Cupper ion chelation activity
The TMM indicator has been used to determine the
ability of components in food samples and plant extracts
to sequester the free metal ions. In this study, cupric ions
were chosen over ferrous ions because the latter were less
redox stable at ambient conditions. Transition metal ions
such as those of copper and iron are important catalysts
for the generation of highly reactive hydroxyl radicals via
the Fenton reaction in both in vivo and in vitro systems.
Ligands that bind to metal ions can alter the redox potentials
of these ions, which would render the ions catalytically
silent. As secondary antioxidants, compounds can act as
effective ligands that sequester copper and ferrous ions by
‘‘wrapping’’ themselves around these ions. These ligands
could help intercept and suppress radicals formed via catalysis
from fuelling a chain reaction (Aruoma, Grootveld, &
Halliwell, 1987). Free hydroxyl groups in the flavonoid
ligands chelating the central metal ion may scavenge free
radicals.
The ability to chelate cupric ions varied widely for the
plants tested – daun salam chelated the least amount of
cupric ions while petai chelated the most. The cupric ions
chelating abilities of the plants used in this study, given
in Fig. 4, had not been reported before. The ability to