Protein facilitates meat tenderization process.

Imagine eating a tender steak. Tenderness is a very important trait to consumers. USDA-ARS scientists are looking at biochemical mechanisms that make the meat of certain cattle tender.

The researchers have found that the tenderness of meat changes during postmortem aging--first going through a toughening phase before the tenderization phase begins. Right after slaughter, meat is tender. But for the next 12 hours or so, rigor mortis takes place, stiffening the muscles and making the meat tough. Toward the end of the toughening phase, while the carcass is hanging in a cooler, the tenderization phase begins, which makes most meat, but not all, suitably tender.

Tenderization is caused by the enzyme [micro]-calpain degrading some muscle proteins. The scientists believe industry shouldn't sell meat before it has aged for 14 days because steaks are more likely to be tough. But those extra days add considerable cost to production because of the requirements for space and controlled temperatures.

Not all meat reaches the same level of tenderization. The [micro]-calpain breaks down muscle proteins, making meat tender. Because the calpain enzyme requires calcium for this activity, scientists came up with a way to inject calcium into meat to help the tenderization process along. This marination technique could be used to produce meat that has both improved tenderness and juiciness.

Although [micro]-calpain causes the protein degradation that improves tenderness, it's actually the activity of the protein calpastatin that determines how much calpain is active--and thus how tender the steak will be. But attempts to develop a tenderness classification system based on calpastatin activity have not been successful. Calpastatin accounts for just 45% of the variation in tenderness, which is not high enough for accurate classification. Researchers are using genetics to identify DNA markers that can track variation in the calpain gene. They are looking for DNA tests that can predict the likelihood that a given animal will produce tender meat.

Scientists have released a DNA test that was effective in identifying tough beef cattle. Since research indicates that there may be many genes other than [micro]-calpain and calpastatin that influence tenderness, additional genetic markers will be required to explain enough of the variation to accurately guide breeding choices.

Further information: Mohammed Koohmaraie, USDA-ARS Roman L. Hruska U.S. Meat Animal Research Center, Spur 18D, Clay Center, NE 68933; phone: [phone]; fax: [phone]; email: [e-mail].