LAUSR

The effects of ultrasound (0, 300 and 600 W for 20 min at the frequency of 20 kHz) followed by postmortem aging (0, 4 and 8 d aging time) on beef quality were evaluated. Ultrasound treatment, aging time and their interaction all significantly affected the pH and tenderness of beef (p < 0.05). Furthermore, ultrasound improved the cathepsin B + L activities and the solubility of collagen compared with the control without ultrasound treatment (p < 0.05). In terms of microstructure, the perimysium was ruptured by the ultrasound treatment which caused the collagen fibers to be disorderly and loosely arranged. In addition, ultrasound could affect the structural stability of collagen resulting in a significant reduction of thermal denaturation temperature (p < 0.05). The results showed that ultrasound could improve beef tenderness during postmortem aging by changing collagen structure and regulating the activities of cathepsin B + L.