Calpain-calpastatin and toughness in M-longissimus from electrically stimulated lamb and beef carcasses

Shear strength, pH, temperature, mu-calpain, m-calpain and calpastatin leve ls were measured over a two-week post-slaughter period in Longissimus lumbo rum et thoracis (LD) from six lamb and six beef carcasses. All carcasses we re subjected to high voltage electrical stimulation. The toughness of the b eef LD determined by a MIRINZ tenderometer at 24 h post-slaughter showed a strong correlation (r = 0.91) with pH of the LD at 3 h. Beef LD toughness a t 14 days was correlated (r = 0.84) with initial m-calpain levels. In both lamb and beef, LD toughness at 4 and 14 days respectively was also correlat ed with initial levels of calpastatin (r = 0.85, 0.83, respectively). The s trong correlation between calpastatin and the rate of tenderisation indicat es that the calpain system is closely linked to the proteolytic breakdown o f myofibrillar proteins. There is also evidence of an interaction between p H and mu-calpain activity. The mu-calpain, m-calpain, calpastatin, pH and t emperature kinetic changes which occurred during the post-mortem ageing of beef and lamb LD were applied to a computer program which predicted rate of meat tenderisation by calculating in situ calpain activity. The closeness of fit between the predicted rate of meat tenderisation and the observed te nderness values of beef and lamb LD indicates that the post-mortem activity of mu-calpain is the major determinant of variations in tenderness. Howeve r, application of the meat tenderisation predictive program to LD from indi vidual animals revealed that the program was not sufficiently robust for th is use. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.