Pressure treatment of meat: Effects on thermal transitions and shear values

The effects of pressure treatment (150 MN m(-2) for 3 h at 0°C) on the pH, thermal transitions, ultrastructure and Warner-Bratzler shear values of post-rigor beef semimembranosus and longissimus dorsi muscles have been investigated. Pressure treatment resulted in a slight but significant increase in pH. Differential scanning calorimetry revealed large changes in the thermograms of muscle samples as a result of pressure treatment, in particular a transition attributed to F-actin was absent in the pressure-treated sample. Examination of the ultrastructure also revealed extensive change as a result of pressure treatment, particularly in the I-band and M-line region. Pressure treatment either did not change shear values or increased them, according to whether the muscle was in the stretched or contracted state, respectively. The results are thought to support a theory for contraction state toughness proposed by Voyle (1969) in which increasing toughness is caused by an increasing incidence of sarcomeres in which thick filaments have been compressed onto the Z-line, thus removing the I-band as a zone of weakness.