2.1. Animals and muscle samples
The slaughter plant used electrical stunning, and the pigs were exsanguinated and then placed in a dehairer at 65 °C for 5 min. Any remaining hair was removed with a flame and knife after exiting the dehairer. After evisceration, the carcasses were weighed and the carcass percentage calculated. The loin eye area was also measured at the level of the last rib. Back-fat thickness was measured at the 11th and last thoracic vertebra, and the mean of these two measurements was used as the back-fat thickness value.
At 45 min postmortem, muscle samples were taken from the longissimus dorsi muscles at the 7 and 8th thoracic vertebra of the carcass for the analysis of muscle pH (pH45 min) and lightness (L⁎). At the same time, muscle samples were cut into 0.5×0.5×1.0 cm3 pieces, then immediately frozen in isopentane using liquid nitrogen, and stored at −80 °C for the subsequent analysis, including muscle fiber characteristics and R-value. After 24 h in a 4 °C cold room, the pork loins (the 9–13th thoracic vertebra) were taken for meat quality measurement, then immediately frozen and stored at −80 °C for protein solubility measurement.