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Purple power

November 18, 2013  By Rosalie I. Tennison

Purple potatoes such as these have seldom been a favourite of North American consumers, but research is underway examining the antioxidant pro-perties of purple potatoes and carrots and how these vegetables can improve health beyond the benefits of white potatoes and orange carrots. Rosalie I. Tennison

Can vegetables get healthier?

There is no question that eating vegetables is a good way to minimize the risk of some cancers, maintain a healthy body weight, increase the intake of vitamins and minerals, and, generally, contribute to overall health. But, as food scientists study how the many components in vegetables can improve human life in multiple ways, they are learning that the colour also can be beneficial for human health.

Natively grown in South American countries, purple potatoes were seldom a favourite of North American consumers. The same is true of purple carrots. However, what can almost be termed “heritage varieties” remained interesting to home gardeners, who kept these vegetables from disappearing completely. Now, research is being conducted on the antioxidant properties of purple potatoes and carrots and how these vegetables can improve our health beyond the health benefits of white potatoes and orange carrots.


“Most vegetables have some antioxidant properties, but purple carrots and potatoes have more,” explains Dr. Mary Ruth McDonald, a researcher in the Department of Plant Agriculture at the University of Guelph in Ontario. “Purple carrots have more antioxidants than orange carrots and even the purple skin on the potatoes is high in antioxidants. It’s due to pigments called anthocyanins that produce the intense colour.”

Dr. McDonald and a team of other researchers, including Dr. Rong Cao of Agriculture and Agri-Food Canada and Drs. Kelly Meckling and Al Sullivan of the University of Guelph, are currently conducting research into the health benefits of purple carrots and potatoes. She believes the antioxidants in these vegetables, when consumed regularly, will reduce high blood pressure and improve the quality of life for people with Type 2 diabetes. Her study is investigating how strong an effect, if any, eating purple potatoes or carrots in comparison with eating white potatoes and orange carrots will have on subjects suffering from Type 2 diabetes, high blood pressure and other lifestyle-related health problems. Research has been completed using rats, which showed encouraging results of significant reductions in blood glucose levels when the animals ate the purple vegetables.

The research is now progressing towards working with human subjects. In the study, subjects will have to eat either purple carrots or purple potatoes every day, while the control group will eat either orange carrots or white potatoes every day.

“It’s important to see what eating these compounds does for human health,” Dr. McDonald explains. “We need to understand how the compounds are absorbed into the body.”

She expects to have some preliminary results from the study in 2014.

If Dr. McDonald proves the health benefits of the purple vegetables, there will be increased opportunities for commercial vegetable growers. At present, purple vegetables are largely the niche cornered by market gardens, the purveyors of heritage varieties, organic produce and scale farming operations. There is some commercial production of purple carrots in the Holland Marsh area of Ontario, but the yields are poor in comparison to their orange cousins. However, Dr. McDonald believes, if the health benefits are proven, an increase in breeding programs and production research will be likely.

“The purple carrots are requiring more management because the varieties we have are not well adapted to our growing conditions,” Dr. McDonald says. “There has not been a breeding focus for our production system.”

That is starting to change as breeding programs are including purple carrots and potatoes in order to have varieties available to Canadian growers once the market is developed.

If the health benefits are proven, the mainstream media will likely get on board to excite the public interest and opportunities will increase for growers. Once good varieties are available, the production system should work similarly to the present system for white potatoes or orange carrots. However, steps may need to be taken to maintain the colour of these vegetables because in some potato-growing areas sustaining the colour of red-skinned potatoes is a challenge.

Then, there is the cooking issue. Consumers will have to be educated on the best way to prepare the vegetables in order to maintain the antioxidant benefits. If the potatoes are cut, the colour leaches out into the cooking water and the antioxidants are reduced, so the best way to prepare purple potatoes is to bake them to preserve all the benefits in one tasty package. The purple pigment in the carrots and potatoes is water soluble, so baking or preparing the vegetables whole will keep their health benefits intact. Dr. McDonald also believes there is an opportunity to get children eating healthier because they may think eating purple vegetables is “cool.”

What’s next?

“We need the demand for these vegetables and then we need adapted varieties for our growing areas,” Dr. McDonald admits. “We need varieties that yield as well as a white potato or an orange carrot to make it worthwhile for growers to add them to their production plans.”

When blueberries became the fruit of choice because of their proven antioxidant properties, production soared and the fruit began to appear everywhere from the fresh counter to the juice aisle. Dr. McDonald says purple carrots are being used as a juice ingredient, but it is a specialized market, and the products are not readily available in all stores.

Nevertheless, the system is in place to make the most of the antioxidant properties of purple potatoes and carrots. The results of Dr. McDonald’s research may be the spark to get varieties developed and larger-scale production underway.

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