Study on the content of some metals in soil by XRF method and evaluating their effect on the total phenolic and flavonoid content of methanol extracts from two medicinal plants in An Giang Province

Several metals in soil affect the production of secondary metabolites in medicinal plants. In this study, we have determined concentrations of K, Mn, Fe, Zn, Cu in soils collected at Tinh Bien, Tri Ton, Thoai Son, and Cam Mountain areas in An Giang province by X-Ray Fluorescence Spectroscopy (XRF). We simultaneously evaluated the total phenolic and flavonoid content of methanol extracts from Solanum torvum (Sw.) leaves and Zingiber zerumbet (L.) rhizomes harvested in Tinh Bien and Cam Mountain. The results showed that the concentrations of metals reached the highest values at the soil particle size 0.25 mm among three sizes: 0.25 mm, 1 mm, and 2 mm. Whereas, the metal contents at two sampling depths 0-15 cm and 15-30 cm were similar. The concentrations of K and Cu in the soil in Tinh Bien are higher than Cam Mountain at 1.18 times and 1.70 times; however, the Fe, Zn, Mn content in Tinh Bien is lower at 2.16 times, 1.64 times, and 1.43 times. Thereby, it can be seen that the higher concentration of K and Cu may contribute to increasing the total phenolic content about 1.8 times with the Zingiber zerumbet (L.) rhizomes sample, and the flavonoid content by 2.5 times for the Solanum torvum (Sw.) leaves sample in Tinh Bien compared to Cam Mountain. Meanwhile, the concentrations of Fe, Zn, and Mn did not affect the flavonoid and phenolic content in these two plants