Effects of high-intensity high-frequency ultrasound on ageing rate, ultrastructure and some physico-chemical properties of beef

High-intensity and high-frequency ultrasound was tested for its ability to accelerate meat ageing and increase beef tenderness. Samples (approximate t o 50 g) of semimembranosus muscles from 8 cull cows were assigned to ultras onic treatment (2.6 MHz; 10W/cm(2); 2 x15 s) either pre-rigor (day 0, pH 6. 2) or post-rigor (day 1, pH 5.4). When applied pre-rigor, ultrasound induce d a slight delay in rigor mortis onset, a stretching (12-15%) of the sarcom eres (p < 0.05), an ultrastructural alteration in the Z-line region and an immediate increase (around 30%) in the release of calcium in the cytosol (p < 0.05). However, no conclusive effect on meat ageing rate was observed. P ost-rigor ultrasonic treatment did not induce any structural modification b ut slightly improved the ageing index after 6 days (p<0.05). However, no im provement in the final (day 14) ageing index was observed compared to the c ontrols. As ultrasound had also no effect on the thermal stability of colla gen, at both postmortem times, no improvement in meat tenderness can be exp ected under the conditions used. (C) 1998 Elsevier Science Ltd. All rights reserved.