Shortening of the Pectoralis Muscle and Meat Tenderness of Broiler Chickens

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The pectoralis muscles of broilers were either excised immediately after picking (hot-boned) or after 24 h of aging on the carcass. Gross muscle shortening along selected lengths, muscle area loss, and sarcomere shortening were calculated for the raw and cooked muscles of both treatments. Cooked meat tenderness was also evaluated at selected intramuscular locations. For hot-boned muscles, shortening after excision was about 10% along a shorter length confined and parallel to the region of clavicular origin, compared with 2% along a longer length parallel to the tendinous partition between the medial belly and lateral portion, and 16% when expressed as muscle area loss. After 24-h chill, hot-boned muscles had shortened 21% along the shorter length, 8% along the longer length, and 20% as area loss. After cooking, in the same comparison, the shortenings averaged 32% and 24%, and area loss 42%, respectively. The linear shortenings of the hot-boned muscles were related to area loss in an empirical model. Shear and texture values of the cooked meat indicated a difference due to location, which seemed consistent with the model of complex muscle shortening for this group. For muscles aged on the carcass, postchill (postexcision) and postcook shortenings, respectively, averaged 9 and 22% along the shorter length, 1 and 20% along the longer length, and 10 and 36% as area loss. Postcook decreases in sarcomere length averaged 6% for hot-boned muscles and 32% for those aged on the carcass.