No abstract

The solubilities of sarcoplasmic and myofibrillar proteins were determined at the time of slaughter, onset of rigor mortis, completion of rigor mortis and 24 hr after death in muscles exhibiting a wide range of physiological conditions during the post-mortem period.Muscle protein solubility was grossly altered by the conditions of both temperature and pH which existed at the onset of rigor mortis or during the first few 'hours after death. Sarcoplasmic protein solubility at 24 hr was decreased to 55% of that found at 0 hr in muscle groups exhibiting high temperature and low pH at the onset of rigor mortis.Conversely, only a 17% reduction of sarcoplasmic protein solubility was noted in groups with high pH at onset. Myofibrillar protein solubility ranged from no reduction during the first 24 hr after death when pH remained high at onset to 75% reduction in muscle with low pH and high temperature at the onset of rigor mortis.The 24-hr pH of th e muscle appeared to have only a minor influence on protein solubility. Muscle protein solubility appeared to be one of the major factors affecting the juice-retaining properties of muscle.

SUMMARY Continuous recordings of pH and temperature changes, during postmortem chilling, were made on 20 Danish Landrace carcasses. The continuous recordings from these carcasses depicted at least four distinct types of post‐mortem pH patterns: 1) a slow gradual decrease to an ultimate pH of 5.7–6.3; 2) a gradual decrease to about 5.7 at 8 hr, with an ultimate pH of 5.3–5.7; 3) a relatively rapid decrease to about 5.5 at 3 hr, with an ultimate pH of 5.3–5.6; 4) a sharp, significant decrease to a pH of about 5.1 at 11/2 hr, and a subsequent elevation to 5.3–5.6. The first 3 types were acceptable in structure, color, and water retention, whereas type 4 represented pale, exudative tissue with soft, inferior structure. The violent nature of the post‐mortem changes in tissue with the type 4 pH pattern were discussed, as well as the possibility of a more rapid onset of rigor mortis in this tissue. Although the pH values of the pale, exudative tissue were elevated during chilling, it appeared that they remained generally lower, ultimately, than the normal tissue. On the basis of comparisons between muscles, it is suggested that in addition to chemical composition, the chilling rate of the individual muscle may also be an important factor in determining pH pattern and ultimate muscle structure.

Tenderness of semitendinosus and psoas major bovine muscles was markedly affected by: ( I ) allowing the muscle to undergo rigor mortis and the associated contraction, following pre-rigor excision, or by ( 2 ) pre-rigor excision followed by restraint in a stretched state while the muscle undergoes rigor mortis. The extent of stretch or contraction induced by pre-rigor treatment was reflected by the sarcomere length. The average sarcomere length of the semitendinosus and psoas major muscles differed widely when samples were removed post-rigor from the carcass. The data indicate that the state of contraction (measured by sarcomere length), when altered in different portions of the same muscle by treatment, or when varying naturally in different muscles, was associated with tenderness. IntroductionNumerous studies have been conducted during the past few years to determine the specific contribution of various factors to the tenderness of bovine muscle.l-12 One of the factors reported has been the difference in contraction state of myofibrils in bovine m~sc1es.l~ This worker postulated that the variations in sarcomere lengths among muscles, were due, in part, to the strains induced in the muscles when the carcass was vertically suspended, and also that since long sarcomeres occurred in muscles previously reported14 to be generally tender, the state of contraction was considered a factor contributing to tenderness, where the effect of connective tissue was small.Herring & Briskey5 noted that portions of bovine semitendinosus muscle, excised pre-rigor and stretched during cooking, were tender, while similar portions from the same muscle, excised and cooked in the free unrestrained state, shortened markedly and were tough.The present study was conducted in order to expand on the above general problem of tenderness and specifically to investigate further the report of Locker'3 which implicated muscular contraction in the problem of tenderness. Studies were made on different portions of the same muscle which were allowed to undergo rigor mortis under different experimental conditions in order to determine the relationships among contraction state, sarcomere length and tenderness.

SUMMARY The red fiber content of several porcine muscles was estimated by a histochemical method (affinity for Sudan Black B due to high intracellular lipid content) and a biochemical method (high succinic dehydrogenase activity). Even though the muscles varied widely in total lipid content, the histochemical method was comparable to the biochemical method in categorizing porcine muscles as red or white. Red muscles (> 40% red fibers) contained greater myoglobin concentrations and generally had longer post‐rigor sarcomeres than white (< 30% red fibers) muscles. Interrelationships of percent red fibers, succinic dehydrogenase activity, fat content, glycolytic rate, and post‐rigor contraction state were discussed.