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Iowa State researchers improve soy processing by boosting protein and sugar yields

February 15, 2007

AMES, Iowa — Graduate student Bishnu Karki turned on an ultrasonic machine in an Iowa State University laboratory. With a loud screech, the machine's high-frequency sound waves churned a mixture of soy flakes and cold water. And that churning could be a major boost to soy processors and the food industry.

Adding ultrasonic pretreatment to soy processing boosts and improves the yield of protein that can be added to foods, said Samir Khanal, an Iowa State research assistant professor of civil, construction and environmental engineering. In Iowa State laboratory tests, exposing ground and defatted soy flakes to ultrasonics has increased the release of soy proteins by 46 percent.

Khanal said the ultrasonic treatment also breaks some of the bonds that tie sugars to the soy proteins. Separating the sugars from the proteins improves the quality of the proteins. It also boosts the sugar content of the soy whey that's left after processing. Ultrasonic treatment boosted sugar yields by 50 percent.

The low-cost, sugar-enriched whey can replace an expensive compound used to grow lactic acid bacteria, Khanal said. The bacteria produce nisin, a valuable natural food preservative that's also used in cosmetic and health care products such as mouthwash and toothpaste.

"Our preliminary economic analysis showed that the proposed technology could generate revenue up to $230 million per year from a typical plant producing 400 million pounds of soy protein isolate," says a summary of the research project. "This is a major breakthrough in the soy processing industry."

Khanal leads a research team that includes Hans van Leeuwen, an Iowa State professor of civil, construction and environmental engineering; David Grewell, an Iowa State assistant professor of agricultural and biosystems engineering; Stephanie Jung, an Iowa State assistant professor of food science and human nutrition; and Buddhi Lamsal, a senior scientist at Kansas State University in Manhattan. Larry Johnson, the director of Iowa State's Center for Crops Utilization Research, and Tony Pometto, an Iowa State professor of food science and human nutrition, are assisting the project. Iowa State graduate students Bishnu Karki, who's studying environmental science, and Debjani Mitra, who's studying biorenewable resources and technology, are also working on the research project.

The research is supported by a grant of $81,977 from the Grow Iowa Values Fund, a state economic development program. Cargill and other major food processors are supporting the research project with materials and supplies. And the Iowa Biotechnology Byproducts Consortium is supporting the nisin portion of the project with a grant of $155,711.

Khanal said the technology has boosted protein and sugar release in batch-by-batch lab tests. The researchers will now try lab tests to see how it works in the same kind of continuously flowing stream that would be used in a soy processing plant.

The researchers are optimistic the technology can be effective and efficient in a full-size soy processing plant. Van Leeuwen said the ultrasonic treatments only require a few seconds and can be done in a pipeline connecting a plant's soy processing units. He also said the capital costs and power requirements for ultrasonics are small.

Yes, Khanal said, "I think this is commercially viable."

Iowa State University