UBC Theses and Dissertations
Some postmortem aspects of broiler breast muscle Wood, Darrell Fenwick
The ability of broiler P. major muscle to develop postmortem isometric tension was studied under a variety of conditions. Muscle strips developed and released tension while suspended in phosphate buffer pH 7.2.The addition of calcium or magnesium to the buffer enhanced tension release, as did the presence of either of these two ions and EDTA. Different rates of tension release v/ere evident from bird to bird and the rate of release was fastest in birds which required the shortest time to reach maximum tension. The proportion of tension released within one hour of reaching maximum tension correlated significantly with subsequent proportions from 2 through 12 hours after maximum tension, making it possible to predict, with reasonable accuracy, tension release from 1 hour values. The one hour release values had a significant relationship with time to maximum tension but no relationship with tenderness suggesting that tension release, from bird to bird, is not indicative of tenderness. Free struggle at slaughter, hot water scalding and mechanical plucking were shown to have an additive effect on tension parameters and tenderness of broiler P.major. Pre-slaughter epinephrine injection was shown to deplete muscle glycogen levels within 8-12 hours post-injection. ATP levels remained high resulting in considerable tension development. It appears that such tension development is sufficient to account for the subsequent toughening observed in the muscle. Broilers were subjected to three different stress situations (commercial handling, cold and heat). No significant changes in postmortem muscle quality were observed as a result of these treatments. Broilers appeared to respond differently under the different conditions with heat stress shortening the time to reach maximum tension and commercial and cold stresses lengthening the time to maximum tension. A cold shortening effect was observed during the study of the effect of temperature on tension pattern. The amount of cold shortening observed was increased as temperature was lowered from 5°C to 0°C. At 2°C, the initial cold shortening occurred and no further tension development was observed even after 36 hours at this temperature. Removal of strips from 2°C to room temperature after 12 and 24 hours resulted in some further tension development but essentially no tension was observed when 36 hour strips were brought to room temperature. The cold shortening did not significantly lower muscle ATP and creatine phosphate levels although a decrease was observed.
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