Not all black raspberries are alike when it comes to cancer-fighting qualities.

Those are the findings of Ohio State University researcher Joe Scheerens, who with his colleagues analyzed four common cultivars grown at eight different production areas in the state.

The findings suggest that phytonutrient properties may be influenced by how the crop is grown and harvested and by the environmental and soil conditions present at the growing site, according to a news release.

The study, "Antioxidant Capacity and Phenolic Antioxidants of Midwestern Black Raspberries Grown for Direct Markets Are Influenced by Production Site," was published in a recent issue of the journal HortScience.

Joe Scheerens, horticulture and crop science researcher in Wooster, says the findings might help growers produce berries with optimum cancer-fighting compounds, both for use in medical studies as well as for purchase by the general consumer.

"If you are going to create clinical products used to treat degenerative diseases, one of the things that becomes paramount is to have a consistent supply of berries with a reproducible amount of bioactive ingredients," says Scheerens, who is part of the university's crop-to-clinic research project.

The research is examing how berries might be used to prevent or slow the development of certain cancers of the mouth, throat and digestive tract.

"In addition, if we understand how the plant reacts to cultural or environmental stresses, we can couple this information with current medical research to guide farmers on how to produce berries that provide the optimum health benefits," he says.

Schereens and his colleagues speculate that environmental stresses, such as heat, light and water availability, play a role in antioxidant production.

"Anytime the plants feel stressed, they make antioxidants," he says. "But how a plant like the black raspberry reacts to environmental conditions is complex and involves the regulation of genes that control the production of plant products like antioxidants. It's this process we are still trying to learn more about."

But too much stress also can be bad.

Researchers found that at production sites where the soil temperature was consistently high, antioxidant levels were the lowest.

"It could be that the stress from consistently high soil temperatures is too much for the plant to overcome, and antioxidant accumulation is actually inhibited," Scheerens says.

Researchers also found that the state of fruit ripeness has an effect on antioxidant content, suggesting that harvest timing is important.

"When we explored this relationship with additional research, we found that anthocyanins, the pigments that are the primary antioxidants in black raspberries, increased as much as 15 percent as the berries progressed through the last two stages of ripening," Scheerens says.

Scheerens said that these two stages were separated by 48 hours or less and could be distinguished only by the "finger force" required to remove the berry.

The cultivars Bristol, Jewel, MacBlack and Haut were used in the study.