3.2.1. Reducing power
Reducing ability to convert Fe3+ to Fe2+ is an indirect evidence
for the antioxidant activity of an extract or a compound (Roy et al.,
2011). In the reducing power assay, the antioxidants, i.e. the reducing
species present in the solution causes the reduction of theFe3+/ferricyanide complex to form Fe2+ ions. This reaction was
monitored spectrophotometrically by recording the absorbance of
the reaction mixture at 700 nm (Barros et al., 2008). According to
the mentioned principle, the higher absorbance value at 700 nm is
gained, the stronger reducing power of the assayed sample shows.
Reducing power characteristics of ascorbic acid, astaxanthin and
astaxanthin/HPCD complex are shown in Fig. 5. Reducing powers
of the three samples were all enhanced along with the increase
of concentration among the tested range. The reducing power of
ascorbic acid was stronger than astaxanthin under the same concentration.
It has reported that astaxanthin was poorly soluble and
assembled in water (Köpsel et al., 2005). The assembled astaxanthin
molecules could not fully close and react with the Fe3+/ferricyanide
ions in the test. Nevertheless, the complexation made that astaxanthin
was completely dissolved in water. Hence, the reducing power
of the complex was stronger than that of native astaxanthin. Due to
the limits of solubility and sample quantity, the complex was only
tested at the concentration of 50 mol/L.