Effects Of Electrical Stimulation And Delay Chilling On Calpain System Activities And The Tenderness Of Bovine M.longissimus

Tenderness is the most important beef palatability. Except for physiological factors including breeds and years, post-slaughter handling such as electrical stimulation and chilling system play important roles in meat tenderization. Many scholars had proved that the potease calpains were the result of the tenderness of beef improved. Based on preceding researches, this experiment analysised the effects of delay chilling and electrical stimulation on calpain system activities and the tenderness of bovine M. longissimus of Chinese Yellow crossbred bulls by measuring calpain system activities, pH, temperature and shear force values in the processes of beef aging. The mechanism of beef aging were studied through effects of delay chilling and electrical stimulation on calpain system activities, pH, temperature and shear force values and also provided theoretical basis to improve beef palatability by the experiment.The major results of the experiments are as follows:Part 1 Effects of delay chilling and electrical stimulation on beef palatabilityThe results indicated that delay chilling decelerated the rate of carcass temperature decline, whereas electrical stimulation had no significant effect on the rate of carcass temperature decline. Both delay chilling and electrical stimulation increased the rate of pH decline significantly. Moreover, carcass temperature showed a positive correlation with pH. At 24h, 72h, 168h, 240h postmortem aging, the shear force values of beef longissimus from delay chilling were lower than those from conventional chilling group by 18.25%, 12.11%, 13.47% and 11.03%; The shear force values of beef longissimus from electrical stimulation were lower than those from conventional chilling group by 23.15%, 14.0%, 21.38%, 18.01%. Electrical stimulation and delay chilling decreased the shear force values of beef longissimus(P<0.05).Part 2 Isolation and purification of calpain systemCalpains purified by DEAE-Sepharose-FF column were determined. The results showed that calpains were eluted at 2ml/min by a two-stage procedure consisting of a linear 0-215mMNaC1 gradient, and then followed by 215-500mMNaC1. Moreover, calpastatin,μ-calpain and m-calpain were separated by NaCl 25-125mM, 130-200mM and 230-330mM respectively.Part3 Effects of electrical stimulation and delay chilling onμ-calpain activities of beef longgissimusIn this experiment, both delay chilling and electrical stimulation increasedμ-calpain activities compared with conventional chilling after postmortem aging 1h significantly (P<0.05).Subsequently,μ-calpain activities from beef longgissimus decreased swiftly.μ-calpain activities from delay chilling group were lower than those from conventional chilling by15.6% and 45.4% at postmortem aging 24h and 72h;μ-calpain activities from electrical stimulation group were lower than those from conventional chilling by 40.5% and 68.8% at postmortem aging 24h and 72h. Both electrical stimulation and delay chilling decreased the levels ofμ-calpain significantly (P<0.01);μ-calpain activities were not detected from different groups at postmortem aging 168h. The results showed that both delay chilling and electrical stimulation improvedμ-calpain activities significantly (P<0.05) and enhanced the tenderness of bovine M. longissimus during earlier aging periods compared with conventional chilling. But in later aging periods, both delay chilling and electrical stimulation weakened the effect on the tenderness of beef because of premature consumption ofμ-calpain.Part4 Effects of electrical stimulation and delay chilling on m-calpain activities of beef longgissimusBoth delay chilling and electrical stimulation increased the activities of m-calpain compared with conventional chilling after postmortem aging 1h significantly (P<0.05); Subsequently, m-calpain activities from beef longgissimus also decreased significantly. However, m-calpain activities from delay chilling group and electrical stimulation group had no significant differences from conventional chilling. These showed that both electrical stimulation and delay chilling had no significant effects on m-calpain activities and that m-calpain didn't play an major role in the course of postmortem aging.Part5 Effects of electrical stimulation and delay chilling on calpastatin activities of beef longgissimusCalpastatin activities from delay chilling group and electrical stimulation group were higher than those from conventional chilling by 27.9% and 39.3% respectively. Both delay chilling and electrical stimulation had significant effects on calpastatin activities (P<0.05); But subsequently, the activities of calpastatin from beef longgissimus also decreased significantly. Calpastatin activities from delay chilling group were lower than those from conventional chilling by17.3% and 41.4% at postmortem aging 24h and 3d; Calpastatin activities from electrical stimulation group were lower than those from conventional chilling by 25.2% and 71.8% at 24h and 72h of postmortem aging. Both electrical stimulation and delay chilling decreased the levels of calpastatin significantly (P<0.01); Calpastatin activities were not detected from different groups at 168h of postmortem aging. The results showed that both delay chilling and electrical stimulation increased the rate of calpastatin activities decline significantly, reduced the inhibition of calpastatin onμ-calpain and had a positive effect on the postmortem aging of beef.Part 6 Effects of electrical stimulation & delay chilling on calpain system activities and beef palatabilityThe results showed that ES&DC had a significant effect on the rate of pH decline, carcass temperature, shear force values,μ-calpain and calpastatin activities of beef than electrical stimulation. However, ES&DC had no significant effects on m-calpain activities. These showed that electrical stimulation had a significant correlation with chilling system.