Changes in calpain activity, protein degradation and microstructure of beef M. semitendinosus by the application of ultrasound.

In this investigation, samples were treated by ultrasonic probe (20 kHz) at an intensity of 25 W cm for 20 or 40 min, followed by aging at 4 °C for 1, 3 and 7 d. Ultrasound treatment significantly increased myofibrillar fragmentation index (MFI) and decreased Warner-Bratzler shear force (WBSF) at 3 and 7 d of postmortem aging (P < .05). Ultrasound-treated samples showed significantly greater intensities of autolyzed 76 kDa subunits and the lower intensity of intact 80 kDa form compared to control at 1 d of storage (P < .05). Significant difference was found between semitendinosus (ST) samples treated for both 20 and 40 min (P < .05). Ultrasound treated samples showed increased proteolysis during the postmortem storage as reflected by an increased degradation of desmin and troponin-T. These results showed that ultrasound treatment could improve the tenderness of beef ST muscle through regulating the calpain activation and protein degradation during postmortem aging.