In this meta-analysis of 343 peer-reviewed publications, organic crops contained 17-69% percent more antioxidants than conventionally grown crops. For some classes of antioxidants, the difference was larger. A group of compounds known as flavanones, for example, were 69 percent higher in the organic produce. (At very high quantities, as in some supplements, some antioxidants have been shown to be harmful, but the levels in organic produce were not nearly that high.)
Concentrations of a range of antioxidants such as polyphenolics were found to be substantially higher in organic crops/crop-based foods, with those of phenolic acids, flavanones, stilbenes, flavones, flavonols and anthocyanins being an estimated 19%, 69%, 28%, 26%, 50% and 51% higher, respectively.
The frequency of occurrence of pesticide residues was found to be 4 times higher in conventional crops.
The findings fit with the expectation that without pesticides, plants would produce more antioxidants, many of which serve as defenses against pests and disease.
Study of Organic Crops Finds Fewer Pesticides and More Antioxidants. NYTimes http://buff.ly/1tCdl2Q
Higher antioxidant and lower cadmium concentrations and lower incidence of pesticide residues in organically grown crops: a systematic literature review and meta-analyses. Br J Nutr. 2014 Jun 26:1-18. [Epub ahead of print]