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Sodium, potassium and magnesium chloride, at 1.25, 2.50 and S.OO%, were studied using differential scanning calorimetry. Increasing NaCl resulted in decrease in myosin transition temperature (T,, first transition) and enthalpy (I-I,); both showed significant (PcO.05) linear response. The sarcoplasmic proteins and collagen denaturation temperature (T,, second transition) increased significantly over the control when 1.25% NaCl was added, but were the same as control when 2.5% and 5.0% were used. Actin denaturation temperature (T3, third transition) tended to increase when NaCl was added, but enthalpy decreased. Potassium chloride showed similar effects to NaCl on T1, Tz. I-& and Ha. Increasing magnesium chloride had much more pronounced effect on decreasing second enthalpy compared to the monovalent salts. At 5% MgCI, T, increased significantly.

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Differential scanning calorimetry (DSC) of beef muscle produced three large endotherms occurring at 55–57°C, 65–67°C and 81–83°C. Based on earlier DSC research on isolated proteins (Privalov 1979), the concept of cooperative units participating in thermal transition phenomena was applied to beef muscle endotherms. Analysis of these endotherms by the van't Hoff relationship and Borchardt and Daniels kinetics analysis revealed reaction orders of ca. 0.6 to 2.1, 3.5 to 5.1 and 1.5 to 3.1, respectively, for the three muscle endotherms. The reaction orders for these endotherms were influenced by muscle type, fiber sarcomere length and conditioning. Aging led to an increase in reaction order whereas increased sarcomere length was accompanied by a decrease in reaction order or number of cooperative units. Changes in the number of cooperative units participating in the endotherms is discussed in the context of meat tenderization and conditioning. It appears reaction order analysis of the T3 transition (81–83°C) may correlate with meat tenderness.