Investigations of the Palestinian medicinal plant basil (Ocimum basilicum): antioxidant, antimicrobial activities, and their phase behavior

Abstract

Objective: The aim of this work was to establish pseudoternary phase diagrams for Palestinian basil extracts (seeds and leaves), formulate a microemulsion, and study the antioxidant and antimicrobial effects of this medicinal plant. Methods: Pseudoternary phase diagrams were prepared by utilizing the water titration method, by using basil extracts (seeds and leaves) as an oil phase and water phase. Basil was analyzed for its phytochemical constituents after it was extracted using Soxhlet extraction device. The crude extracts of basil (seeds and leaves) were analyzed for their total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (AA) using standard methods (Folin-Ciocalteau assay, aluminum chloride assay, ferric reducing/antioxidant power (FRAP) and spectrophotometric method), respectively. In-vitro susceptibility of basil extracts was determined by antibacterial activity using agar disc diffusion method, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) against five clinical pathogens. The potential in-vitro antimalarial activity of various Ocimum extracts was determined in different solvents using semiquantitative assay method. Results: The results showed that both the seeds and leaves of the ethanol extract had antibacterial activity on most bacterial strains, with respective zones of inhibition of 6-25 mm and MIC values of (62.5 - > 500μg/ml). The seeds extract of the plant has 74±1.4 mg/g AA, while the leaves extract has a value of 40.4±0.8 mg/g. The TPC of basil seeds was 58.2±0.9 mg/g and that of basil leaves was 51±2.4 mg/g. In addition, the TFC in the leaves was 9.0±1.5 mg/g, while in the seeds it was 34.2±3.6 mg/g. At room temperature, the pseudoternary phase diagram was determined. Combining basil leaves and seeds extract with Tween 20 as a surfactant resulted in an effective basil microemulsion. RP-HPLC Chromatography analysis showed the presence of flavonoid (quercetin) in 6.6 min. It was found that β-hematin was not prevented in any of these solvents. This result, shown for the first time in this study, rules out a mechanism that has been proposed to explain the antimalarial activity of the plant, namely inhibition of beta-hematin formation. Conclusion: Based on these results, it is concluded that basil is a natural source of potent antioxidants, antibacterial and antimalarial activities that can prevent many diseases and could potentially be used in cosmetics and pharmaceutical products.