Salam Ibrahim, Ph.D., and his research partner Tahl Zimmerman, both faculty in the Department of Family and Consumer Sciences, are seeking to find ways to use sweet potato byproducts to culture strains of the bacteria that cause fermentation, a necessary ingredient for yogurt production.

Five to ten thousand years ago, when the first cow, goat or sheep herders in Mesopotamia discovered that they could not only eat the fermented milk that their warm climate had produced, but that they could make it tasty, the culinary world gained an asset: yogurt was born.

This ancient food, thought to have been eaten as long as milk-producing animals have been domesticated, not only enabled milk to be preserved through fermentation, which turns it into yogurt or cheese. It also proved to have numerous health benefits as an excellent source of protein, calcium and probiotics.

By the 20th century, yogurt had hit the big time, having migrated to Europe with travelers from Arabia, Turkey, India and Russia in the Middle Ages, then gone around the world as both a creamy, fruity breakfast and snack essential and a nutritious cooking staple. The purpose of the fermentation process that creates yogurt had turned from simply preserving the milk product, to selling it.

Food scientist Salam Ibrahim, Ph.D., in the Department of Family and Consumer Sciences, has researched yogurt and its benefits for the past 22 years, and has witnessed much of yogurt’s progression from niche health food to dairy aisle powerhouse. Within this evolution, he has seen issues arise for the industry.

“Selling yogurt in commercial production calls for consistency,” he said. “Consistency is the key to making a product acceptable to consumers. Modern yogurt production involves culturing milk with live bacteria, which produce lactic acid, which coagulates the milk proteins and makes the milk ferment. That cultured bacteria must be grown in the same way, every time.”

That consistency starts with a reliable, nutritious, inexpensive media in which to grow Lactobacillus bulgaricus and other forms of lactic acid-producing bacteria that cause fermentation. A quality medium provides the consistency to give producers control of their final product. But therein lies the problem: although many media, including milk, whey and soy, have been used through the years, in the modern era, they are all either too expensive or too allergen-producing to be ideal for commercial production.

In the industry’s conundrum, Ibrahim sees an opportunity to boost both the product’s health benefits and North Carolina’s economy. He and his research partner, Tahl Zimmerman, have developed a patent-pending process of growing Lactobacillus bulgaricus, one of the bacteria that cause fermentation, in a media made from byproducts of the sweet potato.

“In industry, cultured bacteria has been grown in the same way for years: in a media that can be carefully controlled, called the “mother.” For years, that media was milk, and as long as milk’s cost was low, that was fine,” Ibrahim said.

“In the 1980s, milk prices started to rise, and the industry started looking for alternatives. It settled on whey, a byproduct of milk. But by the 1990s, healthy bacteria called probiotics had become popular food additives, and so the industry no longer had to simply culture bacteria for cheese and yogurt. It needed to grow bacteria in such a way as to grow a high cell mass of viable cultures for the consumer to get the optimal health benefit. In addition, the cells had to have high enzymatic activity to stay alive a long time to get to market. All of these factors became challenges to maintaining good products.”

Even as the industry has moved forward, many challenges have remained, Ibrahim said, and the 20-year quest for an alternative media has been his focus.

“In order to grow good bacteria, you have to have three nutrients: a nitrogen source, a carbon source and a buffer, such as a phosphate, to make sure they reach a high cell number,” he said. “We worked with several things through the years. But then, I thought of the sweet potato.”

High in nutrients, low in calories, this popular tuber is North Carolina’s top crop and official vegetable. In 2019, N.C. grew nearly 2 billion pounds of sweet potatoes which brought nearly $375 million to the state economy, according the U.S. Department of Agriculture. In fact, the Tarheel state accounts for 50 percent of the national supply and grows more than 95,000 acres a year, nearly 30,000 more than the next closest growers, California and Mississippi.

“We have a lot of sweet potatoes – so many that 20 percent are left in the field as being damaged, irregular in shape, or too small,” he said. “Also, when sweet potatoes are processed, byproducts are created, such as the peel or the ends. But these are all high in potassium, nitrogen, calcium, phosphorus and the micronutrients essential to bacteria growth. That caught my attention.

“I thought, what if we could extract nutrients from sweet potato byproducts and create a low-cost, water-based liquid that could be used as a medium for growing Lactobacillus bulgaricus and other beneficial bacteria that could be used as probiotics or supplements for other foods?”

Ibrahim and Zimmerman have been working with the food industry for several years, and the work has been successful. The liquid media that they have created from sweet potato byproducts has proved to not only grow high numbers of bacteria, but to grow faster-replicating, longer-surviving, better functioning bacteria that can be used as probiotics, they said.

“There are alternatives out there now, but they’re not so good,” Zimmerman said. “Past efforts to create such a media in a sustainable way have ultimately failed because they invariably rely on expensive chemical or enzymatic processes that require a high amount of energy from the grower. Our technology is a purely mechanical process that requires few other inputs, and it supports more viable cells, better.”

The rise of consumer demand for probiotics, or beneficial bacteria, as food supplements has produced its own challenges for the food industry. These high-functioning bacteria must not only grow well, but also have long shelf lives so that consumers get their full benefit.

“The probiotics industry uses bacteria as medicine,” he said. “One problem they’ve had is that an animal product-based media, such as whey, and the familiar vegan substitute soy, each have the potential to be an allergen. A sweet-potato media is plant-based and can be marketed as vegan, but doesn’t have the allergenic potential.”

Working with the Office of Intellectual Property Development at N.C. A&T, Ibrahim and Zimmerman have applied to patent their process, which can benefit both farmers and industry.

“Adopting this technology would mean that farmers could find another market for their discarded goods, food processors could use sweet potato byproducts that are now discarded, and the industry, which is searching for new technologies, could manufacture plant-based probiotics in a sustainable, affordable way,” Zimmerman said.

Ibrahim and Zimmerman have obtained a two-year, $50,000 grant from the National Science Foundation to work with potential industry partners on their needs and interest in the new media, as well as to further their research and production efforts. Their collaborative efforts are beginning to pay off with interest from the industry, Ibrahim said.

“The yogurt industry has a problem. We think we have an answer for them,” Ibrahim said. “The basic research is over; now we’re designing the equipment and working with partners’ particular needs. We’re very excited. Anything is possible.”