Researchers separate spent brewer’s grain into proteins with potential food applications

07 Apr 2021 --- Scientists are reporting a new way to extract the protein and fiber from brewer’s spent grain and use it to create new types of protein sources. Homebrewing enthusiasts and major manufacturers experience the same result of the beer-making process: mounds of leftover grain. Once all the flavor has been extracted from barley and other grains, what’s left is a protein-rich and fiber-rich powder typically used in cattle feed or discarded in landfills. 

The researchers have presented their results at the spring meeting of the American Chemical Society (ACS).

“There is a critical need in the brewing industry to reduce waste,” says Haibo Huang, Ph.D., the project’s principal investigator. His team partnered with local breweries to find a way to transform leftover grain into value-added products.

“Spent grain has a very high percentage of protein compared to other agricultural waste, so our goal was to find a novel way to extract and use it,” adds Yanhong He, a graduate student. Both Huang and He are at Virginia Polytechnic and State University (Virginia Tech). 

Spent grain packed with protein and fiber
Craft brewing has become more popular than ever in the US. This increased demand has led to more production, generating a major uptick in waste material from breweries, 85 percent of which is spent grain. 

This byproduct comprises up to 30 percent protein and up to 70 percent fiber. While cows and other animals may digest spent grain, it is difficult for humans to digest it because of its high fiber content.

To transform this waste into something more functional, Huang and He developed a novel wet milling fractionation process to separate the fiber’s protein. 

Compared to other techniques, the new process is more efficient because the researchers do not have to dry the grain first. 

They tested three commercially available enzymes –  alcalase, neutrase and pepsin –  in this process and found that alcalase treatment provided the best separation without losing significant amounts of either component. After a sieving step, the result was a protein concentrate and a fiber-rich product. 

Alternative protein sources 
Up to 83 percent of the protein in the spent grain was recaptured in the protein concentrate. Initially, the researchers proposed using the extracted protein as a cheaper, more sustainable replacement for fishmeal to feed farmed shrimp. 

However, more recently, Huang and He have started to explore using protein as an ingredient in food products, catering to the consumer demand for alternative protein sources.

However, that still left the remaining fiber-rich product without a specific use. 

Last year, Huang’s postdoctoral researcher Joshua O’Hair, Ph.D., reported finding a new species of Bacillus lichenformis in a spring at Yellowstone National Park. In the paper, they noted that the bacteria could convert various sugars to 2,3-butanediol, a compound used to make many products, such as synthetic rubber, plasticizers and 2-butanol, a fuel. 

O’Hair pretreated the extracted fiber with sulfuric acid, then broke it down into sugars from cellulose and hemicellulose. She then fed the sugars to the microbe, producing 2,3-butanediol. 

The team plans to scale up, separating the protein and fiber components to keep up with the volume of spent grain generated at breweries. 

They are also working to determine the separation process’s economic feasibility, as the enzymes currently used to separate the protein and fiber components are expensive. 

Huang and He hope to find suitable enzymes and green chemicals to make this process even more sustainable, scalable and affordable.

The researchers acknowledge support and funding from Southern Sustainable Agriculture Research and Education Graduate Student Grant, the Virginia Agricultural Council and the John Lee Pratt Graduate Scholar Program. 

Edited by Gaynor Selby

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