Effect Of Two-stage Chilling And Electrical Stimulation On Eating Quality And Myofibrillar Ultrastructural Of Beef

Tenderness is the most important factor to determine the beef quality, which determines the commercial value of meat products. Nowadays, the inconsistency and variability of beef tenderness are two major problems that meat industries face. To solve the problems, we must deeply understand the mechanism and their tender mechanism to produce the meat variability. Studies have suggested the postmortem treatments (the rate of cooling, electrical stimulation or not etc.) were important factors on beef tenderness. Based on previous researches, two group crossbreed yanbian×Simmental were butchered according to the standard processing with TC, CC , ES&CC and ES&TC treatment. The purpose of this research is to study the effect of electrical stimulation and two-stage chilling on tenderness of beef by analysis of carcass temperature,pH and shear force. By myofibril ultrastructure research, the effect of electrical stimulation on myofibril ultrastructure and the relation between shear force and sarcomere length were studied.In this study, the main results are as follows:Two-stage chilling had increased the rate of the carcass temperature drop, decreased the rate of pH drop, decreased evaporative loss of carcasses, helped to improve the color of beef, and increased shear force, but had no significant effect on water holding capacity of beef. ES&CC had increased the rate of pH drop, increased meat tenderness, but had no significant effect on carcass temperature and evaporative loss. ES&TC had complex role on the carcasses, increased the rate of temperature and pH drop, decreased evaporative loss of carcasses, and increased meat tenderness. Electrical stimulation and two-stage chilling had no significant effect on water holding capacity of the longest dorsal muscle.Through analysis of ultrastructure of the longest dorsal muscle, the results showed: two-stage chilling cause cold shrink, extended the process of the rigor mortis, decreased the recover rate of sarcomere length and the rate of meat tenderization. At 45min post-mortem, the sarcomere length of ES was 1.67μm, which shorter than the sarcomere length of NES. Electrical stimulation led to the occurrence of contractile zone, where sarcomere length decreased but muscle fiber increased. Sarcomeres around contractile zone were mechanically stretched. At 24 hour postmortem, the average sarcomere length of ES sample was 1.50μm, and 0.52μm for sarcomeres within contractile zone, whilst 1.89μm for sarcomres around contractile zone. At 3d postmortem, ES&CC and ES&TC had no contractile zone, this showed that the effect of ES was not obvious, and contractile zone formed during ES was attributed to partial ultracontraction of myofibrils. With the increase of aging time, tenderness was improved, sarcomere length and MFI value increased, and thus beef tenderness increased.Through this test , we can see there were relationship between sarcomere length and shear force when the correlation of pH and temperature is higher. Short sarcomere length stand for high shear stress values...