Evaluation of total phenolic content and antioxidant activity of Tabernaemontana dichotoma

Abstract

Sri Lanka is recognized as a global biodiversity hotspot, which possesses a diverse range of fruits, yet a significant portion of them is underutilized. Numerous phytochemicals found within plants have a wide variety of medicinal applications including acting as antioxidants. Phenolic compounds are excellent oxygen radical scavengers, because the electron reduction potential of phenolic radicals is lower than the electron reduction potential of oxygen radicals. Therefore, the objective of this study was to evaluate the total phenolic content and the antioxidant activity of Tabernaemontana dichotoma, a plant species commonly known as “Divi kaduru” or “Eve’s apple” collected from Gampaha district, Sri Lanka. This plant was chosen for this research because it was easily found, frequently used in traditional medicine, and has not been researched before. Crude extracts of the fruit and seed of T. dichotoma were prepared by sequential extraction using hexane, ethyl acetate and methanol at room temperature for 48 hours for each solvent respectively. Spectrophotometric technique using Folin - Ciocalteu reagent was performed to evaluate the total phenolic content of the extracts and results were expressed as Gallic acid equivalents (GAE) per gram of dry weight of the sample. Then the 2,2- diphenyl-1- picrylhydrazyl (DPPH) free radical scavenging activity was carried out to determine the antioxidant activity based on the scavenging ability of the stable DPPH free radical. Ethyl acetate extract of the seed exhibited the highest total phenolic content 0.8717 ± 0.003 mg GAE/g, followed by the methanol extract of the fruit (0.4065 ± 0.004 mg GAE/g), methanol extract of the seed (0.2947 ± 0.009 mg GAE/ g) and ethyl acetate extract of the fruit (0.1991 ± 0.089 mg GAE/g). These results were obtained using gallic acid as the standard (R2 = 0.9911). Crude ethyl acetate extract of seed showed the highest antioxidant activity among all four extracts (199.35 ± 0.056 mg/L), yet lower activity compared to that of standard L-Ascorbic acid (IC30 value; 35.45 mg/L). Additionally, the extracts showed a moderate correlation between the total phenolic content and antioxidant capacities of ethyl acetate and methanol extracts (p = 0.2582 and p = 0.6371) respectively. This study provides insight into the variation of phytochemical composition and antioxidant potential across different parts of the plant Tabernaemontana dichotoma. Further studies of these plant extracts could lead to an effective drug development from these plant extracts.