Modelling the effect of sarcomere length on collagen thermal shortening incooked meat: consequence on meat toughness

Normal and contracted pieces of Semimembranosus and Longissimus Dorsi muscl es from cull cows were cooked for 90 min at temperatures up to 80 degrees C . For both muscles, at 50 degrees C the normal samples have higher breaking stress than contracted samples. The breaking stress of normal samples decr eases at 55 degrees C. This decrease is not observed for contracted samples . The contracted samples become the tougher above 60 degrees C. Drip and co oking losses are the highest in contracted samples. Sarcomere length decrea ses above 60 degrees C whatever the raw sarcomere length. The amplitude of thermal shortening of perimysium collagen fibres in cooked meat has been ca lculated. This theoretical model takes into account the changes in the wavi ness of collagen fibres associated with changes in raw sarcomere length and the geometrical changes of fibre bundles due to drip, cooking losses and c ooking shortening. The calculations lead to the conclusion that thermal sho rtening of collagen fibres at 60 degrees C is lower in contracted samples t han in normal samples. As the final modulus of collagen fibres decreases wh en their thermal shortening increases, this can explain part of the differe nces observed between the toughness of normal and contracted cooked meats. In particular, it can explain why contracted cooked meat becomes tougher th an normal meat just above 60 degrees C and why there is a decrease in norma l meat toughness between 55 and 60 degrees C. This work therefore emphasise s the role of collagen in toughening associated with cold shortening. (C) 1 999 Elsevier Science Ltd. All rights reserved.