveals Phenolic-Related Metabolite Motifs in the Most DPPH-Active Fraction of Scaevola taccada Young Leaves

Abstrak

Graphical Abstract Highlight Research: 1. Young leaves of Scaevola taccada are characterized for the first time as a fleshy, moisture- and mineral-rich, low-fat coastal biomass dominated by carbohydrates. 2. Extract recovery increased across the sequential fractions, and the ethanol fraction gave the highest yield (2.62%). 3. The ethanol fraction contained the widest range of metabolite classes and showed the strongest DPPH radical scavenging activity (IC50 = 416.40 ppm). 4. Integrated 1D/2D NMR profiling, to our knowledge applied to this species for the first time, detected catechol flavonoid and galloyl tannin signals that may contribute to the observed DPPH activity. Abstract Coastal halophytes remain undercharacterized sources of plant metabolites, particularly regarding the chemical composition and antioxidant properties of young Scaevola taccada leaves. This study integrated proximate composition, phytochemical screening, DPPH radical-scavenging activity, and NMR profiling of young leaves collected from Trikora Beach, Bintan Island, Indonesia. Three independent batches underwent fixed-order sequential extraction with n-hexane, ethyl acetate, and ethanol; the resulting fractions were assessed phytochemically and by DPPH assay, while the ethanol fraction alone underwent 1D/2D NMR profiling. On a fresh-weight basis, leaves contained 66.84% moisture, 23.65% carbohydrate, 5.53% ash, 3.30% protein, and 0.68% fat. Ethanol yielded the largest extract fraction (2.62%) and the lowest observed DPPH IC₅₀ (416.40 ± 124.92 ppm), compared with ethyl acetate (598.83 ± 71.03 ppm) and n-hexane (>1,000 ppm; extrapolated). However, DPPH activity did not differ significantly between the ethanol and ethyl acetate fractions, and all fractions showed weak activity relative to ascorbic acid. The ethanol fraction also contained the broadest range of qualitatively detected metabolite classes. NMR signals from this crude fraction were consistent with quercetin/luteolin-like flavonoid and galloyl/catechin-type tannin motifs, alongside sterol, triterpene, and glycoside-related signals. Because solvents were applied successively to the same leaf material, observed differences represent sequential fractions rather than independent effects attributable to solvent polarity considered alone. Together, these findings establish an integrated chemical baseline and suggest that phenolic-related constituents may contribute to the observed DPPH response, without identifying individual active compounds or demonstrating their contributions directly. Targeted fractionation, purification, and complementary LC-MS analysis are needed for compound-level identification and quantification.

Kata kunci

• Scaevola taccada
• Phenolic metabolites
• DPPH radical scavenging
• NMR profiling
• Sequential extraction