Biochemistry of Pork Muscle Structure. 1. Rate of Anaerobic Glycolysis and Temperature Change versus the Apparent Structure of Muscle Tissue^a

Abstract

SUMMARY Continuous recordings of pH and temperature changes, during postmortem chilling, were made on 20 Danish Landrace carcasses. The continuous recordings from these carcasses depicted at least four distinct types of post‐mortem pH patterns: 1) a slow gradual decrease to an ultimate pH of 5.7–6.3; 2) a gradual decrease to about 5.7 at 8 hr, with an ultimate pH of 5.3–5.7; 3) a relatively rapid decrease to about 5.5 at 3 hr, with an ultimate pH of 5.3–5.6; 4) a sharp, significant decrease to a pH of about 5.1 at 11/2 hr, and a subsequent elevation to 5.3–5.6. The first 3 types were acceptable in structure, color, and water retention, whereas type 4 represented pale, exudative tissue with soft, inferior structure. The violent nature of the post‐mortem changes in tissue with the type 4 pH pattern were discussed, as well as the possibility of a more rapid onset of rigor mortis in this tissue. Although the pH values of the pale, exudative tissue were elevated during chilling, it appeared that they remained generally lower, ultimately, than the normal tissue. On the basis of comparisons between muscles, it is suggested that in addition to chemical composition, the chilling rate of the individual muscle may also be an important factor in determining pH pattern and ultimate muscle structure.

Effects of Rhus coriaria on nutrient composition, thiobarbituric acid reactive substances and colour of thigh meat in heat-stressed broilers

“…Muscle pH variation is also related to glycogenolysis, and increased catecholamine secretion in response to an acute stressor just prior to slaughter. Increased glycogen breakdown lowers the pH post slaughter (Briskey & Wismer-Pedersen, 1961). The pH decline of meat after slaughter is higher during heat stress conditions (Feng et al, 2006).…”

“…Lipid oxidation is a major cause of muscle quality deterioration and can directly affect quality characteristics such as flavour, colour, texture, nutritive value and safety of the meat (Buckley et al, 1995). Normally, pH declines gradually from 7.4 in living muscle to roughly 5.6 -5.7 within 6 -8 h post mortem, and then has an ultimate pH at 24 h of about 5.3 -5.7 (Briskey & Wismer-Pedersen, 1961). A number of studies have demonstrated the effects of heat stress on increased reactive oxygen species (ROS) production and oxidative damage to skeletal muscle of chickens (Mujahid et al, 2009).…”

The buffering capacity of porcine muscles

“…Because light muscles are more glycolytic than dark ones (Briskey & Wismer-Pedersen, 1961;Merkel, 1971;Lundström, Essén-Gustavsson, Rundgren, Edfors-Lilja & Malmfors, 1989;Warner, Kauffman & Russell, 1993), it can be assumed that there is already more lactic acid in living light muscle than in dark muscle. This would induce a problem because all muscles consist of light and dark muscle fibres, and an existence of a pH gradient between light and dark fibres would not be energetically favourable and would lead to ion exchange.…”

“…As a result of post-mortem metabolism, glycogen and ATP levels decline, and lactic acid accumulates in the muscle. This lowers the muscle pH (Kastenschmidt, Hoekstra & Briskey, 1968) and results in an ultimate pH of about 5.4 to 5.7 at 24 h in porcine longissimus dorsi muscle (Briskey & Wismer-Pedersen, 1961). The amount of glycogen present in the muscle will determine the extent of the pH decrease, but only if the glycogen concentration in pig muscles has decreased to values below 53 mmol/kg wet weight in the living animal (Henckel, Karlsson, Jensen, Oksbjerg, & Petersen, 2002).…”

Prediction of Japanese color score

“…It is characterized by the lowering of muscle pH due to the accumulation of lactic acid within the muscle. Normal glycolysis continues in muscles until either glycogen levels are depleted or a low muscle pH (approximately 5.4 to 5.5) is reached within 6 to 12 h, whereas the completion of rigor occurs within 4 to 6 h (Briskey and Wismer-Pedersen, 1961). Low pH (< 5.4) causes the inactivation of many enzymes affecting the breakdown of glycogen, ceasing the ability to produce ATP (Hedrick et al, 1994;Sahlin et al, 1978).…”