20. The Effect of Muscle Type and Time of Storage on Myofibrillar Protein Proportion in Beef

Tenderness is usually associated with the proteolysis occurring in muscles. However, most of the studies concentrate on one muscle only. The aim of this study was to describe the changes in myofibrillar protein percentage proportions during the ageing of 8 bovine muscles. Investigations were conducted on the muscles from different parts of the carcass, from the forequarter: m. pectoralis profundus, m. infraspinatus, m. triceps brachii, m. serratus ventralis, and from the hindquarter: m. biceps femoris, m. semimembranosus, m. semitendinosus and m. longissimus dorsi (thoracis et lumborum). The effect of muscle type was significant for all parameters except for percentage proportions of titin (3000÷3700 kDa), MHC (205 kDa) and protein fractions between <205÷42> kDa. Differences between the muscles varied depending on the analysed proteins and the time of storage. A significant effect of ageing time for titin, nebulin (approx. 800 kDa), proteins of molecular weight of 38 kDa, proteins smaller than 42 kDa and in the range of 3000÷205 kDa, 205÷42 kDa and 38÷20 kDa was observed. The decrease of percentage proportions of titin, nebulin and proteins in the range of 3000÷205 kDa and an increase of protein bands in the range of 38÷20 kDa and proteins below 42 kDa was also observed. During the storage period of beef from the 2nd to the 14th day, the progress of myofibrillar proteolysis was different in each muscle. The changes of tenderness were not related to shear force values. It is probable that the changes in other constituents of meat might influence the tenderness more than those in myofibrillar proteins.