Meat pH and Pork Quality

pH has a high influence on water holding capacity (WHC), which is closely related to product yield and pork quality. WHC is the ability of meat to retain its water during processing, storage and cooking. Low WHC often results in high drip loss and poor eating quality (dryer and tougher in the cooked state). Water loss means a loss of saleable product yield. In extreme cases, this weight loss could reach as high as 10% or more. In addition, pork with low WHC does not hold a cure as well, a fact troubling to processors.

pH affects the color of pork. A low meat pH is often associated with low WHC and pale meat color. While high meat pH often causes a dark meat color, both pale and dark colors are unattractive pork colors to consumers. In addition, pork with pale color and low pH often has a metallic and off-flavor taste. Conversely, dark pork is high in pH and has a shorter shelf life than the normal reddish-pink colour that consumers prefer their fresh pork to be.

Changes in meat pH result from post mortem metabolism (glycolysis) and the conversion of glycogen into lactic acid. Variation in the rate and/or the extent of post mortem glycolysis is responsible for a major proportion of the variation in meat WHC and color. Pork with normal color and WHC reaches an ultimate pH of 5.6 to 5.7 within approximately 3 to 5 hours after slaughter. In contrast, Pale, Soft and Exudative (PSE) pork is caused by a very rapid drop in pH immediately after slaughter while muscle temperatures are still high. This combination of relatively low pH and high temperature results in proteins being denatured, which reduces WHC and results in a pale color. On the other hand, high meat pH (above 6.0 to 6.2) often causes dark, firm and dry (DFD) pork.

Low WHC and pale color often result from a rapid drop in ultimate meat pH which is triggered by a combination of a number of factors, such as genetics, pre-slaughter stress and post-slaughter handling. While the DFD condition results from low glycogen levels in the muscle at slaughter due to glycogen depletion that occurs from a combination of chronic stress and activity levels before slaughter.

Two genetic defects associated with low meat pH are Halohane and Rendement Napole (RN) genes. It is well known that pigs that carry the Halohane gene produce more PSE. Pigs that carry the RN gene can cause acid meat, which results from a more extensive decline in muscle pH and an abnormally low ultimate pH in the muscle. In appearance, acid meat is very like PSE meat, being pale and having a low WHC.

Preslaughter stress plays an important role on pork quality. Pork quality can be severely damaged during the last five minutes prior to stunning. PSE increases if hogs are handled roughly prior to slaughter. Pork quality can be improved by taking the following measures:

The outmost consideration after slaughter is to cool the carcass or muscles down as early and as fast as possible. Poor chilling at the slaughter plant increases PSE.