CONTRIBUTION OF RIGOR SHORTENING AND COLD SHORTENING TO VARIABILITY IN THE TEXTURE OF PECTORALIS MAJOR MUSCLE FROM - COMMERCIALLY-PROCESSEDBROILERS

1. Three experiments were conducted to establish the degree to which c old shortening and rigor shortening contribute to variability in the t exture of Pectoralis major (PM) muscles of commercially processed broi ler carcases chilled at different rates. 2. In the first experiment, f ree range and standard broiler carcases were air-chilled under normal commercial conditions at 0 degrees C. Strong negative correlations bet ween pH values 15 min post-mortem (pH(15) (min)) and sarcomere length indicated that some cold shortening had occurred, while evidence suppo rting the occurrence of rip or shortening was much weaker. Regardless, of the cause of muscle shortening, weak negative correlations between shear force and sarcomere length indicated that shorter sarcomeres we re associated with tougher meat. In addition, strong negative correlat ions between pH values 24h post-mortem (pH(24h)) and cooking losses su ggested that increased juiciness is associated with higher ultimate pH values. 3. In the second experiment, carcases were either chilled rap idly in water at 0 degrees C (23 h) or in water at 10 degrees C (10 h or 23 h) to identify the individual contributions of cold and rigor sh ortening to textural variability more precisely. In carcases chilled r apidly in water at 0 degrees C, textural variability was low and tough ness was absent, suggesting an absence of both cold and rigor shorteni ng. However, few of these carcases had PH15 min values sufficently hig h (greater than or equal to 6.70) to promote a cold shortening effect. In contrast, carcases chilled in water at 10 degrees C, which had a s imilar deep muscle cooling rate as air-chilling at 0 degrees C, showed evidence of rigor shortening, because they had a wider range of sarco mere lengths and higher shear force values than carcases chilled in wa ter at 0 degrees C. 4. In the final experiment, carcases were either c hilled in air at - 12 degrees C, a cooling rate similar to that ofwate r-chilling at 0 degrees C, or chilled in air at 0 degrees C. Cold shor tening and increased toughness was evident with both chilling regimens in those carcases with pH(15) (min) values greater than or equal to 6 .70. In contrast, in carcases with PH15 (min) values <670, both chilli ng regimens reduced sarcomere shortening and improved tenderness. Howe ver, the mean shear value of the carcases chilled in air at - 12 degre es C was almost 1.00 kg cm(-2) lower than those chilled in air at 0 de grees C. 5. In conclusion, both cold shortening and rigor shortening c an occur during the commercial air-chilling of broilers at 0 degrees C and thereby contribute considerably to textural variability and incid ences of toughness. Faster chilling, either in water at 0 degrees C or in air at - 12 degrees C, has been shown to eliminate the risk of adv erse rigor shortening and toughness.