Research Communications

The Promise of the Pawpaw 

Can food scientists turn a native fruit into supermarket-friendly products?

By Stephanie Dutchen

The Middle East birthed the pomegranate. The Brazilian rainforest revealed the açaí berry. Will America ever lay claim to its own health-boosting superfruit?

Some have placed their bets on the pawpaw, a tropical-tasting, oblong fruit that grows wild in 26 states across the eastern half of the country, including Ohio. The pawpaw appears to boast high levels of free radical-busting antioxidants along with an array of vitamins and minerals and greater-than-average protein content.

Intrigued by the lack of research into this underutilized fruit, Ohio University food scientist Rob Brannan is putting the pawpaw to the test to find out exactly what antioxidants it contains, in what concentrations, and where. His findings could give the emerging pawpaw industry a boost- or nip in the bud any claims that it's the next cure for aging.

"My scientist brain won't let me use hyperbolic statements about 'superfruit' at this early stage," says Brannan, an associate professor and graduate coordinator of food and nutrition sciences. "We have to be cautious."

Robert Brannan 
Robert Brannan

"But," he adds, "right now I think it's in the ballpark."

Whether the pawpaw turns out to be a disease-fighting powerhouse or simply an interesting and nutritional fruit worth introducing more broadly, it has thrown a series of hurdles in front of Brannan and others who are trying to figure out whether it feasibly can be commercialized.

The temperamental fruit bruises easily and ripens to the point of inedibility within two to three days of being picked, making it impossible to ship long distances whole and fresh. It has a custardy texture like an avocado or banana, a flavor that's hard to articulate, and big seeds that aren't to everyone's tastes. Pawpaws growing on the same tree don't mature at the same time, frustrating harvesters, producers, and researchers alike. And there are upwards of 80 varieties, each of which may have different flavors, nutrient levels, seed quantities, and other characteristics.

And those are only a few of the challenges.

Working with farmers, engineers, plant biologists, agricultural scientists, and entrepreneurs across Ohio and beyond, Brannan is exploring several potential avenues around the pawpaw's eccentricities, from new processing techniques to a greater understanding of the biochemistry that drives its rapid ripening.

"My primary goal now is to determine: Is it worth the effort to commercialize this thing?" he says.

The answer will help determine whether the pawpaw remains "a niche fruit that people grow in their backyards and have once a year at farmers markets" or if it will be grown and harvested in vast orchards and pushed out across the nation.

The first step, he says, is to establish its nutritional content.

An inglorious introduction

Brannan figures he saw his first pawpaw while he was an undergraduate at the University of Maryland, where a lab mate was working to characterize its flavor. He confesses that his first taste, wherever and whenever it happened, didn't leave a strong impression.

His reintroduction to the fruit came when he joined the staff at Ohio University in fall 2005-specifically, when his three-year-old daughter ate too much of it at that year's Pawpaw Festival and threw up on the ride home. He did some reading and discovered that a pharmaceutical company in the late 1800s had sold pawpaw seed extract as a natural emetic.

As he read, Brannan was surprised to find that a lot of questions about the pawpaw weren't being asked-and that he had the capacity to answer some of them.

"It's amazing to me that there wasn't a lot known about the fruit," he says. "And we live in Pawpaw Central." (Ohio named the pawpaw its state fruit in 2009.)

Brannan didn't specialize in fruit research at the time. Instead, he was "a meat guy" with a background in the meat industry and as a chef. But there was a connection between the two: antioxidants. Among other work, Brannan has published several papers on the use of antioxidant-rich grapeseed extract in chicken products.

Brannan followed the antioxidant trail over to the pawpaw and got to work. Since then, Brannan-who may be the only food scientist in the United States studying the pawpaw-has published his research in peer-reviewed food science journals and presented his findings at events such as the International Pawpaw Conference in Kentucky and the Institute of Food Technologists annual meeting. In 2011, he was elected president of the National Pawpaw Foundation.

"It's taken me down a very interesting path that I'm glad opened up," he says. "There's such fertile ground for exploration."

 pawpaw illustration
Illustration: Alix Northrup

Antioxidant power

Previous work established the pawpaw's basic nutritional value-it's packed with vitamin C, potassium, niacin, calcium, phosphorous, magnesium, iron, zinc, copper, and manganese-and the presence of antioxidants, which have a plethora of potential health benefits.

