Tensile properties of ovine skeletal muscle fibres: Thermal denaturation and selective removal of titin.
Marsh, J. M. (2005). Tensile properties of ovine skeletal muscle fibres: Thermal denaturation and selective removal of titin. (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/13251
Permanent Research Commons link: https://hdl.handle.net/10289/13251
The stiffness of chemically skinned single ovine skeletal psoas major muscle fibres is affected by many post-mortem events. These same events produce highly variable eating quality attributes in whole meat. This thesis focuses on three aspects of these events; sarcomere length, titin degradation and heat. Each of these factors was experimentally manipulated in vitro and the effect on the stiffness of single muscle fibres was measured. A technique was developed to apply strain to the fibre while recording the corresponding stress output. To study the effect of sarcomere length on single fibre stiffness before and after heating to 80°C (cooking), each fibre was set to one of six sarcomere lengths; 1.6, 1.8, 2.1, 2.7, 3.0, and 4.2 μm. Oscillations of 5 Hz were designed to stretch each fibre by 5 nm/half sarcomere. At sarcomere lengths below resting length (2.1 μm), the stiffness of uncooked fibres remained relatively unchanged, but appeared to increase in cooked fibres in proportion to the sarcomere length prior to cooking. The effect of selective titin degradation on the structural characteristics of single fibres, before and after cooking, was also examined using a low concentration of trypsin to selectively digest titin. The stiffness of raw fibres was unaffected by titin removal, but heating to 80°C caused significant changes in the stiffness of trypsintreated fibres. Two fixed sarcomere lengths were subsequently used to demonstrate the temperature dependence of fibre stiffness; l.6μm and 2.lμm. Although the fibre stiffness response at both sarcomere lengths was similar during heating, when the temperature was reduced from 80°C the response of fibres with a sarcomere length of 2.1 μm exhibited lower stiffness responses to each temperature than fibres with a sarcomere length of 1.6 μm. The length of the I-band appears to be important, especially after cooking. As shown in Chapter 2, the length of the I-band contributed to the final stiffness of the thermally denatured fibres, independent of the number of cross-bridges that had formed prior to cooking. As the I-band increased in length in the raw state, the more compliant the fibres became after cooking. This thesis provides information on, and a better understanding of, the structural and mechanical properties of single muscle fibres as a result of three different postmortem factors. Understanding how these factors affect the meat on a cellular level can help us to better control the environmental and postmortem influences on whole meat quality.
The University of Waikato
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