Thermal Gelation Profile Changes in Reconstituted Actomyosin due to Storage under a High Salt Concentration and Low Temperature

Changes in the heat-induced gelation properties of reconstituted rabbit skeletal actomyosin stored under a high salt concentration at pH 6.0 and 0°C were investigated at different weight ratios of actin to myosin by using dynamic rheological and biochemical measurements. The addition of actin resulted in a pronounced peak maximum at about 50°C and an accompanying temporary reduction in the range at about 50°C to 60°C. The more the initial actin concentration was increased, the greater was the area of the peak/shoulder. However, this area was markedly diminished with increasing storage time. As a result, the dynamic rheological pattern was transformed from an actomyosin type into a myosin type. The relationship between the G′ value at 80°C and the actin/myosin weight ratio was curvilinear, with a peak at the ratio of 0.05, immediately after storage was started. This profile changed during storage, depending on the extent to denaturation of actin and myosin in the reconstituted actomyosin (RAM). The G′ value of actomyosin in 0.5m KCl with a small actin/myosin ratio of 0.05 decreased to one-half of its initial value after 7 days of storage, whereas the G′ value with a large actin/myosin ratio of 0.225 increased by about 1.6 times. In 1.5 m KCl, all the G′ values declined to the level with myosin alone after 7 days of storage. The time–course plots of the remaining actin concentration in RAM at different weight ratios of actin to myosin after being treated with 0.5 m or 1.5 m KCl showed a decrease in the actin content with increasing storage time, and an increase in the KCl concentration to 1.5 m KCl promoted the denaturation of actin in RAM faster than with 0.5 m KCl. The surface hydrophobicity of each RAM sample progressively increased with increasing storage time, while little significant increase in the sulfhydryl (SH) content during storage was observed. It is concluded that changes in the heat-induced gelation properties of actomyosin during storage are largely attributable to the denaturation of actin rather than to the denaturation of myosin or to quantitative changes in the SH content and hydrophobicity.