Quest for a healthier grape underway

Can muscadine grapes with elevated levels of a compound already known to produce dramatic health benefits be commercially produced in Florida?

That's a question now being addressed by a Florida A&M University researcher.

After a year of preliminary work, Dr. Mehboob B. Sheikh, a professor of plant biotechnology in the Center for Vitaculture and Small Fruit Research at Florida A&M, has been awarded an $83,240 USDA specialty crop block grant administered by Florida Department of Agriculture and Consumer Services to determine the viability of commercially produced grapes with higher concentrations of resveratrol.

The specific goal of the project is "to stimulate resveratrol production in muscadine grapes to ensure health value and boost market potential."

Resveratrol is a type of natural phenol, and a phytoalexin, produced naturally by several plants - especially the roots of the Japanese knotweed, from which it is extracted commercially - when under attack by pathogens such as bacteria or fungi.

Resveratrol is also concentrated in the skins of grapes, especially red grapes.

In a number of scientific studies in recent years, resveratrol has been shown to help fight various diseases, including certain types of cancer and heart disease. It is also the key factor in the so-called "French paradox," or the scientific explanation of why French people have a lower incidence of cardiovascular disease even though they consume a diet famously rich in saturated fats. The high resveratrol content in the red wines they drink provides protection against arteriosclerosis.

As a result, commercially available resveratrol supplements have been a hot product for years and are often recommended by physicians.

Now, Sheikh and his team will spend the next two years investigating whether enhanced levels of resveratrol can be induced in muscadine grapes in Florida.

In plants, including grapes, resveratrol production is increased when the plant is stressed by factors such as bacteria or a fungus.

The key to success, Sheikh explained, is finding a stressor that can be used to boost resveratrol levels in muscadine grapes, the primary variety of grape grown in the southern regions of the U.S.

There are two basic ways to stress the plants and induce resveratrol production.

"One is to shock the plant by exposing it to external stressors," Sheikh said. "For example, we could use certain types of bacteria or fungus that are not harmful to humans. One example would be yeast. The second way is to genetically modify the plant to prompt more resveratrol production."

If successful, the innovative research could lead to new muscadine grape cultivars that could be introduced into commercial production in Florida.

The key question is whether a method can be found for inducing enough stress to artificially enhance resveratrol production to levels that could be claimed as defenses for humans and marketed accordingly.

"The goal of this research is to make sure if we say we are developing a healthier product that we are actually delivering what it is being sold as," Sheikh said. "For example, there are already products online that claim to have increased resveratrol content. But there is no proof that they contain more resveratrol."

If his work can credibly demonstrate higher resveratrol content, then winemakers could use the grapes to make wine that could be promoted for its enhanced health benefits. Or the grapes could be touted for their disease-fighting properties and sold directly to consumers.

Despite such potentially important objectives, Liwei Gu, an assistant professor at the University of Florida/IFAS, is skeptical of the practical potential of the effort, based on his own past research.

One factor, he said, is the significant differences between muscadine grapes and the French variety known for the "French paradox."

"If you think of the French grapes as a horse, muscadine grapes are a donkey," Gu said. "They are totally different genetically. They are different in their levels of resveratrol content."

The resveratrol content in French grapes used to make red wines that contain the highest resveratrol content is very high, Gu said. "It is about five-fold more than what is in muscadine grapes. In those grapes, the level is detectable, but it is very low and very hard to quantify."

Therefore, he said, he is skeptical about whether Sheikh's work can succeed.

However, he said he agreed with part of Sheikh's basic premise.

"If you use conventional methods to stress the grapes, they will produce more resveratrol," he said. But, he added, the question is how much.

"I don't believe the grape will suddenly accumulate three times or five times the resveratrol," Gu said. "And in our studies of this approach, the additional production is minimal."

Furthermore, Gu said, the French grapes with much higher resveratrol content cannot be grown in Florida because of the winter growing season climate, which is not cold enough to sustain production of that variety.

Grapes grown in cooler climates have a higher concentration of resveratrol.

Sheikh acknowledged that he is not yet certain whether his work can lead to a commercial

breakthrough, but said he is hopeful.

And given the market potential based on the established benefits and popularity of resveratrol, he said, he intends to definitively answer the question of whether a new variety of grape can be produced in Florida or not.

"And that is a long-term process," he said.