Microstructure and thermal characteristics of Thai indigenous and broiler chicken muscles

The microstructure and thermal characteristics of Thai indigenous (Gallus domesticus) and broiler chicken (commercial line CP707) biceps femoris and pectoralis muscles were determined. Perimysium thicknesses were 14.2 micrometer for biceps femoris muscle and 7.10 micrometer for pectoralis muscle of indigenous chicken muscles, thicker than those of broiler muscles, which were 9.93 micrometer for biceps femoris muscle and 3.87 micrometer for pectoralis muscle (P < 0.05). Five endothermic peaks with peak transition temperatures (T(p)) of 54.9, 61.7, 65.4, 70.6, and 76.1 degrees C were obtained for broiler pectoralis muscle, whereas only 3 endothermic peaks (T(p) of 56.6, 62.6, and 74.9 degrees C) were obtained for broiler biceps femoris muscle. Thai indigenous biceps femoris and pectoralis muscles had endothermic peaks with T(p) ranges of 53.5 to 54.8, 60.7 to 61.9, and 75.9 to 76.9 degrees C. The fiber diameters of Thai indigenous chicken muscles were greater (P < 0.05) than those of the broiler, 31.7 vs. 20.4 micrometer for biceps femoris muscle and 28.9 vs. 26.6 micrometer for pectoralis muscle, respectively. After cooking at 80 degrees C for 10 min, the fiber diameter of indigenous chicken muscles significantly decreased while those of the broiler significantly increased. The mean of sarcomere lengths of the raw muscles ranged from 1.56 to 1.64 micrometer and decreased to 0.92 to 1.32 micrometer (P < 0.001) for broiler muscles and 1.22 to 1.35 micrometer (P < 0.001) for indigenous chicken muscles after cooking. The perimysium and endomysium of broiler muscles melted after cooking at 80 degrees C, however, only slight disintegration was observed in these tissues in the indigenous chicken muscles.