India is a country where people have always preferred fresh food over preserved or canned food be it fruits, vegetables or even chappatis. With the majority of the Indian population being meat eaters, the same trend is followed in almost all the households i.e to get freshly slaughtered animal meat for cooking.
But did you know that a freshly slaughtered animal is not Meat but just a piece of Muscle!!
The conversion of muscles to meat involves a series of physical and chemical changes after an animal has been slaughtered. These changes require several hours or even days .The whole process of this conversion is known as Rigor Mortis.
So, What happens during Rigor Mortis
After the slaughter of the animal, bleeding results in no oxygen supply to the muscles and they become oxygen deficient. Homoeostasis is a process by which a living being maintains its internal body temperature with respect to the atmospheric temperature. When an animal is slaughtered, it loses its ability to maintain homeostasis.
Under normal aerobic conditions (in the presence of oxygen), energy in produced in the muscles in the form of ATP molecules ( adenosine triphosphate) along with the formation of carbon dioxide and water. The process is termed as glycolysis But in the case of anaerobic conditions (lack of oxygen) , fewer ATP molecules are produced. Lactic acid is also produced under anaerobic conditions by using the stored muscle glycogen.
The lactic acid decreases the pH of the muscle from 7.0 to around 5.3. The energy or ATP generation further decreases with the fall in the pH .
Lower pH also increases the permeability of the sarcoplasmic reticulum (part of the muscle cells that controls the level of calcium ions) . Its increased permeability causes the inflow of calcium ions into the muscle cells. The calcium ions bind to the muscle protein troponin and cause changes in the protein structure. This results in the release of ATPase enzyme.
The ATPase enzyme acts on the binding site of other muscle proteins , actin, and myosin and causes their cross-linking to form an actinomyosin complex. The formation of actinomyosin complex causes toughening and rigidity of the muscles. Thus the muscles become hard and lose their flexibility.
After Rigor Mortis
The whole process of rigor mortis starts after 9-12 hours of slaughter and stays up to 24 hours. After 20-24 hours, the low pH of the muscles denatures the muscle proteins. The protein denaturation and lower ATP level effectively contribute to increasing the pH. This leads to softening of the muscles and rigor mortis passes by. This is termed as the aging of the meat. Aging of the meat causes its tenderization and muscles gain back the extensibility. The rigor mortis is said to pass by at this stage.
Results of Rigor Mortis and aging
- The muscles become rigid and lose their flexibility due to the formation of protein cross linkages. The rigidity is lost when the aging stage is reached.
- The muscle becomes more susceptible to microbial attack since the defense mechanism of the body stops.
- The various protein structures get denatured which leads to the loss of structural integrity.
- Degradation is also favored by activation of certain enzymes at low ph. These enzymes such as cathepsins favor the degradation of connective tissues as well.
- The aging of the meat improves its flavor.
- The cooking time for an aged meat is less than the meat for which rigor mortis is ongoing as the meat has achieved tenderization.
- The nutritional loss is lesser while cooking an aged meat.
- The water holding capacity decreases during rigor mortis. This increases after aging of the meat which leads to juicy and better chewable meat.
In a nutshell
The process of conversion of muscle to meat i.e. rigor mortis starts after 8- 12 hours of slaughter. This time may vary according to the species of slaughtered animal, type of the muscle and various other factors. As every good thing takes time so does this conversion. Only after certain physio- chemical changes a muscle piece can be termed as meat. So next time before cooking or taking in a non-vegetarian dish, do think if it is actually meat or just a piece of muscle?