After slaughter oxygen supply to muscle is stopped so glycogen is metabolized following anaerobic pathways, aiming to generate the needed ATP for keeping the equilibrium in the muscle cell. As consequence energy sources (creatine phosphate, glycogen, glucose, ATP, ADP and AMP) are depleted and lactic acid (from glycogen) and hypoxanthine (from ATP) are produced. Lactate is accumulated leading to a drop in the pH of the muscle. The ability of the muscle to generate post-mortem energy is known as glycolytic potential and can be determined by measuring the content of glycogen, glucose, glucose-6-P and lactate. A direct relation exists between the rate of lactic acid production, the final amount of lactic acid, final pH of meat and the meat quality. Fast lactate production and final low pH are commonly related with PSE (pale, soft and exudative) meat; when low rates of lactate production and high final pH are observed DFD (dark, firm and dry) meat is obtained; both are considered as low quality meat. A correct glycolytic potential along with adequate glycolysis ratio determine the final quality of the meat. Initial amount of glycogen and the rate of conversion into lactate will determine the quality of the meal. 

[1] Ferguson D, Daly B, Gardner G, Tume R. Effect of glycogen concentration and form on the response to electrical stimulation and rate of post-mortem glycolysis in ovine muscle. Meat science 2008;78:202-10.

[2] Scheffler T, Rosser A, Kasten S, Scheffler J, Gerrard D. Use of dietary supplementation with β-guanidinopropionic acid to alter the muscle phosphagen system, postmortem metabolism, and pork quality. Meat science 2013;95:264-71.

[3] England EM, Matarneh SK, Scheffler TL, Wachet C, Gerrard DE. Altered AMP deaminase activity may extend postmortem glycolysis. Meat science 2015;102:8-14.

[4] Choe JH, Choi YM, Lee SH, Shin HG, Ryu YC, Hong KC, et al. The relation between glycogen, lactate content and muscle fiber type composition, and their influence on postmortem glycolytic rate and pork quality. Meat science 2008;80:355-62.

[5] Apaoblaza A, Galaz A, Strobel P, Ramírez-Reveco A, Jeréz-Timaure N, Gallo C. Glycolytic potential and activity of adenosine monophosphate kinase (AMPK), glycogen phosphorylase (GP) and glycogen debranching enzyme (GDE) in steer carcasses with normal (5.9) 24 H pH determined in M. longissimus dorsi. Meat science 2015;101:83-9.

[6] Henckel P, Karlsson A, Jensen MT, Oksbjerg N, Petersen JS. Metabolic conditions in Porcine longissimus muscle immediately pre-slaughter and its influence on peri- and post mortem energy metabolism. Meat science 2002;62:145-55.

You read any meat science book for this basic query.

The main factors which affect t the sensory quality of meat as general include; the type of meat, warmed-over flavour, production and rearing conditions and postmortem practices. However, there are many other factors which have effects including Genotype which affects juiciness, tenderness, acidulous taste , sex which affects  juiciness and acidulous taste, a prolongation in ageing time which affects the colour and  taste intensity.

 In addition to the different answers, the Endogenous bacteria of meat and its metabolites  play an important  role in meat quality.

Postmortem treatments - aging processing condition like temperature and RH; method of slaughtering; health of the animal pre-slaughter, etc.

Thank you so much to all who shared the added information especially that of Mr. Carlos Alvarez.. thank you sir..

The factors affecting the quality of meat are different, the most important of which are microbiological factors, microbes, fungi, physical factors such as cooling, freezing and chemical factors.

Quality of meat is affected by the genetic propensity of the animal, how the animal is reared, and the nutritional status during production. These factors affect the fat, lean and connective tissue component of meat and therefore influence meat quality.

Short-term acute stress, such as excitement or fighting immediately prior to slaughter, produced lactic acid from the breakdown of glycogen. This results in meat which has a lower pH, lighter color, reduced water binding capacity, and is possibly tougher.