Salt- and pyrophosphate-induced structural changes in myofibrils from chicken red and white muscles

Myofibrils isolated from post-rigor chicken Pectoralis major (PM, white) and Gastrocnemius (Gas, red) muscles were irrigated with various concentrations of NaCl (0.1–1.0 M) with or without 10 mM sodium pyrophosphate at pH 5.5 and 6.0. Structural changes were examined using phase contrast microscopy. PM myofibril samples tended to show more definitive H-zones but obscure Z-lines compared to Gas myofibrils. Significant myofibril swelling, accompanied by a pronounced protein extraction, occurred in 0.5 M NaCl solution. The extent of swelling as well as protein extraction increased with the NaCl concentration up to about 0.8 M. Addition of pyrophosphate facilitated myofibril swelling and reduced the minimal NaCl concentration for swelling to 0.4 M. Without pyrophosphate, protein extraction for both PM and Gas myofibrils occurred along the A-band, sometimes starting from the centre, but when pyrophosphate was added, the extraction began from the ends of the A-band. At pH 5.5, protein extraction was similar for PM and Gas, but at pH 6.0, PM myofibrils were more extractable and their architecture changed more extensively than Gas myofibrils, especially when pyrophosphate was present. The results may explain the different water-imbibing abilities of white and red meat when processed with salt and phosphate.