Fig. 5

Tannins, phenolics, flavonoid content, and antioxidant capacity by FRAP of Vinca rosea plants raised under different crude oil treatment levels of 0% (control), 1%, 3%, 5%, and 7% at the end of a 5-month experimental time. A Tannin content of shoot and root, B phenolic content in shoots, C flavonoid content in shoots, and D antioxidant capacity. The shown curves A and B are the polynomial regression (order 3) of flavonoid and phenolic content against the percentage of crude oil treatment. Different letters indicate significant differences between different treatments at p ≤ 0.05. Values are expressed as mean ± SE (n = 3)