3.2. Assessment of antioxidant activity
The relationship between phenolic content and antioxidant capacity of the pitaya flesh and peel is shown in Fig. 2. Similar patterns were found in the antioxidant activity measured by ABTSradical dot+ assay. The effective concentrations (EC50) determined by DPPH radical-scavenging activity for flesh and peel were 22.4 ± 0.29 and 118 ± 4.12 μmol vitamin C equivalents/g dried extract, respectively, and the values of EC50 for the ABTS approach were 28.3 ± 0.83 and 175 ± 15.7 μmol TEAC/g dried extract, respectively. Peel extract was a better antioxidant than flesh due to its slightly higher polyphenolic content. The increase in phenolic content of the two extracts from flesh and peel was found to be linearly correlated with antioxidant capacity. In the DPPHradical dot assay, as the total phenolic compounds increased from 0.7 to 3.5 mg gallic acid equivalents of flesh and from 0.12 to 0.6 mg gallic acid equivalents of peel, the percentage of radical-scavenging activity of both increased linearly about 4.8-fold (R2 = 0.99).