SciTech

Scientists savor sweet potatoes

Mary Ann Lila, director of N.C. State’s Plants for Human Health Institute, at the North Carolina Research Campus, in Kannapolis, recently led research she hopes will inspire consumers to maximize sweet potatoes’ health benefits year-round.
Mary Ann Lila, director of N.C. State’s Plants for Human Health Institute, at the North Carolina Research Campus, in Kannapolis, recently led research she hopes will inspire consumers to maximize sweet potatoes’ health benefits year-round. Plants for Human Health Institute

At Thanksgiving and Christmas meals around the country, millions will say, “Pass the sweet potatoes.” But after the holidays, many people walking through their grocery store’s vegetable section instead will pass by them.

Mary Ann Lila is working to change that. The director of N.C. State’s Plants for Human Health Institute, in Kannapolis, recently led research she hopes will inspire consumers to maximize sweet potatoes’ health benefits year-round. The study’s main takeaway is that these vegetables’ functional ingredients can be incorporated into many different snack foods, baby foods, military rations and more.

“In many parts of the world – South America, Oceania and more – sweet potatoes are well recognized as health-protective, nutritious foods,” Lila said. “But in the USA, so many people miss this benefit because they only think of sweet potatoes at Thanksgiving and Christmas, served up with maple syrup and marshmallows.

“The truth is that sweet potatoes are so tremendously versatile and full of health-protective phytoactive compounds that are not appreciated by the general public.”

Phytoactives at work

North Carolina produces 40 percent of all U.S.-grown sweet potatoes, which are known for their vitamin content, low calories and high fiber. In fact, a study by the Center for Science in the Public Interest ranked the sweet potato as the most nutritious vegetable by an overwhelming margin.

Research conducted by Lila and her colleague Mary Grace (most recently published in the Journal of Food and Nutrition Sciences) involved the vegetables’ phytochemicals – naturally occurring compounds in plants that protect them from disease. When we eat a fruit or vegetable containing these phytochemicals (or phytoactives), we realize those benefits.

Lila’s lab has done comprehensive studies on three kinds of phytochemicals found in sweet potatoes: phenolic acids, which are linked to the vegetable’s antioxidants and ability to lessen dangerous free radical molecules; carotenoids, with their vitamin A, antioxidant, anticancer and heart benefits; and anthocyanins (only in purple sweet potatoes), known as anti-diabetic, neuroprotective and immune-protective agents.

Though sweet potatoes come in a rainbow of colors – orange, yellow, orange/yellow, white, red, brown, purple – all are full of phytoactives. “The orange/yellow are richest in the carotenoids, whereas the purple sweet potato uniquely has the anthocyanin pigments,” Lila said. “Purples are not as widespread as orange/yellow, but they are worth seeking out and add something distinctive to the plate.”

Focusing on sweet potato juice and sweet potato flour, Lila’s lab used a process that produces a stable, dry and powdered ingredient base. In this process, a protein-rich flour is enriched with phytoactives such as fruit polyphenols.

The fruit polyphenols are chemically bound to a ground, sweet potato flour, and purple sweet potato polyphenols are bound to other protein-rich flours. In both instances, this results in vastly increased concentrations of phenolics – compounds that have been linked to reducing the risk of cancer and possessing antioxidant effects.

Recipes for health

“Our mission now is to not just discover what compounds are healthy in fruits and vegetables, but then to go the next step on how to deliver to consumers in ways that are easy, convenient and innovative,” Lila said. So the lab also ran some tests to determine which products may be a good fit for sweet potato ingredients. A sensory evaluation panel judged the appearance, flavor and texture of six sweet potato bases, leading to recipe recommendations.

“The stable polyphenol-protein ingredients … allow the consumer to incorporate sweet potato goodness into recipes that they may not have thought of before,” Lila said. “Sweet potato flour can be complexed with health-protective polyphenols from grapes, berries, etc., and used in breads, cakes, pancakes, etc. Sweet potato juice from the purple sweet potato is a superb source of polyphenolic compounds; we complexed these with other types of edible flours to produce shelf-stable, cost-effective ingredients that add to the versatility for menu preparation.”

Shelf-stable is an important and promising part of the equation. Another research project evaluated four different varieties of sweet potatoes for their phytochemical composition at harvest, as well as after four months and eight months in storage. The study found that antioxidant and anti-inflammatory activity remained regardless of duration.

Lila says the search is on for licensing partners who’ll include these sweet potato benefits in commercially available foods. She says Carolina Wild juice, which signed a short-term contract with N.C. State, is introducing a sweet potato juice and muscadine juice product with complementary phytoactive ingredients.

Meanwhile, she says the simplest way to ensure you’re benefiting from these ingredients is surrounding yourself with color at the dinner table: “It is our brown-and-white, meat-and-potatoes pasta diet in the USA that is leading to ill health and outrageous and escalating levels of obesity and diabetes.”​

Sweet versatility

The sweet potato has many uses that are interesting – and some that are more fun.

According to a paper written by Albert E. Purcell of N.C. State’s Department of Food Science, sweet potatoes have been used as a wheat substitute in making bread in the U.S. and Israel. Japanese and Chinese scientists have fermented sweet potatoes to develop methods for producing commercial alcohol, acetone, butanol, itaconic acid and citric acid. Sweet potatoes are also fermented for alcoholic beverages such as Covington gourmet vodka, produced in rural Eastern North Carolina. They’ve even been used for wallpaper paste.

Now that you know some of the sweet potato’s uses, you may also want to know what a sweet potato is and isn’t. It’s a kind of flowering plant with tuberous roots that are a root vegetable. So you can accurately call it a plant or a vegetable.

But a sweet potato isn’t a potato. It isn’t a yam. So Covington’s trademarked slogan, “the best yam vodka on Earth,” isn’t technically accurate no matter how good the contents may taste. But some may say it’s a sweet play on words.

Reid Creager

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