Author
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TAYLOR, RICHARD - INRA DE THEIX, FRANCE |
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Koohmaraie, Mohammad |
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Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/8/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Callipyge phenotype greatly improves feed efficiency, dressing percentage, and carcass composition. These advantages, combined with absence of dystocia (difficulty during birth), presents the lamb industry with an attractive method of efficiently producing lean meat. The major drawback to callipyge condition is its negative effect on meat tenderness. The negative effect of the callipyge condition on meat tenderness appears to be particularly large for the longissimus (meat from the middle part of the carcass, such as loin chops). Before the lamb industry can utilize the callipyge lamb, processes would have to be implemented to mitigate and possibly eliminate its negative effect on longissimus tenderness. The objective of the present experiment was to determine the biological mechanisms of toughness of callipyge meat. Transmission electron microscopy data indicated that meat from callipyge did not lose its structural integrity. The loss of structural integrity of muscle during postmortem storage of carcasses or cuts of meat at refrigerated temperatures is responsible for meat tenderization. Because these changes did not occur, meat from callipyge lamb does not undergo postmortem meat tenderization and, thus, it remains tough. The reason for lack of postmortem tenderization is the reduced activity of the enzyme system (the calpain proteolytic system) that is responsible for loss of structural integrity of muscle. Therefore, these results imply that processes which activate calpain should improve/enhance callipyge meat tenderness. Technical Abstract: These experiments were conducted to examine ultrastructural changes in longissimus from normal and callipyge lamb during a 14 d postmortem storage at 4 deg C. Six ewe and wether crossbred lambs (1/2 Dorset X 1/2 Romanov) were grain-fed and slaughtered at approximately 250 d of age. Leg conformation score was the basis for classifying carcasses into normal and callipyge. Longissimus was sampled after 1, 3, 7, and 14 d at 4 deg C. Transmission electron microscopy showed that the normal longissimus showed ultrastructural changes including sarcolemma detachment, intermediate filament loss, and I band breaks. Callipyge longissimus also had loss of sarcolemma attachments to myofibrils although delayed by several days in comparison to normal. However, callipyge did not show extensive loss of intermediate filaments, and had very few breaks in the I band region of myofibrils. The endomysium was intact postmortem in both normal and callipyge longissimus indicating that this structure does not contribute significantly to postmortem tenderization. We conclude that the major factor responsible for the toughness of meat from callipyge longissimus is the postmortem stability of myofibrils and myofibril associated cytoskeleton. |
