Post mortem changes in the mechanical properties and ultrastructure of the Longissimus in two porcine breeds

Kinetics of postmortem muscle changes of two pig breeds were studied. pH was measured at 30 min (pH1) and 26 h (pH2) after slaughter. The longissimus thoracis et lumborum was used at 1, 2, 3, 6 and 14 days postmortem for measurements of sarcomere length and mechanical properties in the raw state, and cooking loss and mechanical properties after cooking. Electron microscopy was performed at 1, 6 and 14 days postmortem. pH1 was higher and the maximum stress lower in Large Whites than in Pietrains. Maximum stress of cooked meat decreased with aging time in Large Whites but not in Pietrains. Ultrastructural changes were more obvious in Large Whites than in Pietrains through day 6, but breed differences were no longer observed at day 14. Meat from Pietrain pigs was tougher than that from Large White pigs and tenderized at a slower rate and to a lesser extent during aging.