Myosin solutions and suspensions have been monitored during heating at pH 6.0 by using dynamic rheological measurements. The storage modulus (G'), the loss modulus ( G ) and the phase angle (6) all showed a marked dependence on ionic strength in the temperature range 25-75°C. The filamentous gels (ionic strength <0.34) displayed a temporary reduction in G' at temperatures between 50 and 60°C, presumably due to denaturation in parts of the rod portion of the myosin molecule. In the same temperature region the concentration dependence of G' changed by a power of 2. The loss modulus also showed a marked concentration dependence, while the phase angle varied with concentration primarily at low (-40°C) temperatures. For the final gels, heated to 75"C, only G' indicated marked differences due to different protein concentrations and ionic strengths; all gels were almost completely elastic (&lo).Adenosine triphosphate was shown to have a pronounced temporary effect on the filamentous gel formed at low temperatures, i.e. on the gel with the highest concentration dependence, while pyrophosphate had no such effect. However, both adenosine triphosphate (or rather its hydrolysis product: adenosine diphosphate) and pyrophosphate appeared to have a small, lasting effect on the heat-gelling ability of myosin: the former a detrimental effect, the latter an improvement.

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Myofibrillar tissue from pale, soft, and exudative (PSE) pork was compared to tissue from normal pork by differential scanning calorimetry at pH 5.4. Thermograms of myofibrillar tissue from normal pork were characterised by three major peaks with temperature maxima at 58 and 66"C, associated with myosin denaturation, and at 78"C, associated with actin denaturation. In thermograms of PSE pork, the peak at 58°C was markedly reduced, and appeared as a shoulder. When the thermograms were divided into segments corresponding to the three major peaks, the area of the low temperature myosin segment was shown to be reduced by about 50% in PSE pork, as compared to normal pork. This indicates approximately 50% denaturation of the least thermostable parts of the myosin molecule. The more thermostable parts of the myosin molecule were largely unaffected, as was actin.

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Formation of bovine myosin gels (10 mg ml-I) by heat treatment at pH 6 and an ionic strength of 0.24 M has been monitored by using the Bohlin Rheometer System in the oscillatory mode. Rheological thermograms were determined with a general repeatability of about 2% for a given suspension. A pronounced maximum and an accompanying minimum in storage modulus (G') were found at about 50 and 55"C, respectively. The thermograms for the loss modulus (G") and the phase angle (6) displayed complex behaviour as well, suggesting a multitransition process. Presumably, denaturational events in parts of the molecule are responsible for the complex rheology observed. This complexity is not related to trivial wall slippage as data obtained from cells with different gap sizes were highly reproducible and consistent with other measurements. A decrease in heating rate from 2.5 to 0.1"C min-' had a large effect on G'; it increased from 905 to 1600 N m-* for gels at 75°C. The phase angle was also affected by the heating rate, especially at about 55°C. The effect of increasing the strain from 0.003 to about 0.1 was significant in two temperature regions; G' at temperatures higher than 65°C and 6 at temperatures lower than 54°C increased with increasing strain.