Some organically grown fruits and vegetables contain as much as 58 percent more antioxidants than conventionally grown produce, research from the University of California, Davis indicates.

The study was published in the Feb. 26 Journal of Agricultural and Food Chemistry, a peer-reviewed journal of the American Chemical Society.

Researchers found that organically or sustainably grown corn, strawberries and marionberries (a type of blackberry) contain more polyphenolics, which are natural antioxidants produced by plants as a defense against insects and other pests. The study suggests that herbicides and pesticides decrease the need for these natural antioxidants.

The level of antioxidants in sustainably grown corn was 58.5 percent higher than in conventionally grown corn, while organically and sustainably grown marionberries had 50 percent more antioxidants. Organically and sustainably grown strawberries had 19 percent more antioxidants than their conventional cousins did.

Researchers also found that frozen strawberries, marionberries and corn have higher levels of polyphenolics than freeze-dried or air-dried versions.

The organic foods in the study were grown without herbicides, pesticides or synthetic fertilizers, while the sustainable produce was grown with fertilizer but without herbicides or pesticides.

Researchers concluded that antioxidant levels were highest in sustainably grown produce. "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," said Alyson Mitchell, assistant professor of food science at UC Davis and leader of the research team.

Mitchell said researchers plan to widen their study to other vegetables, but believe the results will be the same in most produce.

Bob Scowcroft, executive director of the Organic Farming Research Foundation, said the study is a good beginning and establishes research protocols for further studies.

"It's opened the field to numerous questions—is it the stress to the plants that did this? Will any fertilizer work? Now additional researchers need to see if they can replicate these findings," he said.