Blackwell Publishing Journal Backfiles 1879-2005
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Process Engineering, Biotechnology, Nutrition Technology
SEM was used to determine the effect of postmortem aging (unheated) and cooking (heated to internal temperatures of 60, 70 and 80°C by broiling) on the ultrastructural characteristics of bovine longissimus and psoas major muscles. Micrographs from postmortem aged (unheated) muscle clearly showed the fibrillar and connective tissue structures of muscle. Progressive changes with increased temperature were observed in endomisial sheath swelling, collagen fiber disintegration and myo-fibril fragmentation, coagulation and shrinkage. Specifically, after heating to 70°C, banding patterns and myofibril fragmentation at Z-disks were clearly evident. Degradation of collagen fibers in the perimysium was initiated at 70°C and intense disintegration was observed at 80°C. Changes observed in psoas major were different from those in the longissimus in that intact myofibrils and tubules were observed in both the heated and unheated samples. This may be due to the “loose” packing of myofibrils unique to psoas major muscle. Furthermore, less shrinkage and coagulation of myofilaments in the A band region and wider I band regions were noted. These observations of looser packing of myoflbrils, thinner myotibril threads and wider I band regions offer additional evidence as to why steaks from psoas major muscle are more tender than those from longissimus muscle.
Type of Medium: