U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


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Published in Beef Research Program Progress Report (1993) No. 4 (Part 1): 137-138


Variation in meat tenderness that exists among animals may be due to genetics, diet, age, and other factors. Results from the Germplasm Evaluation (GPE) program show that rib eye steaks from many of the Bos indicus breeds of cattle are less tender than steaks from most of the European (Bos taurus) breeds of cattle, although Bas indicus crossbreeding programs are advantageous due to hybrid vigor and insect and heat resistance in subtropical regions. Because consumers consider tenderness to be the principal component of cooked beef quality, it is important to determine the biological factors that regulate meat tenderness. If this knowledge can be obtained, steps could be taken to decrease the variation in meat tenderness; thus, red meat producers could consistently provide consumers with a tender product.

Factors affecting meat tenderness have been studied by U.S. Meat Animal Research Center scientists for many years. Some factors that may affect tenderness include muscle pH (acidity), rate of temperature decline after slaughter, muscle cell length (an indicator of the state of muscle contraction), the amount of total and soluble collagen (a form of connective tissue), muscle type (red vs white muscle types), and muscle enzyme activity. Of the many enzymes found in muscle, the calpain proteolytic (enzyme) system is thought to have a major role in the meat tenderization process. These calpain enzymes occur naturally in muscle tissue as well as a specific protein, known as calpastatin, that inhibits the activity of these enzymes. Two forms of calpain exist, µ-calpain which requires low calcium concentrations for activity, and µ-calpain which requires high calcium concentrations for activity. Therefore, µ-calpain is the form that is active in muscle tissue after slaughter. During the aging or storage of meat, this enzyme system is active in degrading certain muscle proteins which must occur for meat to be tender. If the activity of this system is hindered in any way or potential for activity is lost, then tenderness is ultimately affected. Therefore, much emphasis has been placed on understanding this enzyme system.

This report summarizes results from experiments which were designed to determine which mechanisms associated with tenderness can best explain the differences or variation observed in tenderness between Bos indicus and Bos taurus breeds.