Thermal treatments are generally regarded as being destructive
to antioxidants. Antioxidant activities of raw and cooked corn,
including FRAP and TEAC assays are presented in Table 1. Significant differences (p 6 0.05) in FRAP values were found among most
treatments. Boiled cut-kernels had the greatest decrease (57.4%),
followed by boiled whole-ears (46.3%), steamed cut-kernels
(29.4%), and steamed whole-ears (20.0%). The TEAC values were
similar to FRAP, however, the boiled whole-ear was not differed
with steamed cut-kernels. These results allow us to conclude
steam cooking preserved greater antioxidant content as compared
to the boiling in all treatments by all assays. Other studies have
suggested that boiling is generally regarded as being destructive
to antioxidant components (Krishnaswamy & Raghuramulu,
1998). On the contrary, the antioxidant activities were increased
for several vegetables such as carrots, spinach, mushroom, asparagus, broccoli and cabbage after thermal treatment (Halvorsen et al.,
2006). The loss in antioxidants from cooked corn can be attributed
to synergistic combinations or interactions of several types of
chemical reactions, diffusion of water soluble compounds, and
the formation or breakdown of them. Therefore, we investigated
the antioxidant activity of cooking water. Boiling water had high
antioxidant values, especially in water from boiled cut-kernels, followed by whole-ears; whereas, steaming water had low values of
both antioxidant activity assays (Tables 2 and 3). However, the
sum of antioxidant activity of the cooked corn and cooking water
is different from antioxidant activity of raw materials. These
results may suggest losses in their antioxidants are due to
breakdown of antioxidant compounds