On the water-holding of myofibrils: Effect of sarcoplasmic protein denaturation

• A new hypothesis: heat-denatured sarcoplasmic proteins improve water-holding.
• The influence is compartmentalized.
• Denatured sarcoplasmic proteins shrink the myofilament lattice spacing.
• Denatured sarcoplasmic proteins may form a network outside of myofibrils.
• The network traps water and counteracts water loss from denaturation of myofibrils.

The role of heat-denatured sarcoplasmic proteins in water-holding is not well understood. Here we propose a new hypothesis that in PSE-like conditions denatured sarcoplasmic proteins aggregate within and outside myofilaments, improving the water-holding of denatured myofibrils. The process is compartmentalized: 1) within the filaments the denatured sarcoplasmic proteins shrink the lattice space and water is expelled; and 2) between the myofibrils and in the extracellular space, the coagulated sarcoplasmic proteins trap the expelled water from interfilamental space. The effect of sarcoplasmic proteins on the water-holding of myofibrils following incubation for 1 h at 21 to 44 °C was investigated. Our results were consistent with the new hypothesis. Myofibrils without sarcoplasm had the poorest water-holding. With increasing amount of denatured sarcoplasmic proteins, the water-holding of heat-denatured myofibrils improved proportionally. X-ray diffraction was used to measure the lattice space between the filaments. Precipitated sarcoplasmic proteins shrank (P < 0.001) the lattice spacing by 6.3% at 44 °C.