Transversal variation of intramuscular fat and morphological characteristics of bovine longissimus thoracis et lumborum muscle.

This study investigated the transverse variation in intramuscular fat (IMF) distribution within the bovine longissimus thoracis et lumborum (LTL) muscle, focusing on morphological and structural differences. The LTL muscles (n = 30) were sampled from the left side of the beef carcass between the 13th thoracic and 1st lumbar vertebrae (approximately 10 cm thick), targeting the central point of the bipennate structure. The medial (featherbone side) and lateral (rib side) regions, divided by the aponeurosis, were compared for muscle fiber and IMF particle characteristics. The area of loin-eye was significantly larger in the lateral region, whereas the pennation angle and IMF particle size were larger in the medial region (P < 0.05). IMF particle density or fatty acid composition were not significantly different (P > 0.05) However, type IIA and IIX fiber ratio, certain amino acids, pH, and shear force showed significant regional differences (P < 0.05). These results highlight morphological variation, particularly in fiber orientation and pennation angle differences at each region, which are accompanied by differences in IMF particle distribution. Understanding these intramuscular differences can improve the accuracy of beef quality assessments and provide insight into quality variation within a single cut or steak, thereby supporting both industrial practices and consumer awareness.