Relationship between weakening of Z-disks and liberation of phospholipids during postmortem aging of pork and beef

The liberation of phospholipids from Z-disks was investigated to elucidate the cause of the structural weakening of Z-disks, which contributes to the tenderization of meat during postmortem aging. The amounts of lipids in Z-disks were 2.2 g per 100 g of myofibrillar proteins in porcine and 2.7 g in bovine semitendinosus muscles. Phospholipids were the major component of the lipids. The postmortem liberation of phospholipids correlated well with Z-disk weakening, though alpha-actinin, the major protein of Z-disks, remained unchanged even after prolonged aging of pork and beef. We therefore concluded that Z-disks are weakened by liberation of phospholipids during postmortem aging of pork and beef.