How slaughtering conditions affects the meat tenderness

Both the conditions preceding slaughter and the handling of the carcass immediately afterward affect the tenderness of the meat. If the animal is under stress from fear, fasting, temperature extremes, or exercising, its muscle cells may be deprived of oxygen. When this occurs, the cells switch to anaerobic energy sources such as glycogen, which is converted to lactic acid, causing the pH to fall. A poor-quality meat will result if the glycogen has already been converted to lactic acid prior to slaughter.

Within 6 to 24 hours after slaughter, the muscle of livestock enter the state of rigor mortis, which is Latin for “stiffness of death”. This condition reverses naturally one or two days after slaughter. Rigor mortis is caused by a cascade of events that take place at the cellular level. Death interrupts the blood flow and prevents oxygen from reaching the cells. Changes than occur within the cells of the muscles, causing them to contract and stiffen. The rigidity of the muscles in rigor mortis occurs because the cross-links between the actin and myosin filaments overlap and cause the sarcomeres to shorten. The automatic contraction of fibrils in the muscle cells causes the characteristic muscle stiffness. In addition, the oxygen-deprived cells switch to glycogen as an energy source, converting it to lactic acid, the build-up of which causes the pH to fall from approximately 7.0 to 5.8 The perception of a meat’s juiciness or dryness depends on the binding of water to muscle proteins, and this is influenced by pH. Water-holding capacity is best in meats with a pH of 5.8.

The following problems, which decrease the quality of meat, can occur if rigor mortis is not properly managed:

• Dark-cutting beef
• Pale, soft, and exudative (PSE) pork
• Thaw rigor
• Cold shortening

If glycogen stores are depleted before death because the animal is exercised or stressed, insufficient lactic acid will be produced during rigor mortis. The resulting higher pH (above 5.8) of the meat will result in a deep-purple-brown meat known as dark-cutting beef, which has a sticky texture that is unacceptable to consumers. Unacceptable, pale, soft, and exudatinve pork results if the pH drops too low. A low pH - under 5.1, or even up to 5.4 - can cause the pork to become extremely pale, mushy, slimy, flavorless, and full of excess drip. Freezing meat before it undergoes rigor mortis cause thaw rigor, a phenomenon in which the meat shrinks violently by almost 50 percent when thawed. The same thing occurs, though to a lesser degree, when meat has been chilled too rapidly before rigor mortis, resulting in cold shortening. In both cases, the meat will be tougher. Neither thaw rigor nor cold shortening meat are allowed to be sold at the consumer level. Also, meat that is cooked while in a state of rigor mortis, called green meat or cooked rigor, will be tough. If it is prepared before stiffening begins, however, it can be quite tender.