"To discover that a fruit contains antioxidants is unremarkable. Anything that's living is going to contain them," Brannan says. "The question is, what are the antioxidants, where are they, and at what levels."

The Food Science Lab he runs at Ohio University allows him and his students to conduct chemical and physical analyses of foods. For his initial studies, he used "some crude methods" to detect levels of phenolics (chemical compounds that include antioxidants) and flavonoids, a subset of antioxidants that give fruits and vegetables their colors, in various parts of the pawpaw. 

Those studies suggest the pawpaw's total phenolic content is comparable to those of a mango, pear, or pineapple. The flavonoids-which are "the best ones" from a scientific point of view, says Brannan-might be 1/500th of that total.

But how much of those potential health benefits get passed along to a pawpaw eater depends on a few factors, such as where in the fruit the flavonoids are found. If further studies show that they're mostly concentrated in the pawpaw's seeds, for instance, that doesn't do pawpaw fans any good, because only the pulp gets eaten. However, there would be potential in processing the seeds and adding the result to other products as a nutritional value booster, Brannan says-as processors do with pomegranates. Most of the flavonoids are found in the skin, not in the edible seeds, but people are able to reap the rewards when they drink pomegranate juice, which incorporates the processed skin.

(Pawpaw juice is a less likely possibility because, as Brannan explains, "If a big company were to get behind the pawpaw, the amount they'd want just for initial testing"-about 2,000 pounds-"would probably be most if not all of a crop." If horticulturalists wanted to grow more pawpaw trees to increase yield, they'd still have to wait the five to seven years it takes for a newly planted tree to fruit.)

Nutritional value also depend on ripeness: Brannan has found that levels of phenolics, flavonoids, vitamin C, and other substances vary in underripe, ripe, and overripe pawpaw pulp and seeds.

This fall, Brannan is sending pawpaws to a tropical fruit expert in Texas to determine the precise composition of their phenolics. Once the test results start rolling in, "we can start figuring this stuff out, like what happens to the phenolics as the pawpaw ripens or when we use different heating, freezing, and storage methods," he says.

Ripe for analysis

Even if the pawpaw turns out to be a superfruit, producers still will have to overcome a significant challenge: Controlling the fruit's swift ripening. With Ohio University plant biologist Ahmed Faik, Brannan is looking at the pawpaw's cell walls-thick microscopic structures whose varying biochemistry makes bananas squishy and apples crunchy-to discover why the fruit doesn't stay fresh very long.

Specifically, they're looking at substances in the cell walls that cause softening. They start by measuring baseline levels of carbohydrates and certain enzymes right when the fruit is picked. Then they study how the cell-wall composition changes during storage in a refrigerator for up to 45 days. 

"Once we get a handle on the composition, then we can figure out some strategy to slow down the ripening," Brannan says.

The team also is studying how cell wall composition might differ among pawpaw varieties and whether it's affected by certain processing techniques.

That's because another of Brannan's recent collaborations is exploring high-pressure processing as another potential way to get fresh pawpaw pulp to market. High-pressure processing makes possible the attractively green guacamole and shrink-wrapped avocado halves in your local grocery. Brannan hopes the new technology will work for pawpaws, too, by inactivating enzymes that cause the fruit to brown and soften.

Brannan first tested the concept in fall 2011 in a partnership with Ohio State University. This year Brannan is expanding these high-processing studies with the Sandridge Food Corporation, a Medina, Ohio, company that currently works with the university's food service operation. While the studies at Ohio State examined only two varieties of pawpaw, Brannan will work with Sandridge to test a dozen varieties.

When the pawpaw are ripened to a certain maturity to withstand the process, the fruit is harvested and driven to Sandridge, where it is processed. 

Once they extricated the fruit pulp, researchers put it into a container in the processing machine that shoots pressure up to 87,000 pounds per square inch (psi). For comparison, the average pressure for commercial canning, which uses steam, is around 30 psi. 

The processed pulp is returned to Brannan's lab, where it will be analyzed over several months to monitor the effect of physical and chemical changes caused by processing on product quality. 

"If high-pressure processing reduces the enzyme that causes rapid browning, then quality is improved," says Brannan. "If it reduces cell wall enzymes, then texture is improved because the fruit is less mushy. If it reduces flavonoid or flavor compounds, then quality is not improved because important nutrients or flavors are destroyed."

