Ferric ion reducing activity
The ability of the plants extracts to reduce ferric ions
was determined using the FRAP assay developed by Benzie
and Strain (1996). An antioxidant capable of donating a
single electron to the ferric-TPTZ (Fe(III)-TPTZ) complex
would cause the reduction of this complex into the blue ferrous-
TPTZ (Fe(II)-TPTZ) complex which absorbs strongly
at 593 nm.
The trend for ferric ions reducing activities of the 25
plants did not vary markedly from their DPPH free radical
scavenging activities, when a comparison betweeen Figs. 1
and 2 was made. Similar to the results obtained for the
DPPH free radical scavenging assay; mint, laksa, tapioca,
daun salam, sweet potato, cekur manis and betel leaves
showed relatively strong ferric ion reducing activities.
Interestingly, TEACFRAP values were consistently higher
than those obtained for TEACDPPH. Gil, Toma´s-Barbera´n,
Hess-Pierce, and Kader (2002) reported a similar trend
where the DPPH free radical scavenging activities of stone
fruits, expressed as ascorbic acid equivalents, were higher
than their corresponding ferric ion reducing activities.
The probable reason for the lower TEACDPPH values of
the plants could be due to the presence of compounds not
reactive towards DPPH. Antioxidant compounds such as
polyphenols may be more efficient reducing agents for ferric
iron but some may not scavenge DPPH free radicals as
efficiently due to steric hindrance. In this study, local celery