The ABTS assay is commonly applied to determine antioxidant
activity in plants. It is based on the ability of antioxidants to scavenge
the long-life radical cation ABTS+. The antioxidant activity of
the fibre concentrates extracted with methanol:acetone ranged
(p < 0.05) from 5.5 lM TE/g for passion fruit to 38.0 lM TE/g for
mango. The antioxidant activity of ethanol extracts were lower
(p < 0.05) than those of the methanol:acetone extracts, with values
ranging from 1.7 lMTE/g for pineapple to 15.3 lM TE/g for mango,
with no statistically significant differences (p > 0.05) between passion
fruit, pineapple and guava.
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.
There are no studies showing the antioxidant activities of the
co-products obtained from exotic fruit in general and the exotic
fruit studied here in particular. However there are numerous studies
where the antioxidant activities of fresh exotic fruit have been
determined. Thus, Beserra Almeida et al. (2011) reported that the
antioxidant activities of some exotic fruit from Brazil such as tamarind
(Tamarindus indica), papaya (Carica papaya) or murici (Byrsonima
crassifolia) were 8.3, 7.6 and 15.6 lM TE/g sample (fresh
weight), respectively, as measured with the ABTS assay, while
the DPPH assay gave values of 2.0; 2.2 and 6.5 lM TE/g sample
(fresh weight), respectively. Vasco et al. (2008) showed that the