School of Food Science

Good to The Last Drop: From Wine Grapes to Granola Bars

April 2013 | Voice of the Vine, by Rachel Webber

GenaMcKahanThe remains of wine grapes picked and pressed typically return to fields as fertilizers, but scientists are also finding ways to recycle those edible remains into healthy foods.

Take Gena McKahan’s gluten-free, merlot grape-seed flour granola bar, for example. As a food science undergraduate at Washington State University, McKahan was curious how different amounts of merlot grape-seed flour would change a granola bar’s antioxidant content when baked with other ingredients. About half the antioxidants in grapes are found in the pomace—the pulpy pile of skins, seeds, and stems leftover from winemaking—and have been shown to help prevent some cancers and cardiovascular diseases.

McKahan made granola bars using a variety of percentages of grape-pomace flour and, overall, her data analysis showed an increase in antioxidant content as the amount of grape-seed flour increased.

“I worked in health care for seven years as an ER tech, so I have seen a lot of people with diabetes and Celiac disease,” McKahan said. She believes developing functional foods (foods with added nutritional value) can help an increasingly gluten-sensitive and diabetic population more easily and accessibly meet their dietary needs.

Gena McKahan's research - grape flour“Gluten-free products and antioxidants are also part of the health trend,” McKahan said. “The population is looking at labels.”

Even if a granola or snack bar is nutritious, whether or not consumers will eat it depends largely on taste—an especially pertinent concern since wine flours tend to be more astringent, or bitter, McKahan said. In addition to grape-seed flour, the granola bar included buckwheat, rice, teff seed, and potato starch flavor. Overall, a consumer panel of 60 people said they preferred the granola bars containing 0 and 5% grape pomace flour in comparison to bars with 10 and 15%.

The research also confirms WSU sensory analyst Carolyn Ross and researcher Maria Rosales’ previous study, published in the Journal of Sensory Sciences, which suggested a granola bar with less grape-seed flour still had higher than zero antioxidant content and could be marketable. In their recipe, Ross and Rosales included sunflower seeds, another rich source of antioxidants. McKahan omitted sunflower seeds in her analysis confirming grape-seed flour on its own provides a supply of antioxidants when baked.

Eric Leber, co-owner and president of AprèsVin (French for “After Wine”) donated merlot flour for the experiments. He’s an advocate of using the whole grape. After a winemaker is done with the grapes, the seeds can be pressed for oil and then ground into flour. Leber expresses gratitude for the partnership with WSU researchers and says those in the grape-seed flour industry can use the information to inform their customers about how to best use the flours when baking.

“Using grape pomace is all about sustainability which is important in developing a viable wine industry from both a business and environmental standpoint,” he said. “It’s just a win-win-win.”

And with 8 million tons of grape pomace produced annually worldwide, there’s plenty of research material to go around.

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