A total of 927 freeze-dried vegetable samples, including 111 white cabbages, 59 carrots,
51 snap beans, 57 cauliflower, 33 white onions, 48 purple onions, 130 broccoli, 169
tomatoes, 25 beets, 88 peas, 88 spinach, 18 red peppers, and 50 green peppers, were
analyzed using the oxygen radical absorption capacity (ORAC) and ferric reducing antioxidant
capacity (FRAP) methods. The data show that the ORAC and FRAP values of vegetable
are not only dependent on species, but also highly dependent on geographical origin
and harvest time. The two antioxidant assay methods, ORAC and FRAP, also give different
antioxidant activity trends. The discrepancy is extensively discussed based on the
chemistry principles upon which these methods are built, and it is concluded that
the ORAC method is chemically more relevant to chain-breaking antioxidants activity,
while the FRAP has some drawbacks such as interference, reaction kinetics, and quantitation
methods. On the basis of the ORAC results, green pepper, spinach, purple onion, broccoli,
beet, and cauliflower are the leading sources of antioxidant activities against the
peroxyl radicals.