Researchers at the US government-backed Meat Animal Research Center (MARC) discovered that the enzyme µ-calpaina and the variation of the protein calpastatin, both have a major impact on meat tenderness.
Calpastatin determines how much calpain is active and how tender the steak will be.
Lead researcher Mohammad Koohmaraie said his group wanted to find out why some meats become more tender while others stay too tough.
First, through protein chemistry and electron microscopy, they found that µ-calpain breaks down muscle proteins, making meat tender.
"The most significant part of this project was learning that it's calpastatin-not calpain-which controls tenderness," says Koohmaraie.
Because the calpain enzyme requires calcium for this activity, Koohmaraie and Wheeler developed a way of injecting calcium into meat to help the tenderisation process along.
"This marination technique could be used to produce meat that has both improved tenderness and juiciness," say the researchers.
Since this discovery, other researchers have confirmed that the calpastatin system influences how tender steaks are. But attempts to develop a tenderness classification system based on calpastatin activity have not been successful. This is because calpastatin explains just 45 per cent of the variation in tenderness, which is not high enough for accurate classification.
Koohmaraie's collaborators at MARC, chemist Timothy P.L. Smith and geneticist Eduardo Casas, have taken a complementary genetic approach to studying the µ-calpain system.
The US agricultural research service (ARS) reports that the scientists used a large population of crossbred cattle to identify genes influencing tenderness. They found that variation in the gene that produces µ-calpain appears to affect tenderisation.
"We're using genetics to identify DNA markers that can track variation in the calpain gene," comments Smith, "and we're looking for DNA tests that can predict the likelihood that a given animal will produce tender meat."
The researchers have sequenced the gene that produces µ-calpain in both tender and tough cattle, identifying differences that can be used as DNA markers.
Research indicates that there may be many genes other than µ-calpain and calpastatin that influence tenderness-each having a relatively small effect. The scientists warn that more genetic markers will be required to explain enough of the variation to accurately guide breeding choices.
And only about half due to genetics of the animal; the rest is the result of non-genetic, environmental factors such as stress or diet.