The DPPH free-radical does not require any special preparation
and is considered a simple and very fast method for determining
antioxidant activity. In contrast, DPPH can only be dissolved in organic
media, especially in ethanol, which is an important limitation
when interpreting the role of hydrophilic antioxidants. In the DPPH
assay the antioxidant capacities of the exotic fruit extracts tested
varied from 4.8 to 47.1 lM TE/g for pineapple and mango, respectively,
with statistically significant differences (p < 0.05) between
samples. As occurred with the ABTS assay (ethanol extraction),
the antioxidant activity values were lower (p < 0.05) than those
found in the methanol:acetone extract, with values ranging from
1.5 lM TE/g for passion fruit to 31.7 lM TE/g for mango with no
statistically significant differences (p > 0.05) between passion fruit
and pineapple samples.
The FRAP assay is commonly used to study the antioxidant
capacity of plant materials. The antioxidant capacity of fruit
extracts is determined by the ability of the antioxidants in these
extracts to reduce ferric to ferrous iron in FRAP reagent. The analysed
exotic fruit co-products showed a wide range of antioxidant
capacities, with values for ethanol extracts ranging between
2.5 lM TE/g for passion fruit and 13.7 lM TE/g for mango with statistically
significant differences (p < 0.05) between samples. In the
methanol:acetone extracts, the antioxidant activity values ranged
between 6.2 lM TE/g for pineapple and 19.1 lM TE/g for mango,
with statistically significant differences (p < 0.05) between samples.
As in the case of ABTS and DPPH in ethanol extracts, the antioxidant
activity values were lower (p < 0.05) than those when the
extraction used methanol:acetone.