Analysis of Food-based Antioxidants
The mango is partly coloured by beta carotene (445 micrograms/100 g). It also contains 1.7 mg catechin /100 g Although cauliflower does not contain a significant quantity of glucoraphanin (precursor of sulforaphane), in common with broccoli it contains glucobrassicin and neoglucobrassicin glucosinolates.
Potency of the chemical classes of antioxidants
Antioxidant potency is measured as Trolox Equivalent Antioxidant Capacity (TEAC) Analytical biochemistry
There are 4 chemical classes of antioxidant, in order of their potency (solubility in brackets), they are:-

Polyphenols (hydrophilic) > Carotenoids (lipophilic) > Vitamin E (lipophilic) > Vitamin C (hydrophilic)

The potency of vitamin C is taken as 1 (see below).
Potency of individual antioxidants
AntioxidantQuantityPotencyTAC units
(source - apples)(mg/100g)(VCEAC values)(per 100g apple)
Quercetin glycosides13.203.0640.39
Epicatechin8.652.6723.10
Procyanidin B(2)9.352.3622.07
Phloretin glycosides5.591.6312.80
Vitamin C12.80(1.00)9.11
Chlorogenic acid9.020.978.75
Source reference
Reprinted with permission, from K.W. Lee, et al., J. Agric. Food Chem., 2003, 51(22), 6516-20. Copyright 2003, ACS Publications.

Comment

From these data, the members of the group of quercetin glycosides have approximately 3 times the potency of vitamin C (see also Phytochemistry), whereas chlorogenic acid is approximately equal to vitamin C. The questions yet to be answered are, "are the quercetin glycosides 3 times as effective as vitamin C in their therapeutic properties?" And, "could chlorogenic acid be much less therapeutic than vitamin C?" This is the sort of information that is needed in order to progress towards the determination of the effectiveness of individual antioxidants as free radical scavengers.

Recent developments

1. Resveratrol was found to be more potent than curcumin, which was found to be more potent than genistein.
V. Jefremov et al., Ann. N.Y. Acad. Sci. 1095, (2007) 449-457.

2. A recent paper gives a list of antioxidant capacities derived by the CUPRAC method (see also Analytical developments), in descending order of potency, viz. epicatechin gallate > epigallocatechin gallate > quercetin > fisetin > epigallocatechin > catechin > caffeic acid > epicatechin > gallic acid > rutin > chlorogenic acid.
R. Apak et al., Microchim. Acta, eFIRST, 21 May 2007.

3. 15 bilberry anthocyanins and 3 glucopyranosides were studied to explore structure/antioxidant potency in relation to the superoxide radical :- delphinidin > petunidin > malvidin:cyanidin > (+)-catechin > peonidin > pelargonidin. In relation to the peroxynitrite radical:delphinidin > cyanidin:petunidin > malvidin (+)-catechin > peonidin > pelargonidin. Further evidence of the high activity of the 3',4'-dihydroxy group was obtained when the 4'-O-Me substituted delphinidin markedly lost activity.
M.M. Rahman et al., Free Radic. Res. 40(9) 993-1002, 2006. [Permission granted from Taylor and Francis web site]
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