The biochemical composition of the seagrass Halodule pinifolia collected from Pasiagan, Bongao, Tawi-Tawi, Philippines was investigated to assess its potential nutraceutical and pharmacological applications. Phytochemical screening revealed the presence of alkaloids, tannins, flavonoids, phenolics, saponins, steroids, and triterpenoids. Proximate analysis demonstrated considerable nutritional value, with protein (12.46%), carbohydrates (52.82%), lipids (0.85%), and ash (33.87%), with the high ash content suggesting substantial mineral content. Cytotoxicity assessment yielded an LC₅₀ of 867.32±0.028 µg mL-1 (mean±SD), indicating low cytotoxicity. Quantitative analyses showed a total phenolic content (TPC) of 0.869±0. 014 mg GAE g-1 and a total flavonoid content (TFC) of 0.34±0.091 mg QE g-1. Antioxidant assays demonstrated free-radical-scavenging activity in both DPPH (0.725±0.021 mg Trolox g-1) and ABTS (0.196±0.017 mg Trolox g-1) systems. These findings indicate that H. pinifolia contains nutritionally relevant constituents and phytochemicals associated with antioxidant activity. The species, therefore, warrants further investigation as an underexplored marine resource for potential functional food and nutraceutical applications.
