If stimulated by stress factors before slaughter, muscle energy level will be very high after slaughter, muscle will undergo anaerobic glycolysis, and acid metabolites such as lactic acid and phosphoric acid will accumulate rapidly in muscle, which will lead to a sharp drop in pH value after slaughter, poor water retention capacity of muscle, extravasation of juice, and pale meat color, resulting in PSE (pale, soft and vented) meat. If it is stimulated for a long time before slaughter, the muscle energy level is low, the muscle tissue lacks glycogen and undergoes anaerobic glycolysis, and the acid metabolites are few, so that the pH value is maintained at a high level for a certain period after slaughter, and the muscle is dry, hard and black (black, solid, dry and DFD meat).
The level of glycogen in muscle before slaughter is high and the activity of starch branching enzyme is strong. After slaughter, the ability of muscle to convert glycogen into lactic acid is improved, which leads to low terminal pH value, lower protein content in muscle and lower water retention, thus affecting processing yield.
Figure 26 Evaluation and grading of pork