Preliminary Phytochemical Screening and In Vitro Antioxidant Activity of Ocimum sanctum (Tulsi) Leaf Extract: A Laboratory-Based Study

Abstract

Background: Oxidative stress, driven by an imbalance between reactive oxygen species and endogenous antioxidant defences, contributes to the pathogenesis of numerous chronic and degenerative disorders. Medicinal plants remain an important, low-cost source of natural antioxidants, and Ocimum sanctum Linn. (Tulsi, holy basil) occupies a revered place in the traditional medicine of South India.
Objective: To perform a preliminary qualitative phytochemical screening and to evaluate the in vitro free-radical-scavenging capacity of a hydroalcoholic leaf extract of Ocimum sanctum, and to relate its antioxidant activity to its phenolic and flavonoid content.
Methods: This was an experimental in vitro laboratory study conducted on a hydroalcoholic (ethanol–water) leaf extract of O. sanctum. Fifteen extract batches were prepared and screened qualitatively for major phytochemical classes using standard tests. Antioxidant activity was assessed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay across concentrations of 10–100 µg/mL in triplicate, with the median inhibitory concentration (IC50) derived by linear regression. Total phenolic content (TPC) and total flavonoid content (TFC) were determined by the Folin–Ciocalteu and aluminium chloride colorimetric methods, respectively. Data are summarised as mean ± standard deviation.
Results: The mean extraction yield was 15.25 ± 2.48% (range 11.14–18.57%). Flavonoids, phenolics and terpenoids were detected in all 15 batches (100%), with alkaloids and carbohydrates (73.3%), saponins (66.7%), tannins (60.0%), glycosides (53.3%) and steroids (46.7%) present at lower frequencies; proteins were trace or absent. DPPH scavenging was concentration-dependent, rising from 8.90% at 10 µg/mL to 79.89% at 100 µg/mL (linear fit R² = 0.9985), yielding an extract IC50 of approximately 62.0 µg/mL. TPC was 99.89 ± 16.58 mg gallic acid equivalents (GAE)/g and TFC was 51.40 ± 9.81 mg quercetin equivalents (QE)/g.
Conclusion: The hydroalcoholic leaf extract of O. sanctum is rich in phenolics, flavonoids and terpenoids and exhibits moderate, concentration-dependent antioxidant activity consistent with its high phenolic and flavonoid content. These findings provide laboratory support for the traditional South Indian medicinal use of Tulsi and illustrate a simple, low-cost screening approach.