In Vitro Phytochemical Profiling and Evaluation of the Antioxidant and Antibacterial Potential of Rhododendron Flower Extracts from the Hilly Region of Nepal
Year: 2026
Type: preprint
Abstract: Objectives: Rhododendron species are widely used in Himalayan traditional medicine, but the phytochemical composition, antioxidant capacity, and antibacterial potential of their flower, particularly against clinically relevant gram-negative bacteria, remain poorly characterized for Nepalese populations. This study aims to evaluate the phytochemical profile of total phenolic/flavonoid content, antioxidant activity, and antibacterial potential of sequential solvent extract of Rhododendron flowers collected from two sites in Nepal. Materials and Methods: Dried flowers from two sites, R1 and R2, were sequentially extracted with hexane, ethyl acetate, methanol, and water. Extracts were screened quantitatively for major phytochemical classes and total phenolic content (TPC) and total flavonoid content (TFC) were determined colorimetrically. Antioxidant activity was assessed by DP-Ph and ABTS radical scavenging assay. Antibacterial activity of the methanol and ethyl acetate extracts was evaluated against Escherichia coli, Klebsiella sp., and Pseudomonas sp. by agar well diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) assays. Results: Methanol gave the highest extraction yield (17-18%) and the richest phytochemical profile, particularly flavonoids and tannins. TPC and TFC were highest in methanol extracts (up to 78.4 mg GAE/g and 46.2 mg QE/g, respectively) and were significantly negatively correlated with DPPH IC50 (r = −0.75 to −0.79, p < 0.05). Methanol and ethyl acetate extracts showed the strongest antioxidant activity (IC50 as low as 18.2 µg/mL), while hexane extracts were the weakest in both assays. The ethyl acetate extract of R2 and the methanol extract of R1 showed the strongest antibacterial activity, with the lowest MIC (12.5 mg/mL) recorded against E. coli, and predominantly bactericidal action (MBC/MIC ≤ 4) against all three bacterial genera. Conclusion: Rhododendron flower extracts, particularly the methanol and ethyl acetate fractions, are rich in phenolic and flavonoid compounds and exhibit notable antioxidant and antibacterial activities, supporting their potential as natural sources of bioactive compounds against oxidative stress and antimicrobial-resistant pathogens.
Source: Preprints.org
Language: English
Subfield: Food Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7204194128