Qualitative and Quantitative Phytochemical Profiling of <i>Hibiscus sabdariffa</i> L. Seeds: Secondary Metabolite Characterization and Implications for Nutraceutical and Therapeutic Applications<b></b>

Hibiscus sabdariffa L. (Malvaceae), commonly known as roselle, is a widely cultivated multipurpose plant of considerable ethnopharmacological relevance across tropical and subtropical regions of Africa, Asia, and the Americas. Despite sustained global interest in the phytochemistry of its calyces and leaves, systematic characterisation of the seed fraction remains comparatively underexplored. This study reports a parallel qualitative and quantitative phytochemical analysis of methanolic extracts of H. sabdariffa seeds sourced from the Onigambari Research Station, Ibadan, Nigeria. Qualitative screening conducted according to Harborne (1973) and Evans (2009) detected seven of nine secondary metabolite classes tested. Alkaloids, terpenoids, and steroids were recorded as abundantly present (++), while flavonoids, saponins, cardiac glycosides, and anthraquinones were present (+). Tannins and free phenols were absent (−). Gravimetric quantification yielded alkaloids at 1.55 ± 0.002% (w/w), terpenoids at 1.30 ± 0.001% (w/w), and saponins at 0.45 ± 0.002% (w/w). Spectrophotometric analyses, performed in triplicate against validated calibration curves (R² ≥ 0.99), gave: total tannin content (TTC) of 1.05 ± 0.007% (w/w) gallic acid equivalents (GAE); total flavonoid content (TFC) of 0.28 ± 0.249% (w/w) quercetin equivalents (QE); and total phenolic content (TPC) of 0.83 ± 0.001% (w/w) GAE. The detected phytochemical assemblage is consistent with reported antioxidant, anti-inflammatory, antimicrobial, and cardioprotective activities of the species. These findings provide an empirical basis for the seed's continued evaluation as a nutraceutical ingredient and herbal medicine resource.