technique with some modifications. The stock solution was prepared
by mixing 2.5 mg of DPPH radical with 100 mL of methanol.
The solution absorbance was adjusted at 0.7 ± 0.02 in 515 nm using
an UV–Vis spectrophotometer PerkinElmer Lambda 11. 3.9 mL of
DPPH radical were placed in a test tube and 100 lL of the antioxidants
extract or standard were added (methanol was used as
blank). The decrease in absorbance at 515 nm was measured at
1 min intervals for the first 10 min, and then at 5 min intervals
until stabilization. Based on a preliminary study, the time required
to obtain DPPH readings of each fruit peel was 30 min. Two calibration
curves were prepared using Trolox and ascorbic acid as standards
and results (AOC) are expressed as lM Trolox equivalents/
100 g of DW and ascorbic acid equivalents in mg/100 g of DW.
The ABTS (2,20
-Azinobis-3-ethylbenzotiazoline-6-sulphonic
acid) assay was conducted according to Miller, Rice-Evans, Davies,
Gopinathan, and Milner (1993). ABTS+ cation was generated
through the interaction of 19.2 mg of ABTS dissolved in 5 mL of
HPLC-grade water and 88 lL of 0.0378 g/mL potassium persulfate
(K2S2O8). The cation was incubated in the dark at room temperature
for 16 h. The ABTS activated radical was diluted with ethanol to an
absorbance of 0.70 ± 0.02 at 734 nm. After the addition of 30 lL of
antioxidants extract or standard to 2970 lL of diluted ABTS solution,
absorbances were recorded 6 min after mixing. Two calibration
curves were prepared using Trolox and ascorbic acid as a
standard and results (AOC) are expressed as lM Trolox equivalents/100
g of DW and ascorbic acid equivalents in mg/100 g of DW.