"This really opens the door to more research in this area," said Alyson Mitchell, assistant professor of food science at UC Davis, who led the research team. The researchers compared levels of total polyphenolics and ascorbic acid content in marionberries (a type of blackberry) and corn grown organically, sustainably or conventionally, and in strawberries grown sustainably or conventionally. The fruits and corn used were frozen, freeze-dried or air-dried.
Frozen sustainably-grown and organic marionberries and corn contained 50 to 58 percent more polyphenolics than conventionally grown crops from neighboring plots. Sustainably-grown frozen strawberries contained 19 percent more polyphenolics than conventional fruit. Sustainably-grown and organic produce also had higher levels of ascorbic acid.
Frozen fruit and corn tended to have higher levels of polyphenolics than freeze-dried or air-dried foods.
The polyphenolics in the organic crops were at levels you would expect to see in wild plants, suggesting that pesticide use reduces the need for plants to make these chemicals, Mitchell said
Polyphenolics are natural chemicals produced by plants as by products of other processes. When plants are stressed, for example by insects, they produce higher levels of polyphenolics, which can taste bitter, to drive away pests.
Studies show that eating a diet rich in fruit and vegetables, which is high in polyphenolics can reduce the risk of some cancers and heart disease. But scientists don't know exactly how polyphenolics cause these effects.
"We know they're beneficial, but we don't know what types of polyphenolics are beneficial , or in what quantities," Mitchell said.
The organic foods were grown according to the definition set by the U.S. Department of Agriculture, without artificial pesticides or fertilizers used in conventional farming. Sustainably-grown produce was grown with artificial fertilizers, but without pesticides.
Total polyphenolics levels were slightly higher in sustainably grown produce, suggesting that a combination of organic and conventional practices yields the highest levels. Crops grown without using pesticides or herbicides might make more polyphenolics because they are more likely to be stressed by insects or other pests, Mitchell said.
"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," she said.
The research, which was partly supported by a gift from Oregon Freeze-Dry Inc., was published in the Feb. 26 edition of the Journal of Agricultural and Food Chemistry.
Journal
Journal of Agricultural and Food Chemistry