Although Brannan does not monitor the presence of microorganisms, "There are a lot of factors that go into the word 'quality,'" he explains. "Safety is first among them."

If the research continues to go well, the process could yield a marketable product in a few years, which could be the impetus for growers to form a collective to produce enough fruit to sell profitably, Brannan says.

 pawpaw illustration
Illustration: Alix Northrup

Finding a market

But that raises perhaps the most significant question: If you bring the pawpaw to market, will people want to eat it?

Before Brannan arrived on campus, former Ohio University nutritionist Melani Duffrin performed flavor analyses using student groups and conducted informal consumer opinion tests using baked goods (think pawpaw muffins). Her efforts began to build a vocabulary for describing the pawpaw's flavors and textures.

"People need a vocabulary to help them become familiar with the flavors," says Brannan. Building on Duffrin's work, he and his students examine the relationship between human perception and instrumental analysis of food in the Sensory Analysis Lab. In February 2012, he co-authored a paper in the Journal of Food Research that gave a detailed nutritional analysis of that purée and introduced a standardized pawpaw sensory lexicon.

Ohio University alumnus Chris Chmiel doesn't want to wait for lexicons or mass production. Co-owner of Integration Acres, an Ohio-based business that bills itself as the world's largest pawpaw processor and supplier, as well as the founder of the Ohio Pawpaw Festival and the Ohio Pawpaw Growers Association, he is already commercializing and popularizing pawpaws-and finding a ready consumer base.

He's made a brisk business in online sales of not only frozen purée but also jars of pawpaw chutney, jam, relish, and vinaigrette. The annual festival, held in Albany and now in its fourteenth year, draws crowds with its pawpaw microbrew beer, Popsicles, smoothies, guacamole, pies, and other creations.

In contrast to most other pawpaw growers, including a 2,000-tree cultivated orchard at Kentucky State University, Chmiel harvests his fruit directly from wild trees.

Having watched whole pawpaws rot rapidly on the ground at his company's start 16 years ago, Chmiel agrees that processing is the key. Frozen pulp can be kept bright yellow-orange by adding vitamin C. If Brannan's research yields shelf-stable pulp, producers like Chmiel can stock supermarket shelves long after pawpaw season is over.

"People are used to having stuff year-round, unless they go to farmers markets," Chmiel says.

Consumers aren't the only targets: Companies looking to market niche products, such as pawpaw beer, also have shown interest in pawpaw pulp, he says.

As a preview of what national or worldwide pawpaw production could be, Chmielís is a success story.

"We've been able to sell everything we've produced," he says. "It shows people there's interest and we can have a market."

The fruit's future

While Brannan continues his nutrition and processing studies, other U.S. pawpaw researchers are pursuing work in horticulture, agriculture, and possible medical applications (compounds in the fruit's seeds and bark may fight certain cancers).

"The food science research and the agriculture/horticulture research go hand-in-glove," says Brannan, who already coordinates with Ohio growers associations and has been trying to form partnerships with the team at Kentucky State. 

"If the food scientists can show that we can extend pawpaw shelf life to make it commercially viable, then it is up to the others to produce varieties of pawpaw that look and taste good, have good texture, are nutritionally superior (low fat, high antioxidants, etc.), and take advantage of the horticultural things that matter, like producing big fruit with few or small seeds, reduced time to produce fruit, and a multitude of harvest issues."

However, there is no guarantee of success. In these early stages, researchers are finding it hard just to secure enough funding. Brannan was fortunate to earn a grant from Ohio University to pursue the high-pressure processing work.

"Right now we're little groups reaching into the couch cushions for research money and hoping to turn federal heads with the preliminary results," he says. "That's when it will go from zero to 60."

He jokes that the pawpaw could use a patron like the private citizen in California who provided significant funding to generate preliminary research results demonstrating the potential health benefits of the pomegranate.

If the pawpaw remains fundable, "I can't imagine that over the next five to ten years I'm going to stop working on this," says Brannan. 

If so, it's possible that the fruit that nourished Native Americans, sustained Lewis and Clark, and graced the tables of Thomas Jefferson and George Washington could stage a modern-day comeback.

"The pawpaw has an all-American story-red, white, and blue," says Brannan. "If there's an American superfruit, it would be the pawpaw. If we can back up the story with the product, it can be powerful."

The article was published in the Autumn/Winter 2012 issue of Ohio University's Perspectives magazine.