Scanning Electron Microscopy of Bovine Muscle: Effect of Heating on Ultrastructure

Abstract

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 myofibril fragmentation, coagulation and shrinkage. Specifically, after heating to 7O"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.

Postmortem Delay Time and Heating Rate Affect Tenderness and Ultrastructure of Prerigor Cooked Bovine Muscle

“…This indicated that the area of Z disks might be the weakest point along the myofibrils for postrigor samples. This confirmed results of many other researchers (Cheng and Parrish, 1976;Jones et al, 1977;Heame et al, 1978;Davey and Dickson, 1970;Leander et al, 1980). The sarcomere length from this micrograph was 1.72~.…”

Effect of cooking method on mechanical properties, color and structure of beef muscle (M. pectoralis)

“…The samples were cut perpendicular to the direction of muscle fibers. On the transverse sections of raw muscles, Table 4 Coordinates L * a * b * for beef steaks cooked at 70°C at 15, 30, 45 and 60 min the gaps between the fibers and endomysial tubes were very clear, and had typical dendrite structure produced by a cryoconcentration of proteins and water losses (Palka, 1999;Palka & Daun, 1999).Whereas in samples cooked at 70°C, remarkable structural changes appear due to protein denature, such as water loss, destruction of cell membranes (Rowe, 1989), transversal and longitudinal shrinkage of meat fibers, the aggregation and gel formation of sarcoplasmic proteins and the shrinkage and solubilitation of the connective tissue (Bendall & Restall, 1983;Cheng & Parrish, 1976). The micrographs (Fig.…”

“…The greatest differences can be observed between raw meat and the cooked ones. Firstly it can be observed in the samples treated to 70°C, remarkable structural changes appear due to: the reduction of the water content, cellular membrane destruction, cross-sectional and longitudinal shrinkage of muscular fibers, aggregation and gel formation of sarcoplasmatic proteins and the shortening and solubilization of the connective tissue that cause the appearance of a granular aspect of the fibers (Bendall & Restall, 1983;Cheng & Parrish, 1976;Palka, 1999;Palka & Daun, 1999;Rowe, 1989).…”

“…The components of muscle that control toughness are the myofibrillar proteins and the connective tissue proteins, collagen and elastin. The structural changes that cooking brings about in the different proteins in their structural environment of the meat have been investigated by many authors (Bendall & Restall (1983); Cheng & Parrish (1976) ;Jones, Carroll, & Cavanaugh (1977)). During heating, the different meat proteins denature and they cause structural changes in the meat, such as the destruction of cell membranes, shrinkage of meat fibers, the aggregation and gel formation of myofibrilar and sarcoplasmic proteins and shrinkage and solubilisation of the connective tissue (Tornberg, 2005).…”

The effects of enzyme and phosphate injections on the quality of beef semitendinosus

“…These hydrolytic effects could not have been expected for the elastic connective tissue component, however, since elastin does not undergo thermal transition below 100°C (Rowe 1986). Cheng and Parrish (1976) demonstrated degradation of perimysial fibres beginning at 70°C and increasing in intensity at 80°C. Furthermore, Davey and Gilbert (1974) speculated on the development of myofibrillar fragility near 80°C.…”