Researchers at Texas Tech University and Texas A&M may have discovered a way to increase marbling in beef without increasing external fat. The researchers found that the key is isolating a receptor in marbling adipocytes, which are fat cells juxtaposed to muscle tissue. Activation of that receptor, called G-coupled Protein Receptor 43 (GPR 43), produces lipids, and lipids are the key ingredient in marbling.
“We feel if we can regulate this receptor in marbling, we can increase marbling without making the cattle fatter,” said Brad Johnson, professor in the Dept. of Animal and Food Sciences, Texas Tech. “As the cattle make fat, the feed efficiency goes down and for consumers we trim off all the excess fat. But if marbling is what consumers want, we can increase marbling at different times in the feeding cycle without making the cattle fatter, and that would be a huge benefit for the beef industry.”
Though they might look the same on a ribeye cut, there is a distinct biological difference between back fat and marbling, and it affects the palatability of beef. The key is in the composition of the adipocytes that make up the back fat and marbling. Subcutaneous adipocytes are more commonly known as back fat, and intramuscular adipocytes—more commonly known as marbling fat—are visible as the lines between sections of beef tissue, or the red meat.
Through biological and biochemical means, the researchers have isolated the adipocytes and grown them in culture systems. In those experiments, they discovered differences between subcutaneous adipocytes and intramuscular adipocytes. Marbling adipocytes are much smaller in size and diameter than subcutaneous adipocytes, which tend to clump together. Another difference is metabolic, or which energy source they use to produce back fat or marbling. Back fat adipocytes use acetate, which is a volatile fatty acid produced in the rumen of cattle. Marbling adipocytes, however, require glucose, which Johnson said is a premium energy source for both animals and humans.
The push from consumers to have more marbling and less fat, Johnson said, comes from the revelation that marbling appears to be very high in a healthy fatty acid called oleic acid. Oleic acid is a monounsaturated fatty acid that in humans has been shown to decrease low-density lipoprotein (LDL) cholesterol and possibly increase high-density lipoprotein (HDL) cholesterol.
The researchers concluded that U.S. beef producers can increase marbling and oleic acid synthesis in beef by feeding grain or corn. The most detrimental thing that can be done is grass feeding, or grazing, which reduces marbling.
