Ferric reducing activity based on FRAP assay
The FRAP assay measures the reducing
potential of an antioxidant reacting with a ferric
tripyridyltriazine (Fe3+–TPTZ) complex and
producing a coloured ferrous tripyridyltriazine (Fe2+–
TPTZ) (Benzie and Strain, 1996). FRAP values of
the kaffir lime leaves are shown in Table 2. The
mean FRAP values of the studied cooking method
showed that steaming > boiling > fresh ≈ deep frying
≈ roasting > blanching ≈ hot-air drying. Similar
results to DPPH, TPC and TFC, steaming gave the
highest values of FRAP (628 μmol FeSO4/g) (Table
3). Our findings support the results from previous
study of Wachtel-Galor et al., (2008) that steaming
cooking increases the antioxidant activity of selected
vegetables in their study. For thermal process, heat is
transferred more slowly by hot air than by hot water
because of differences in heat conductivity. In some
cases, decomposition of antioxidants during heating