Chicken Keel Yield

black and white drawing of chicken

Feeling a little stiff today? Every day? You're not alone. Twenty million adults in the United States—half of them under age 65—suffer from osteoarthritis, pain and stiffness that occurs with the loss of joint cartilage, whether from injury or from age. Without a cartilage cushion, bones rub up against one another, causing friction that inhibits movement and ends in inflammation.

Physicians usually recommend aspirin or ibuprofen for the pain. Unfortunately, these drugs can irritate the digestive tract, resulting in anything from mild stomach ache to peptic ulcers. In search of a gentler alternative, Penn State graduate student Xin Luo is experimenting with chicken keels.

If you've ever boiled or roasted a whole chicken, you'll recognize the keel—it's the flexible wedge of cartilage connecting a chicken's breast muscles at the tip of the breastbone. According to Luo's adviser, professor of avian biology Roland Leach, chicken keels could be a good source of chondroitin sulfate, a compound present in cartilage. When taken as a dietary supplement, chondroitin sulfate seems to block the enzymes that cause cartilage to deteriorate, although researchers are uncertain exactly how it does so. When combined with glucosamine, another component of connective tissue, Luo says, it may even stimulate cartilage regrowth. And these supplements produce no apparent side effects; some research indicates that chondroitin sulfate may even ease the digestive discomfort caused by traditional painkillers.

In recent clinical trials at eight U.S. sites, a majority of patients who were given chondroitin sulfate and glucosamine for four to six weeks experienced "noticeable improvement" in joint function, Leach says. To test these results, the National Institutes of Health have organized a larger, four-year study.

If the NIH study confirms a beneficial effect, demand for chondroitin sulfate will most likely jump, Leach says. Enthusiastic supporters of chondroitin sulfate face one hitch, however: where to get the stuff. Much of the current supply is extracted either from shark cartilage or from the tracheal tissue of cows. Irresponsible shark-harvesting practices have raised protests among scientists and environmentalists, he notes; and public fear of bovine spongiform encephalopathy (mad cow disease) has left many people wary of any product originating from cows.

Where will manufacturers turn for a safe, reliable source of the compound? To chicken keels, says Leach. His experience with keel cartilage goes back 40 years, to his doctoral research at Cornell University. At the time, Leach explains, he was investigating the role of manganese in chickens' health. He was fascinated by the fact, he says, that "If you remove this tiny amount of manganese from their diet, chickens are crippled." The reason, he found, was that without manganese, chickens cannot form chondroitin sulfate. And without chondroitin sulfate, they can't build cartilage. When today's researchers began looking for new sources of chondroitin sulfate, Leach says, "I was well aware that there was a piece of cartilage that could go for this."

Except in the case of chicken sold whole, keel cartilage—along with the rest of the chicken's "rack"—remains at the processing plant, to be ground up with bones and other unappetizing bits into meal for pet food or fertilizer. If keel cartilage were a significant source of chondroitin sulfate, Leach says, a vast new market could open up for the poultry industry.

But how much chondroitin sulfate does the average keel contain? To find out, Leach approached Gary Fosmire, assistant professor of nutrition science, and Luo. Using keel cartilage from University-raised chickens, Luo developed a method to isolate the compound.

In the body, Leach says, cartilage exists as a gel, formed by proteoglycans (compound molecules of chondroitin sulfate and protein) and water. Luo's first task was to break down that gel with magnesium chloride, or road salt, which separates the proteoglycans from the water. Next, she put that solution through dialysis, to remove the salt, and freeze-dried the proteoglycans to extract the remaining water. To break down the proteins connecting the chondroitin sulfate molecules, she applied papain, an enzyme commonly used as a meat tenderizer. Ethanol precipitation caused the chondroitin sulfate to settle out of that solution, so that Luo could finally isolate it using a centrifuge. After again freeze-drying the remaining product, she weighed it and tested its purity.

Her results were encouraging. The process yielded approximately 168 milligrams of chondroitin sulfate per gram of freeze-dried cartilage, about 66 milligrams per keel. Even better, Luo's product was 75.5 percent pure, which is comparable to industry standards. With this kind of yield, Leach estimates, an average breast-processing plant—which butchers nearly 26 million chickens annually—disposes of enough keel cartilage to keep nearly 4,000 people in chondroitin sulfate supplements for a year.

In addition to being effective, Luo's process was relatively efficient. "The entire process takes eleven to twelve days," Luo says, "and except for freeze-drying, it is performed at room temperature," which eliminates the cost of creating a controlled environment. Because of its simplicity, chondroitin sulfate manufacturers could easily adapt Luo's process to their current methods of extraction, says Leach. "I have no doubt that this could be a success," he adds. "We just need someone to pick it up and run with it."

Xin Luo graduated in August 2001 with a master's of science in nutrition. Her advisers were Roland Leach, Ph.D., professor of avian biology in the College of Agricultural Sciences, 205 Henning Bldg., University Park, PA 16802; 814-865-5082; lnr@psu.edu; and Gary Fosmire, Ph.D., associate professor of nutrition science in the College of Health and Human Development, 126 Henderson Bldg. South, University Park, PA 16802; 814-863-2915; gjf5@psu.edu. Luo's work was funded by the Pennsylvania Poultry Industry Research Check-Off Program, with assistance from the Department of Poultry Science.

Last Updated January 01, 2002