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Ron Prior, PhD, a researcher at the USDA???s Arkansas Children???s Nutrition Center (Little Rock, AR) who has conducted a significant body of research correlating the relationship between the composition of agricultural produce and the effects on health, noted in his findings that ???among all common fruits and vegetables in the diet, berries, especially those with dark blue and red colors, have the highest antioxidant capacities.???1 This mention of color is important because anthocyanins, a class of flavonoids, are also responsible for the red to dark blue pigmentation in many plants. These anthocyanins, along with proanthocyanidins, are among the major phytochemicals common across berries and are known to be effective antioxidants.
A current practice is to measure antioxidant capacity using methods such as oxygen radical absorbance capacity (ORAC), troloxequivaent antioxidant capacity (TEAC), and ferric-reducing ability of plasma (FRAP). These tools improved upon the quantification of the compounds in natural products by giving us the added dimension of measuring antioxidant activity, but they are insufficient for what we really need, which is identification of the actual effects on body function or a disease state. For this we need to progress to better physiological assays and clinical trials.
Arguably the ORAC method is the most commonly used for measuring antioxidant capacity; for this reason it is important to be aware of the pitfalls and misuses of the method. For instance, there are significant variations in the assay itself. We have seen as much as 25% variation in values coming from the same independent lab on the same lot, completed in the same lab run. The researchers themselves have cautioned against overreliance on published studies for comparative purposes, noting that changes in methods, limited sample sizes, variations in growing conditions of the produce, and wide variations in antioxidant activity between cultivars (varieties of the species) make it difficult to form a valid comparison. An example of the latter is blueberries, which have high ORAC values on the average, but some cultivars have very little antioxidant activity. Who knows what cultivar is on their plate?
More troubling is how values of antioxidant activity are used in advertising. Too often, ads proclaiming a particular fruit to have ???the highest antioxidant activity??? are sponsored by a manufacturer or grower???s association that may change the unit of measure or serving size, ignore the difference between fresh and dry weight, and/or ignore more recent analyses therefore casting their fruit or product in the most flattering light.
They are, after all, chemical assays that give us a benchmark of an ingredient???s radical scavenging potential, appropriately used for this purpose. But they do not tell us what happens physiol









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