Consumers in the U.S., Japan, and Korea have valued highly marbled beef for nearly a century. In the United States, most consumers prefer beef that is reasonably marbled and juicy. Early studies demonstrated that the more oleic acid in beef, the greater the overall palatability of the beef. Scientists have taken a two-prong approach to understand the biology of marbling development. Biochemists, molecular biologists, and geneticists have worked to gain a better understanding of the intracellular and extracellular factors that regulate the development of marbling adipose tissue (also known as intramuscular tissue), whereas beef cattle nutritionists have worked to optimize diets and time on feed to provide high-quality beef carcasses without exacerbating carcass adiposity. Marbling adipose tissue preferentially uses glucose as the carbon source for fat synthesis, whereas subcutaneous adipose tissue preferentially uses acetate. Early weaning of beef steers promotes greater marbling development at slaughter than normal weaning of steers, and this may be caused by increased glucose availability (from the grain-based rations) at the early stages of marbling development. In addition to providing carbon for marbling adipose tissue development, grain-based diets also increase monounsaturated fatty acids (MUFA) such as oleic acid in marbling by stimulating the expression of stearoyl coenzyme A desaturase (SCD). There is a significant correlation between the concentration of MUFA and amount of intramuscular lipid in longissimus muscle in cattle with the genetic propensity to marble that are fed grain-based diets for extended periods of time. Marbling adipose tissue can be distinguished from other fat depots by its location within perimysial connective tissues alongside muscle fibers. However, in longissimus muscle from Japanese Black A5 cattle, marbling adipocytes have been observed within muscle bundles, suggesting that muscle satellite cells can be induced to differentiate into marbling adipocytes. To date, the mechanisms responsible for this trans
-differentiation of satellite cells to adipocytes in beef cattle have not been identified, as this process is quite difficult to measure in in situ
. Marbling adipose tissue from Japanese Black cattle are exceptionally high in oleic acid, and recent cell culture studies have demonstrated that oleic acid promotes trans
-differentiation of muscle cells to marbling adipocytes. The results of these studies indicate that grain-based diets are necessary to promote the development of marbling. Furthermore, grain-based diets increase the healthfulness and juiciness of beef by promoting the production of oleic acid in marbling and other fat depots.
Keywords: Beef, marbling, oleic acid