The structural basis of cooking loss in beef: Variations with temperature and ageing.

Meat loses fluid during cooking, resulting in textural changes and loss in cook yield. To understand the structural basis of cooking losses, this work used 10 bovine semitendinosus muscles and two ageing periods (1 vs 14days) to examine micro- and macro-level dimensional changes in muscle during heating. Muscle blocks, muscle fibre fragments and myofibrils all showed similar maximum shrinkage in cross sectional area (20-24%) but maximum length shrinkage was less in myofibrils (15%) than muscle blocks and fibre fragments (25%). Dimensional changes were dominated by shrinkage in individual muscle fibres and myofibrils, indicating that connective tissue does not play a major role. Transverse shrinkage predominantly occurred over 50-65°C whereas the longitudinal shrinkage predominantly occurred over 70-75°C; we attribute these two separate shrinkage events to denaturation of myosin and actin respectively. Higher cook losses in samples aged for 14days versus 1day suggests that desmin, nebulin and titin denaturation are not major drivers of fluid expulsion as these proteins are degraded during ageing. We postulate that proteolysis during ageing produces protein fragments which are more easily lost from the structure during cooking, along with water.