Meat Science

RIGOR MORTIS

• It refers to stiffening of muscles after death and is another important postmortem change in the process of conversion of muscle to meat. It is now very well-known that a particular level or concentration of ATP complexed with Mg⁺⁺ is required for breaking the actomyosin bond and bringing the muscle to a relaxed state and as it drops, permanent actomyosin crossbridges begin to form and muscle gradually becomes less and less extensible under an externally applied force.
• During the period immediately following exsanguination, the actomyosin formation proceeds very slowly at first and the muscle is relatively extensible and elastic. This period is called the delay phase of rigor mortis.
• Then actomyosin formation picks up and the muscle begins to loose extensibility. This phase is called the fast or onset phase of rigor mortis. When all the creatine phosphate (CP) is depleted, ADP can no longer be phosphorylated to ATP, muscle becomes quite inextensible and stiff.
• This stage marks the completion of rigor mortis is rapid. When postmortem pH decline is very slow or very fast, the onset and completion of rigor mortis is rapid. The onset of rigor mortis is enhanced at ambient temperature above 20°C.
• The phenomenon of rigor mortis resembles that of muscle contraction in a living animal muscle except that rigor mortis is irreversible under normal conditions.

• The resolution of rigor mortis takes place mainly due to proteolytic activity of lysosomal enzymes or microbial degradation of muscle structure in due course of time.
• Pre-rigor meat is quite tender but its toughness keeps on increasing until rigor mortis is completed.
• It continues to be tough for some more time. However, with the resolution of rigor due to denaturation or degradation or aging, meat becomes tender.
•  The onset of rigor mortis is also accompanied by a decrease in water holding capacity. This is true even when rigor mortis takes place at a high pH due to disappearance of ATP and consequent formation of actomyosin.