Proteolysis and tenderisation in reindeer (Rangifer tarandus tarandus L.) bull longissimus thoracis muscle of varying ultimate pH.

Proteolysis and tenderisation in reindeer (Rangifer tarandus tarandus L.) M. Longissimus Thoracis were studied. Mm. Longissimus ( the part cut out between vertebrae thoracales 6-7 and vertebrae lumbales 5-6) from 12 reindeer bulls (age 1 1 2 years) were, after ultimate pH and temperature measurements, excised and then sampled at various times post mortem for determination of sarcomere length, Warner-Bratzler shear force, calpain and calpastatin activities, cathepsins B + L activities, active site titration of cystatin-like inhibitors, myofibrillar protein degradation, collagen content and heat solubility. Upon measurement of ultimate pH, the carcasses were divided into two pH groups; normal pH (5.65 ≤ pH ≤ 5.79) and high pH (pH ≥ 5.80). Temperature and pH fall were relatively rapid in all reindeer carcasses. Sarcomere lengths tended to be shorter in the carcasses of the high pH group. In the three carcasses with the highest ultimate pH values (6.11, 6.34 and 6.38), sarcomere lengths were around or below 40% of resting length (1.37μm, 1.25μm and 1.25μm, respectively) which is likely associated with the occurrence of heat shortening. Total collagen content was higher and heat solubility lower in the high pH group, which could have masked differences in tenderness. However, all reindeer longissimus muscle samples were found to be extremely tender regardless of ultimate pH. By 3 days post mortem Warner-Bratzler shear force values were varying between 2.1-4.9 kg cm(2). There was a significantly higher activity of μ-calpain in the high pH group at 1 day post mortem. No differences in shear force, myofibrillar protein degradation as observed by SDS-PAGE, m-calpain and calpastatin activities, calhepsins B+ L activities or the levels of cystatin-like inhibitors were found between the two pH groups.