Model 506

For D0 and D5 samples, after storage (24 h at 4°C), 1 g of Pectoralis major muscle was crushed with an Ultra-Turrax T25 (Janke and Kunkelika-labortechnick) in 9 ml of a solution of KCl-iodoacetate (sodium iodoacetate 5 mM, KCl 150 mM). The pH of this solution was then measured using a portable pH meter (model 506; Crison Instruments SA, Alella, Bercelona, Spain) with a glass electrode.
At day 42, pHu was recorded in the right Pectoralis major muscles sampled on chickens originating from 213 birds from the pHu+ line and 212 birds from the pHu− line. At this age, the pHu was measured 24 h post-mortem using a portable pH meter (model 506, Crison Instruments SA, Alella, Barcelona, Spain) by direct insertion of its glass electrode into the muscles.

The present study was carried out on chickens belonging to the sixth generation of two lines divergently selected for high (pHu+) or low (pHu−) pectoralis major muscle pHu values^{12 (link)}. The birds were reared and slaughtered at 6 weeks of age at the PEAT experimental unit (INRA, Centre Val de Loire, Nouzilly, France). The broilers received ad libitum food and water until 8 h before slaughtering. Fifteen minutes after slaughter, samples of pectoralis major were collected, immediately snap frozen in liquid nitrogen and stored at −80 °C until RNA extraction. The pHu of the pectoralis major muscle was measured a day after slaughtering using a pH meter by direct insertion of the glass electrode (model 506; Crison Instruments SA, Alella, Bercelona, Spain) into the thickest part of the muscle. The pectoralis major quality was also assessed by the measure of glycolytic potential, lightness, drip loss during storage, toughness after cooking and processing yield as already fully described in Alnahhas et al.^{12 (link), 13 (link)}. A sub-sample of 16 pHu− and 16 pHu+ male broilers was selected for further analysis from the entire population, exhibiting extremely low (≤5.6) and high (≥6.2) breast muscle pHu values, respectively.