New test measures foods’ antioxidant impact in the body; method is called a more accurate way to rank the anti-aging power of foods
by Craig Weatherby
For the past several years, “antioxidant” has ranked among the biggest buzzwords in food and supplement marketing.
Antioxidants are chemical compounds that neutralize “free radicals”: the unstable oxygen compounds that accelerate aging and promote cancer, heart disease, senility, and diabetes.
The body produces its own antioxidants—such as alpha lipoic acid and glutathione peroxidase—while other types of beneficial antioxidants occur abundantly in colorful plant foods.
Most fruits and vegetables contain the antioxidant vitamins E, C, and beta carotene (a precursor to vitamin A). But plant foods also contain compounds called flavonoids, many of which exert even stronger antioxidant effects.
(Unique among animal foods, Salmon is a major source of antioxidants. It's rich in the red-orange pigment called astaxanthin, which exerts antioxidant effects many times more powerful than those of vitamin E.)
Given the health concerns of aging baby boomers, it’s no surprise that marketers like to claim the antioxidant crown for novel products like pomegranate juice.
Thanks to differences in analytical methods and other factors, top antioxidant honors have rotated most recently among blueberries, pomegranate, cocoa, and the exotic Amazonian fruit called acai (ah-sigh-yee).
Rival antioxidant rankings: Comparing apples and oranges
The antioxidant activity of foods and plant compounds has been measured using one or more of three dominant methods: ferric reducing ability of plasma (FRAP), oxygen radical absorbance capacity (ORAC), and Trolox equivalent antioxidant capacity (TEAC).
There is considerable debate about which method is best, and it is critical to understand that these tests are done in test tubes, not in people.
Because there are different ways to measure antioxidant power, lists that rank foods on this score often differ from each other, leaving consumers seriously confused.
In addition, some lists compare foods by “typical serving size”—which can vary from ¼ teaspoon for spices to ½ cup for fruits and vegetables—while other lists compare uniform amounts of various foods, such as 100 grams.
Another part of the problem is the definition of “food”. Ounce for ounce, the antioxidant capacity of culinary herbs and spices such as mint, oregano, parsley, clove, and cardamom exceed that of any fruit or vegetable.
But most lists focus on fruits and vegetables because Americans consume them much more frequently and abundantly than culinary herbs and spices.
As we reported a while back, whole grains have been overlooked as substantial sources of antioxidants (see “Whole Grains: Under-Sung Antioxidant Aces”). Colorful beans are also rich in antioxidants, but, like whole grains, they tend to be left out of antioxidant-content charts.
New USDA rankings: Obsolete on arrival?
Earlier this month, scientists at the U.S. Department of Agriculture’s Agricultural Research Service (ARS) released measures of the “antioxidant capacity” of 277 selected foods.
The ARS team analyzed the fruits, nuts, vegetables and spices for their oxygen radical absorbance capacity (ORAC), which is one of a number of methods available to evaluate the antioxidant capacities of foods.
Antioxidant capacity measures may vary due to factors such the cultivar studied (e.g., wild versus cultivated blueberries) and its growing and harvesting conditions, as well as the methods used for a food sample’s preparation, processing, and/or analysis.
Recently, scientists at Cornell University proposed a new measure of antioxidant activity called the cellular antioxidant activity (CAA) assay, which they dubbed the “next step” in quantifying antioxidant activity.
The new CAA method tests antioxidant compounds’ activity inside cells: an approach that probably provides a more accurate gauge of the antioxidant power of whole foods and individual antioxidant nutrients and compounds.
New antioxidant test restores blueberries to top slot
Kelly Wolfe and Rui Hai Liu of Cornell University’s Food Science Lab developed the new method.
As Dr. Liu said in a press release, “We've taken the next step toward understanding antioxidant activity by examining how antioxidants react with cells. This new approach is more biologically relevant as it accounts for uptake, metabolism, distribution and activity of antioxidant compounds in cells versus solely looking at antioxidant value.”
They applied the new technique to equal amounts (100 grams) of wild blueberries, cranberries, apples, red and green grapes.
The results placed wild blueberries on top, followed by cranberries, apples, red grapes, and green grapes.
When they applied the CAA test to some of the most common flavonoids in plants foods, the researchers found that quercetin had the highest CAA value, followed by kaempferol (abundant in leeks), epigallocatechin gallate (EGCG, from green tea), myricetin, and luteolin, respectively.
Since quercetin showed the highest antioxidant capacity, it’s worth noting the top food sources of this flavonoid:
Top 20 Quercetin Sources (mg per 100 mg edible part*)
We hope that the Cornell team or others will follow this preliminary analysis with one that encompasses all of the top antioxidant contenders, including berries, herbs and spices, dark chocolate, and the full range of common fruits, vegetables, grains, and beans.
- Wolfe KL, Liu RH. Cellular antioxidant activity (CAA) assay for assessing antioxidants, foods, and dietary supplements. J Agric Food Chem. 2007 Oct 31;55(22):8896-907. Epub 2007 Sep 29.
- Bliss RM. Data on Food Antioxidants Aid Research. Accessed online December 16, 2007 at http://www.ars.usda.gov/is/pr/2007/071106.htm.
- USDA Database for Flavonoids for Selected Foods. Accessed online December 16, 2007 at http://www.nal.usda.gov/fnic/foodcomp/Data/Flav/flav.pdf