Bioactive Compounds and Total Antioxidant Capacity of Different Tissues of Two Pitaya (Dragon Fruit) Species Grown in Sri Lanka

Bioactive compounds (viz. total phenolics, total flavonoids and vitamin C) and total antioxidant capacity (TAC) of flesh and peel of two dragon fruit species namely, Hylocereus polyrhizus (red-fleshed) and Hylocereus undatus (white-fleshed) were investigated. TAC was determined by Ferric reducing antioxidant power (FRAP) assay. Colorimetric methods were used to determine total phenolic (Folin-ciocalteu method) and total flavonoid contents whereas vitamin C content was measured using a titration method (titration with 2,6-dichloro-phenolindophenol dye). Several selected physical and chemical properties of the two dragon fruit species were also determined. Flesh of red-fleshed dragon fruit had significantly higher amounts of total phenolics (51.80 + 1.64 mg GAE/100 g FW) and total flavonoids (46.29 + 2.47 mg RE/100 g FW) and higher TAC (67.25 + 3.20 mg TE /100 g FW), whereas higher vitamin C content (31.11 + 3.85 mg / 100 g FW) was observed in flesh of white-fleshed dragon fruit. Flesh of two dragon fruit species showed significantly higher bioactive compounds and TAC than their peels. Significantly higher linear relationships were found between the TAC values and the total phenolic content (R2 = 0.907, p<0.001) and total flavonoid content (R2 = 0.888, p<0.001). However TAC poorly correlated with vitamin C content. Findings of the current study indicate that flesh of both dragon fruit species contained higher amounts of total phenolic, total flavonoid, vitamin C contents and higher TAC than peel. Significantly, higher total phenolic, total flavonoid contents and TAC were observed in flesh of red-fleshed dragon fruit than in white-fleshed dragon fruits. Flesh of white-fleshed dragon fruit had high vitamin C content, compared to red-fleshed dragon fruits.