In humans, many diseases are associated with the accumulation of free radicals. Antioxidants can scavenge free radicals and minimize their impact. Therefore, the search for naturally occurring antioxidants of plant origin is imperative. Here, we aimed to investigate the antioxidant and free radical scavenging properties of methanolic extracts from Tabebuia pallida (T. pallida) stem bark (TPSB), root bark (TPRB), leaves (TPL), and flowers (TPF). The antioxidant and free radical scavenging activity were determined by several standard methods using spectrophotomer. Total phenolic and flavonoid contents were estimated using Folin-Ciocalteu reagent and aluminum chloride colorimetric assay methods, respectively. Among the extracts, TPL showed the highest total antioxidant capacity followed by TPRB, TPF, and TPSB. Based on DPPH and hydroxyl radical scavenging activity, TPL showed strong scavenging activity (91.05 ± 1.10 and 62.00 ± 0.57) with IC50 of 9.20 ± 0.28 and 46.00 ± 2.84 μg/mL, respectively when compared with standard BHT (IC50 of 7.00 ± 0.25 μg/mL) and CA (75.00 ± 0.14 μg/mL). These results suggest that TPL had the highest radical scavenging activity among the extractives that closely resembled the standard’s. In lipid peroxidation inhibition assay, TPL exhibited the most potent inhibitory activity (83.18 ± 2.12 %) with IC50 of 12.00 ± 2.12 μg/mL, which closely resembled standard CA (IC50 of 10.50 ± 0.28 μg/mL). Also, the reducing capacity on ferrous ion was in the following order: TPL > TPRB > TF > TPSB. The phenolic and flavonoid contents of TPL were higher than other extractives. A positive correlation (p value <0.001) was observed between phenolic content and free radical (DPPH· and ·OH) scavenging efficiencies and lipid peroxidation inhibition activity. Methanolic extract of T. pallida leaf is a potential source of natural antioxidants and serves as an effective free radical scavenger and/or inhibitor. Hence, T. pallida might be a good plant-based pharmaceutical product for several diseases caused by free radicals.

Aim: Tiliacora triandra (T. triandra), a species of Menispermaceae family, has folkloric reputation for the treatment of several diseases including infectious diseases in Thailand and neighboring countries. The present study aimed at screening the stem bark of T. triandra for its phytochemical constituents and its antimicrobial potential against selected bacteria and fungi. Materials and Methods: The dried stem bark of T. triandra was extracted with methanol and qualitative phytochemical analysis was performed. The antimicrobial activity was determined by disc diffusion assay method against some bacteria and fungi. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by serial dilution method to establish the antimicrobial potential of the extract. Results: Qualitative phytochemical analysis revealed the presence of phenolics, flavonoids, terpenoids, alkaloids, saponins and cardiac glycosides. Susceptibility testing by disc diffusion assay showed significant antimicrobial activity against the tested pathogens. The highest antibacterial activity was observed against a Gram-negative bacterium Escherichia coli (E. coli) where the zones of inhibition were 15 mm and 21 mm at the potencies of 250 and 500 µg/disc, respectively. The stem bark extract also showed moderate activity against Shigella sonnei (14 mm), Shigella dysenteriae (13 mm), Agrobacterium spp (13 mm) bacteria and fungus, Aspergillus niger (14 mm) at 250 µg/disc. The results also revealed equal MIC and MBC values of 62.5ug/mL against E. coli. Conclusions: Our findings revealed that the methanol extract of T. triandra possesses potent antimicrobial activity which may be attributed to the identified phytochemical components of the plant extract.