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Heat-processing soybeans for ruminants.

To roast, or not to roast, hasn't been the question. Instead, soybean processors in the nation's leading dairy state have wanted to know how long--and at what temperature--to roast soybeans, to gain the most nutritional benefit for dairy cows.

Answering those questions has been a goal of ARS scientists at the U.S. Dairy Forage Research Center in Madison, Wisconsin.

Under the direction of Larry D. Satter, the researchers have demonstrated the benefit of feeding properly heated soybeans to dairy cows. The payoff has been to the state's soybean producers, who have almost doubled their acreage in the last 3 years, partly in response to the new market developing for their soybeans.

"Feeding roasted whole soybeans is becoming increasingly popular among dairy producers who want to supplement their cows' diet with a palatable protein and energy source," Satter says.

Soybeans are a good source of concentrated calories for lactating cows because of their oil content. Soybeans also contain a large amount of protein rich in lysine, an essential amino acid needed by dairy cows to make milk.

That's good news for dairy producers because a cow's digestive system can be a big protein waster. Bacteria in the rumen--the first compartment in the four-part stomach--break down protein, as well as make it. But the bacteria often break down more protein than they make, resulting in a costly waste.

"The challenge is to get feed protein to bypass, or resist, breakdown and be available later for absorption in the small intestine," says Satter.

Heating soybeans has been shown to increase the amount of bypass protein.

But dairy farmers, who may pay from $50 to $70 more a ton for roasted soybeans, don't always get their money's worth because of improper roasting methods. It's been common in the past for processors to underheat soybeans, because information on how much heat to use hasn't been available.

And while underheating fails to convert the protein in the soybean seed to bypass protein, too much heat makes the protein largely unavailable. "Either way, cows are nutritionally robbed and producers throw money away on roasted beans that are no better than raw soybeans," Satter says.

About 6 years ago, he and co-researchers at the center began exploring what happens when soybeans are roasted. They wanted to know how much heat is really needed.

So they tested soybeans heated to varying extents for bypass protein and for the amount of lysine that would be nutritionally available in the small intestine. Their experiments involved rumen bacteria, young rats, and lactating cows.

They found the best treatment to be heating beans to 295 degrees F and holding them for 30 minutes before cooling.

Maintaining that temperature for one-half hour lets the heat penetrate the beans. It also allows enough time for the protein to react with sugar to form a complex that's more resistant to rumen breakdown.

But the real proof of the cooking came when the researchers fed properly roasted soybeans to more than 100 Holsteins; they gave from 3 to 5 pounds more milk per cow daily.

Taking the work one step further, the researchers began developing a standard that could be used to show how well soybeans had been roasted. They used as a baseline a test known to the soybean meal industry as the protein dispersibility index, or PDI, which was calibrated to animal feeding experiments.

The research showed that a PDI value of 9 to 11 indicates optimum roasting for bypass protein development. Higher values are indicative of suboptimal processing.

The PDI index is being used by Dairyland Laboratories in Arcadia, Wisconsin, and whole-bean processors now have a standardized means for measuring product quality.

To round out this work, agricultural engineers Richard G, Koegel and Timothy J. Kraus are building a better soybean roaster. This machine is expected to be less costly and more energy efficient than roasters currently available.--By Linda Cooke, ARS.

Larry D. Satter, Richard G. Koegel, and Timothy J. Kraus are located at the USDA-ARS U.S. Dairy Forage Research Center, 1925 Linden Drive West, Madison, WI 53706; phone (608) 263-2030, fax (608) 264-5275.
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Author:Cooke, Linda
Publication:Agricultural Research
Date:Nov 1, 1993
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