Toward More Tender Beef
Cuts of beef are injected with a solution of food-grade calcium
chloride by physiologist Mohammad Koohmaraie (right) and food technologists
Steven Shackelford (center) and Tommy Wheeler.
Shopping at a supermarket meat counter stocked with fine-textured, firm,
bright-red steaks, you want to pick one that will cook up really tender. Your
best guess is to take one that's well marbled with tiny flecks of fat.
For today's savvy shoppers, marbling is the only indicator of tenderness.
But with tomorrow's technologies, less knowledgeable consumers may be more
confident of choosing beef that is tender and tasty.
ARS researchers hope in the next 10 years to advance the science of breeding
animals so that such meat is reliably classified and consistently available.
Because tenderness of beef is not highly predictable and is known for sure
only when the meat is eaten, it has been identified as one of the hottest
topics in the livestock and meat industry, says Dan Laster, director at the
Roman L. Hruska U.S. Meat Animal Research Center (MARC) in Clay Center,
But marbling accounts for only about 10 percent of the variation in meat
tenderness, says animal physiologist Mohammad Koohmaraie, head of the center's
Meats Research Unit. From among many other positive and negative influences on
tenderness, he and his colleagues have found an enzyme-inhibiting protein
called calpastatin that accounts for another 44 percent of the variation in
tenderness of aged beef.
Depending on cattle's genetic makeup, different levels of calpastatin exist
in the meat and contribute to toughness by inhibiting an
enzymecalpainin the postmortem aging, or tenderizing process.
"Beef tenderness or toughness, controlled about 70 percent by
environment and 30 percent by heredity, may involve expression of many
genes," says Koohmaraie.
Because each gene's contribution is minor compared to confounding
environmental factors, identifying desired gene combinations would be almost
impossible through classical inheritance studieslike "looking for a
needle in a haystack." But ferreting out the genetics is just the kind of
task that may be doable, with refinement of the world's first cattle genome map
that was recently published by a 12-member MARC research team.
Scientists of the gene mapping group and the Meats Research Unit have found
various forms of a gene for calpastatin on chromosome 7 of the beef genome and
have developed diagnostic probes for them. The idea is to use such probes--DNA
fragments that bind to a specific form of genetic materialto tell whether
an undesirable gene is possessed by an individual animal, group, or family of
animals. Researchers may know within 3 years how well calpastatin probes will
work in the quest for tender beef.
But defining future strategies to produce beef of the best eating quality
will involve much more than detecting calpastatin genes, Koohmaraie says. Just
as tenderness is not the only influence on palatability, calpastatin is not the
only factor affecting tenderness. However, calpastatin explains more of the
variation in tenderness than does any other trait.
A project is now under way at MARC to identify chromosomal regions that are
associated with differences in beef tenderness. Successful completion of this
project will allow selection for tender beef prior to slaughter.
Someday, calpastatin in beef may be measured routinely as part of a quality
classification system that would lend itself to marketing of branded products
of predictable quality. Koohmaraie and his colleagues are trying to develop
such a measurement test.
Physiologists Mohammad Koohmaraie (left) and Matthew Doumit
examine purification results on calpastatin, an enzyme-inhibiting protein that
accounts for 44 percent of the variation in tenderness of aged beef.
The classification system may even evolve to include tests on live cattle
before marketing. Carcasses from cattle rated unacceptably tough in
calpastatin-based or marker-assisted tenderness scores might be targeted for
special treatment such as calcium-activated tenderization.
The technologies may help those cattle breeders who are faced with about the
same degree of genetic variation within breeds as between breeds for many
traits, says Larry V. Cundiff, a MARC animal geneticist.
Cattle of mostly Bos indicus breed ancestryvalued for their
heat tolerance, reproductive abilities, and the hybrid vigor they contribute to
crossbreeding programsare more likely than their Bos taurus
counterparts to produce tough beef. "When we can identify desirable genes
in individual animals, we can more freely use breeds for the traits they bring
to a crossbreeding system," Cundiff says.
In a study of meat from 555 steersmostly crossbreds but including 9
purebred linesARS food technologist Steven D. Shackelford and his
colleagues at MARC concluded that breeding for low levels of calpastatin may be
one of the routes to tender beef.
They studied heritabilities of traits and also took into account the
associationsstatistical correlationsbetween calpastatin activity
and intramuscular fat, tenderness, retail product yield, and average daily
Generally, animals with desirably low levels of calpastatin yielded more
lean meat per pound of carcass than did animals with desirably high levels of
If genetic markers prove to be an indicator of beef tenderness and
palatability, says Laster, marbling may come to be regarded as a less important
factor in predicting eating quality. So, many cattle in the future may not be
fed as long on large amounts of the grain and concentrated feed supplements
required to meet today's quality grade standards.
An extra pound of gainlargely faton a 1,200-pound animal often
requires about 40 percent more feedmostly grainthan a pound of gain
on a leaner 1,100-pound animal. And much excess fat at the edge of heavily
marbled cuts is routinely trimmed away.
That means that when consumers can be reliably assured that beef is tender,
though not heavily marbled, the beef industry will be able to provide a leaner
product at less cost.
In addition to the calpastatin work, Koohmaraie and his colleagues have also
found that injecting a controlled amount of calcium chloride solution into meat
anytime after slaughter enhances meat tenderness.
The current protocol for Calcium-Activated Tenderization (CAT) calls for
injecting cuts of meat with up to 5 percent, by weight, of a 2.2 percent
food-grade calcium chloride solution and then vacuum packaging and storing them
for 7 days before consumption.
Calpain enzymes, activated by the calcium chloride solution, tenderize tough
beef by breaking apart a ropelike protein called desmin that holds strands of
muscle fiber together.
"The calpains degrade themselves at the same time they degrade muscle
proteins," says Koohmaraie.
The process is effective in all muscle at any time after slaughter,
regardless of livestock species, breed, or gender. And the injected calcium
chloride activates the calpains without overtenderizing the meat.
Calcium chloride injection, which is similar to the process used for many
years by the meat industry to inject water and curing ingredients into hams,
has received federal regulatory approval. But appropriate labeling of the meat
products is required before a company can sell them.
Besides improving tenderness, the calcium chloride solution gives beef a
calcium content about half that of milk, with no adverse effect on the meat's
color or shelf life, Koohmaraie says. And according to MARC food technologist
Tommy L. Wheeler, consumer tests indicate both restaurant and supermarket
consumers prefer calcium-injected beef because of its improved tenderness.
By Ben Hardin, ARS.
Scientists mentioned in this article are at the
L. Hruska U.S. Meat Animal Research Center, P.O. Box 166, State Spur 18D,
Clay Center. NE 68933; phone (402) 762-4109.
"Toward More Tender Beef" was published in the
March 1995 issue of
Agricultural Research magazine.