Total phenolic, flavonoid, flavonol contents and antioxidant activity of inca peanut (Plukenetia volubilis l.) leaves extracts

Abstract

Inca peanut (Plukenetia volubilis L.) leaves were used to make tea and sold as a local product in Thailand but there is no research on the bioactivity of Inca peanut leaves. The present study was carried out to evaluate the phytochemical constituents and antioxidant activity of Inca peanut leaves. Fresh leaves were extracted with water (FW) and hot water (FH). Dried leaves (DH), roasted leaves (RH) and commercial tea leaves (CH) were extracted with hot water. Their phytochemical constituents, the amount of phenolic compounds (TPC), total flavonoid content (TFC) and total flavonol content (TFoC) were analyzed. The in vitro antioxidant activity was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and 2,2-azinobis (3-ethylbenzothiazoline 6-sulfonic acid) (ABTS) radical cation scavenging activity. The phytochemical screening revealed the presence of phenols, flavonoids, tannin, cardiac glycosides, steroids, and terpenoids. RH contained the highest TPC (21.36±1.90 µg GAE/mg), TFC (8.65±0.16 µg QE/mg), TFoC (0.249±0.004 µg QE/mg) and exhibited the most potent antioxidant activity by DPPH assay (IC50 = 135.97±6.71 µg/mL) and ABTS assay (IC50 = 37.53±3.87 µg/mL). Flavonoid has a positive correlation with DPPH radical scavenging activity. These results suggested that the antioxidant activity of Inca peanut leaves might be attributed to the presence of flavonoid compounds. Roasted leaves extract exhibited the highest antioxidant activities. Therefore, Inca peanut leaves extracts could be considered as a good source of antioxidant and developed as a functional food.