Myofibrillar shortening and ultrastructural changes in prerigor heated beef triceps brachii muscle

Teofilo Jose Pimentel da Silva, Purdue University

Abstract

Heating rate effects on degree of myofibrillar shortening and ultrastructural changes in prerigor beef triceps brachii muscle were studied. Three experiments were performed: (1) Muscle samples from six cattle heated at rates of 2$\sp\circ$C/2 min and 2$\sp\circ$C/12 min beginning at 31$\sp\circ$C and ending at 53$\sp\circ$C and 47$\sp\circ$C (control held at 37$\sp\circ$C) were used to evaluate electron microscopy sample preparations; (2) Samples from six additional cattle were prepared as in experiment 1, and used to evaluate myofibrillar shortening, ultrastructure changes of myofibrils and correlative microscopy; (3) Samples from three other cattle were prepared as in experiment 1, and used to observe the fracture behavior of muscle cells and connective tissue. Micrographs from scanning electron microscopy cold stage/high ice sublimation or cryoprotectant, regular stage/fixative/freeze-fracture, and transmission electron microscopy were appropriate for exposing detail of inter- and intracellular structures, for quantitative measurements and for minimal artifact formation. Rapid heating (2$\sp\circ$C/2 min) caused more severe myofibrillar shortening and shorter sarcomere length as compared to slow heating (2$\sp\circ$C/12 min). Micrographs showed that rapid heating resulted in extensive loss of organized myofibrillar structure, whereas slow heating caused extensive shortening, but not extensive disruption of myofibrils. Sarcomere length and spacing between intermyofibrillar connections were similar among electron microscopy preparations. Results indicate that the transverse structures viewed by conventional SEM and the intermyofibrillar connections viewed by cryogenic SEM are probably Z-disks. Rapid heating caused maximum separation of fiber bundles from each other. This separation and fracture occurred somewhere near the perimysial/endomysial junction. Also, showed a granular endomysium and large number of supercontraction nodes alternating with areas of sarcolemma fragmentation and fiber tearing in muscle heated rapidly. These experiments identified ultrastructural components of muscle that are disrupted by heat-induced active muscle contraction. Alternations of myofibrillar structure, separations of muscle cells and fracture of connective tissue account for enhanced tenderness of rapidly heated prerigor muscle. Minimal changes in ultrastructure of slowly heated muscle explain its lack of tenderness.

Degree

Ph.D.

Advisors

Judge, Purdue University.

Subject Area

Food science

COinS