Banana peel extracts showed strong scavenging activity against
both DPPH (Table 2) and ABTS+ (Table 3) radicals. Extracts obtained with acetone:water had the highest antioxidant activity
compared with the other solvents assayed by a factor ranging between 1.3–1.9 (methanol) and 25–35 (acetone) for the DPPH assay
and a factor ranging between 2–4 (methanol) and around 10–35
(acetone and water in ‘‘Grande Naine”, and ethanol, acetone and
water in ‘‘Gruesa”) for the ABTS+ assay. The radical-scavenging
activity of the extracts obtained with acetone:water was superior
to 1.8 g TE or AE/100 g of freeze-dried residue powder. Although
ethanolic extracts showed higher DPPH inhibition percentages
than extracts obtained with acetone (4.5–5.5-fold greater), the
activities against ABTS+ radicals of the extracts obtained with
these solvents were very similar. The capacity to scavenge ABTS+
radicals was higher in ‘‘Gruesa” aqueous extracts than those obtained with ethanol and acetone. However, these aqueous extracts
showed no activity against DPPH radicals. This activity was similar
to that obtained by Llorach et al. (2002) for artichoke by-products
(0.15–0.95 g TE/100 g by-product), by Xu et al. (2008) for citrus
fruits peel (0.6–0.9 g TE/100 g DW by-product) or by Shui and
Leong (2006) for star fruit residue (3.4 g AE/100 g DW or 5.2 g
TE/100 g DW). Water pH (ranging between 3.0 and 8.0) did not affect scavenging activity. Prolonging extraction times (from 1 to
120 min), at 25 C, for extracts obtained using methanol, ethanol,
acetone, methanol:water, ethanol:water or acetone:water did not
lead to higher DPPH scavenging. At 55 C, the increase in extraction time doubled the antioxidant activity of the extracts obtained
with acetone.