The Colour Purple

Compounds that colour fruits may protect against cancer

Understanding the molecular structures of compounds that give certain fruits and vegetables their rich colours may help researchers find even more powerful cancer fighters.

Anthocyanins, the compounds that give colour to purple, red and blue fruits and vegetables—some of which are also commonly used as dyes—can significantly slow the growth of cancer cells.

“These foods contain many compounds, and we're just starting to figure out what they are and which ones provide the best health benefits,” said Monica Giusti, the lead author of the study and an assistant professor of food science at Ohio State University.

Giusti and her colleagues found that in some cases, slight alterations to the structure of anthocyanin molecules made these compounds more potent anti-cancer agents. The finding brings scientists a step closer to figuring out exactly what properties in fruits and vegetables give them their cancer-fighting capacity.

The anti-cancer effects of anthocyanin-rich extracts from a variety of produce were tested. They retrieved these anthocyanins from some relatively exotic fruits and other plants, including grapes, radishes, purple corn, bilberries, purple carrots and elderberries.

The plants were chosen due to their extremely deep colours, and therefore high anthocyanin content. The researchers added different extracts to flasks that contained colon cancer cells. They used an analytical technique called high-performance liquid chromatography – mass spectrometry in order to determine the exact chemical structure of each compound. They used biological tests to determine the number of cancer cells left after anthocyanin treatment.

Researchers found that the amount of anthocyanin extract needed to reduce cancer cell growth by 50 percent varied among the plants. Extract derived from purple corn was the most potent, in that it took the least amount of extract to cut cell numbers in half.

In additional laboratory studies, she and her colleagues found that anthocyanin pigments from radish and black carrots slowed the growth of cancer cells anywhere from 50 to 80 percent. But pigments from purple corn and chokeberries not only completely stopped the growth of cancer cells, but also killed roughly 20 percent of the cancer cells while having little effect on healthy cells.

“All fruits and vegetables that are rich in anthocyanins have compounds that can slow down the growth of colon cancer cells, whether in experiments in laboratory dishes or inside the body,” Giusti said. There may be relatively simple ways to implement these new findings.

“There are more than 600 different anthocyanins found in nature,” Giusti said. “While we know that the concentration of anthocyanins in the GI tract is ultimately affected by their chemical structures, we're just beginning to scratch the surface of understanding how the body absorbs and uses these different structures.”

“It is possible to use natural, anthocyanin-based food colourants instead of synthetic dyes,” Giusti said. “Doing so still maintains the wonderful colours of foods while enhancing their health-promoting properties.”

Previous research at Ohio State found that black raspberries appear to reduce the growth of esophageal and colon cancers tumors.

The team is also evaluating how these pigments interact with other compounds in foods – such interactions could ultimately affect the health benefits of the food or the anthocyanin itself.
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