A Quantitative and Morphological Study of Bovine Longissimus Fat Cells

SUMMARY— A quantitative and morphological study was made of bovine fat cells from three marbling groups of longissimus muscle. Tracings on acetate paper were made of the visual marbling depots and the area measured at three positions with an ocular grid for both size and distribution of fat cells. Comparisons were also made of subcutaneous, intermuscular and intramuscular fat cell size. Intrafiber lipid accumulation was observed and the average number of red fibers per bundle determined. These results indicate that traceable intramuscular fat is not a good measure of total intramuscular fat. There did not appear to be a consistent medial, central and lateral marbling pattern among the three marbling groups; however, significant differences were apparent within groups. Fat cell size increased with increases in cell mass, marbling and total chemical fat of the muscle. Fat cells accumulated and grew in close proximity to portions of the circulatory system. Lipid deposits adjacent to the muscle contained larger fat cells than was evident in the extrafascicular spaces within the muscle. Intrafiber lipid was readily apparent in approximately 35% of the muscle fibers and probably represented either mitochondria or triglyceride. The interrelationship of subjective marbling scores, chemically determined fat, fat cell size, fat cell distribution and intrafiber lipid characteristics are complex and require complete investigation before the association of muscle fat and meat quality can be resolved.