Optimization of extraction conditions by the dosage of polyphenols and determination of antioxidant activity: Case of Melothria maderaspatana organs, a plant used in traditional African medicine for the treatment of diabetes

Abstract

Melothria maderaspatana is a medicinal plant of Asian origin belonging to the Cucurbitaceae family. It has a wide range of phytochemicals such as alkaloids, flavonoids, tannins, saponins, steroids, terpenoids, phenolic compounds. The leaves, roots and fruits are considered to have stomachic activities. It is a plant very rich in phenolic compounds, generally responsible for the biological activity of plants. In this study, we optimized the extraction parameters, including temperature, duration and solvent mass/volume ratio, by determining the total polyphenol contents and the antiradical activity at DPPH●. The Folin-Ciocalteu reagent was used to evaluate the content of phenolic compounds, with gallic acid as a reference. The determination of flavonoids with AlCl3 was carried out with quercetin as a reference. The DPPH● radical made it possible to measure the antioxidant power of the extract, with reference to Trolox. This study showed that the optimal conditions for extraction of bioactive molecules, responsible for antioxidant activity, are obtained for a temperature of 80 °C, for a period of 30 min in a ratio of 1 g for 50 mL of extraction solvent which is distilled water. Under these conditions, the contents of total polyphenols and flavonoids are evaluated for the other organs of the plant. The values obtained ​​show that the three parts of the plant contain approximately the same polyphenol contents and exhibit the same DPPH● antioxidant activity. As for the flavonoid content, the leaves are revealed to be the richest part, compared to the stems and fruits. These physicochemical indicators in secondary metabolites and biological activity justify the primary choice reserved for this plant by traditional practitioners for the treatment of numerous pathologies.