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30 min. Absorbance at

765 nm was measured against a reagent blank. If the sample absorbance exceeded 1, the sample was appropriately diluted to give reading less than 1. A standard calibration curve was prepared using gallic acid. Total phenolic contents were expressed in gallic acid equivalents, GAE, in mg per

100 g fresh fruit. Since ascorbic acid was responsible to the formation of the blue molybdenum C tungsten complex, the absorbance originating from it was corrected by preparing ascorbic calibration curve. An ascorbic calibration curve was therefore prepared. The total phenolic content reported was corrected for ascorbic acid. Free radical scavenging activity assay Free radical scavenging activity was determined according to the method of Suja et al. [18] with slight modification. Fruit extract (1 mL) was added to

2 mL DPPH solution (2mL of 0.02g/L DPPH) in ethanol. The reduction of DPPH was measured at

517 nm against a blank assay at

30 min. The percentage of remaining radical in medium is calculated as the absorbance of the sample divided by that of DPPH control at the same time multiplied by 100. The amount of sample needed to decrease the initial DPPH concentration by 50%, EC50, was calculated graphically. The anti-radical power (ARP) of extract was calculated as ARP =

1 / EC50 Ferrous ion chelating activity Ferrous ion chelating activity was determined according to the method of Lim et al. [19]. Iron sulphate (2 mM) and ferrozine (5 mM) were prepared and diluted

20 times. Fruit extract (1mL) were mixed with diluted FeSO4 (1 mL), followed by diluted ferrozine (1 mL). The tubes were mixed well and allowed to stand for

10 min at room temperature. Absorbance of each extract was measured against blank at

562 nm. The ability of the sample to chelate ferrous ions was calculated and expressed as: Chelating effect (%) = (Acontrol C Asample) / Acontrol x

100 Wee Sim Choo et al Adv. Appl. Sci. Res., 2011,

2 (3): 418-425

421 Pelagia Research Library Statistical analysis Results were expressed as the means ± standard deviation of three replicates. Data were interpreted by one-way analysis of variance (ANOVA) with Duncan'

s multiple-range test using SAS software package (SAS Institute Inc., Cary, NC, USA). The statistical significant was evaluated at p <

0.05 level. RESULTS AND DISCUSSION Ascorbic acid content The two species of Hylocereus fruits showed higher ascorbic acid contents in pulps than in fruits (peels and pulps) [Table 1]. This indicates that more ascorbic acids were found in the pulps than in the peels of the two species of Hylocereus. There were no significant differences (p <

0.05) in the ascorbic acid contents of the pulps of H. polyrhizus and H. undatus. However, the ascorbic acid contents of fruits (peels and pulps) of H. polyrhizus were higher than those of H. undatus. These results are not in accordance with the study of Mahattanatawee et al. [8] where the ascorbic acid content of pulp of H. undatus (55.8 ± 2.0 mg/100g puree) was found to be higher than that of H. polyrhizus (13.0 ± 1.5 mg/100g puree). This difference was most likely due to different sample preparation method and different experimental method to determine ascorbic acid content. Mahattanatawee et al. [8] extracted the fr........