The list of total antioxidant capacity (TAC) values of some common foods on the Total antioxidants page may require further explanation.

1. Compare helpings
The herbs and spices are academically the highest sources of total antioxidants. However, the amount that would be required per serving is extremely small but nevertheless giving a useful antioxidant boost to the meal. Similarly, although cocoa powder contains 82,600 units per 100 g, you would use around 10 g of cocoa powder to make a drink, getting 8,250 TAC units, about the same as eating 100 g prunes. [Note: Some researchers report their results as per helping, but helping sizes vary. At this site the quantities are reported per 100 g food.] You may choose to drink a mug of cocoa rather than eating a serving of prunes to get the same amount of antioxidant. However, organic acids, such as oxalic acid, present in cocoa powder and contributing to the TAC value also possess the antinutritional property of occluding minerals and vitamins, preventing their absorption and utilisation. [see note 5 below]

2. Analytical differences expected for each commodity
All the values are for fresh food (except where stated), but different varieties, growing conditions (Country of origin, soil type, temperature, organic husbandry, etc.) storage and transportation histories will change the number of TAC units in the food you buy. So these values are only approximate for each commodity.

3. Ranking of known, comparable values
Among the foods listed here, are the super foods with upwards of 10,000 TAC units per 100 g food; acai (> 100,000 TAC units), herbs and spices (up to 300,000 TAC units, but see note 1 above regarding helping sizes), cocoa products, rice bran, pecan nuts, chokeberries and kidney beans. Among the super foods listed elsewhere are:- gogi berries. Fruits and other nuts occupy the middle positions in the list, and vegetables generally come lower down the table. However, the high acidity of fruits may have adverse effects on the quality of the total antioxidant load. For example, eating 100 g prunes may not be as convenient as eating 50 g kidney beans to get approximately the same number of TAC units, although both foods have their drawbacks!. Finally, not all foods have been tested for total antioxidant capacity yet, so the absence of a food from the lists does not mean that it necessarily has a lower value than those included.

4. Methodological differences
These data are taken from a recent source using total antioxidant capacity values rather than earlier ORAC (oxygen radical absorbance capacity) values which did not include the lipophilic fraction of antioxidants. There are several other methods extant, e.g. Vitamin C Equivalent Antioxidant Capacity (VCEAC), and they all give different values to the antioxidant content of a chosen food. see Analytical enigma. For a review of the current methodology see J. Agric. Food Chem., 53, (6), 1841-1856, 2005. At this early stage in the popularisation of antioxidant values as a measure of the potency of a foodstuff, the scientific data are difficult to correlate.

5. Antioxidant quality - are there good and bad antioxidants?
The total antioxidant capacity does not tell the whole story, and is only a rough guide until individual antioxidant values become readily available. This is exemplified by the presence of tomatoes at the bottom of the TAC list. [see Total antioxidants in foods]. However, tomatoes are a rich source of lycopene and beta carotene which are carotenoid antioxidants, and may be more important than the proanthocyanidins of cocoa powder in the treatment of certain cancers (However, go to >>>> Bad list. Furthermore, it may transpire that apart from the therapeutic proanthocyanidins in cocoa powder there may be high concentrations of antinutritional substances, like oxalic acid, contributing to the antioxidant capacity value.
A good example is the comparison between prunes (rich in carotenoids) and blueberries (rich in anthocyanidins). Recent work has shown that although prunes have a similar total antioxidant content to blueberries, their antioxidants are not bioavailable, whereas those of blueberries are.

6. Bioavailability
To be effective, once the antioxidant enters the digestive tract, it has to be absorbed into the blood stream where it has to exhibit antioxidant capacity. Furthermore, the increase in antioxidant capacity has to lead to a reduction in oxidative stress caused by an excess of free radicals. go to >>>> Antioxidant bioavailability