Effect Of Rapid Chilling And Electrical Stimulation On Beef Quality

Tenderness is the most important factor influencing consumer satisfaction for beef palatability. But beef tenderness does not meet the requirement of consumers for decrease in tenderness and increase in tenderness variation. So, how to increase beef tenderness and decrease variation in tenderness has become the hot topic in meat science.Conventional carcass chilling is a time-consuming and energy-expensive process, and increase extra microbial hazards and weight loss. Rapid chilling (RC) can improve production efficiency by decreasing the required chilling time, and also exploit the lower cooler shrink loss and inhibit microbial activity. However, previous studies indicate that raid chilling may decrease tenderness and increase the variation in tenderness, and have adverse effect on meat color, which influence consumer's satisfaction for beef palatability.Electrical stimulation (ES) was studied and applied industry since 1960. Lots of studies indicate that electrical stimulation can prevent cold short by accelerating the decent rate of pH value, and can induce the abnormal release of Ca⁺⁺ which can active calpains to accelerate proteolysis. It has been reported that ES can create physical damage to myofibril and increase beef tenderness. However, ES has not been used universally in the world and especially little in China. The validity and mechanism are also in research. Therefore, It has been an attractive question whether there is any improvement on beef palatability when RC is applied combined with ES.The article studied effects of RC and RC combined with ES on beef quality by cooking loss, tenderness, meat color, and the tenderrise mechanisms were investigated by analysis of cytoskeleton protein degradation and microstructure to prvide theroretical foundation to beef palatability.1. Effect of rapid chilling and electrical stimulation on M. longissimus quality.Two groups of cattle were selected to evaluate the effects of rapid chilling on beef quality. Fifty Yanbian yellow cattle crossbred bulls were randomly selected at the regular production line. After splitting the carcasses, rapid chilling was applied to one side of the carcasses, while conventional chilling was applied to the other one. Sides were weighed for cooler shrink loss determination at 24 h PM,.Twenty Yanbian yellow cattle crossbred bulls were selected and slaughtered according to standard process. RC: (-15±1℃for 2 h, air velocity of 3 m/s) then transferred into conventional chilling (CC) to 24 h PM. And CC was applied to left and right sides of the carcass after slaughtering. After 24 h in the conditioning room, the carcasses were transferred to the cutting room, and the M. longissimus were excised from the carcasses. A series of 2.54-cm-thick steaks were removed for cooking loss and tenderness determinations, which were vacuum packed and stored at 2±2℃until 7 d PM. Effects of RC and ES were determined by profiles of pH and temperature, meat color and shear force at 1d, 3d, 7d postmortem (PM). The steaks used for tenderness determinations were collected on 1 d, 3 d, and 7 d PM respectively, and all were frozen immediately at -30℃until assayed. Meat color were obtained at 1d, 3d, 7d PM, following a 20 min bloom period, color of the beef fresh cut was objectively evaluated by recording CIE L^*, a^*, and b^* values.The results showed that RC decreased evaporative loss significantly (p<0.05) by 15.2%. RC decreased carcass temperature and delayed pH decline, so the incidence of cold shoring increased. RC had no effect on cooking loss and meat color, but increased shear force at 1d, 3d (P<0.05). RC combined with ES increased pH decline, so decreased the danger of cold shorting. ES increased L^* value significantly, and decreased shear force at 1d, 3d and 7d. So RC combined ES could decrease the detrimental effect of RC while maintain the advantage of RC at the same time.2. Michanisms of RC and ES influenced M. longissimus tenderness.In order to evaluate the effects of RC and ES on cytoskeleton protein degradation and microstructure change, twenty Yanbian yellow cattle crossbred bulls were selected and randomly divided into two groups. One group was applied with ES, and another group was not stimulated refer to as non-stimulated control. RC(-15±1℃for 2 h, air velocity of 3 m/s, then transferred into conventional chilling to 24 h PM)and CC(0-4℃for 24 h) were applied to left and right sides of the carcasses respectively after slaughtering. After 24 h in the conditioning room, the carcasses were transferred to the cutting room, and the M. longissimus were excised from the carcasses. A series of samples were picked for SDS-PAGE, western blotting and transmission electron microscopy at 2h, 1d, 3d, 7d.The degradation of Troponin-T, Desmin, Nebulin, Titin and the ultrastructural changes were investigated.The results showed that the degradation rate of desmin and Troponin-T were decreased by RC, but were were accelerated by ES. The acceleration of cytoskeleton degradation was the reason ES accelerate aging. The degradation of Troponin-T and Nebulin were detected at 2 h PM, so Troponin-T and Nebulin act as indictor of aging. ES introduced physical damage to myofibril, and lots of contractile bands and stretched bands appeared. ES accelerated fracture of Z band and disappear of I bands, so physical destroy may be the main reason to increase beef tenderness.