The findings appear in the Feb. 26 print edition of the Journal of Agricultural and Food Chemistry, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society. The article was initially published Jan. 25 on the journal's Web site.
Flavonoids are phenolic compounds that have potent antioxidant activity. Many are produced in plants in response to environmental stressors, such as insects or competing plants.
"If an aphid is nibbling on a leaf, the plant produces phenolics to defend itself," says Alyson Mitchell, Ph.D., a food scientist at the University of California, Davis, and lead author of the paper. "Bitter or harsh phenolics guard the plant against these pests."
The need for these natural safeguards decreases with the use of herbicides and pesticides in conventional agriculture. This decrease is reflected in the total amount of antioxidants the plants produce. "This helps explain why the level of antioxidants is so much higher in organically grown food," Mitchell says. "By synthetically protecting the produce from these pests, we decrease their need to produce antioxidants. It suggests that maybe we are doing something to our food inadvertently."
Mitchell measured antioxidants found in corn, strawberries and a type of blackberry called a marionberry. "We started with these three due to plant availability," Mitchell explains, "but we intend to widen our search to include tomatoes, peppers, broccoli and a variety of other vegetables. We expect these results to be transferable to most produce."
The investigation compared the total antioxidants found in foods grown organically (using no herbicides, pesticides or fertilizers) to foods grown sustainably (in this study fertilizers but no herbicides or pesticides were used) and conventionally (using synthetic chemicals to protect the plants and increase yield).
The results showed a significant increase in antioxidants in organic and sustainably grown foods versus conventionally grown foods. The levels of antioxidants in sustainably grown corn were 58.5 percent higher than conventionally grown corn. Organically and sustainably grown marionberries had approximately 50 percent more antioxidants than conventionally grown berries. Sustainably and organically grown strawberries showed about 19 percent more antioxidants than conventionally grown strawberries.
Antioxidant levels were highest overall in sustainably grown produce, which indicates that a combination of organic and conventional practices yields the highest levels of antioxidants. "This may reflect the balance between adequate nutrition in the form of fertilizers and external pest pressures because of the lack of pesticides and herbicides," Mitchell explains.
"Originally, the question was just really intriguing to me," says Mitchell, whose research grew naturally from a personal interest in organic foods. "I found that the higher level of antioxidants is enough to have a significant impact on health and nutrition, and it's definitely changed the way I think about my food."
— Allison Byrum
Journal of Agricultural and Food Chemistry