Sensitivity to ionic strength of MgCa-enhanced ATPase activity as an index of myofibrillar ageing in beef

Modifications of MgCa-enhanced ATPase activity and its sensitivity to ionic strength were studied during the conditioning of beef Longissimus dorsi muscle, together with the changes in the mechanical properties of the myofibrillar structure assessed instrumentally by a compressive test. As the storage time increases, the ATPase activity increases at low ionic strengths whereas it decreases at higher ones. Concomitantly, we observe an increment, with storage time, in the slope of the straight line graph obtained when plotting this ATPase activity against KCl concentrations. This slope enhancement is parallel with the decrease in the maximum compressive strength. Furthermore, these two changes have been significantly correlated (P < 0·01). We conclude that the slope value which quantifies the sensitivity of the ATPase activity to ionic strength could be an accurate indicator of the degree of ageing of the myofibrillar structure and has been called the Biochemical Index of Myofibrillar Ageing (BIMA).