★ We compared five methods for determining sound velocity in biological materials on example of pork. ★ We found that choice of method for determining sound velocity significantly influences the results. ★ The most accurate results were received by methods that used samples with two different thicknesses. ★ Sound velocity in pork at post-storage, room and vital temperatures ranged between 1555 and 1623 m/s.
Non-destructive ultrasonic methods for testing biological materials are applied in medicine as well as in food engineering to determine the physical parameters and the quality of agricultural products and raw materials such as meat. The purpose of this work was to identify the simplest and the most accurate of five methods for sound velocity determination across the fibers of the porcine longissimus dorsi muscle. The through-transmission technique (TT) was used for ultrasound signal acquisition with 2 MHz transducers. The first two methods (M1, M2) are based on the acquisition of a single ultrasound signal in the analyzed material, another two methods (M3, M4) rely on the acquisition of two ultrasound signals in samples with different thicknesses (two-distance method) and the last method (M5) involves the acquisition of a single ultrasound signal in the analyzed material and the acquisition of a single ultrasound signal in distilled water at the same distance between ultrasonic transducers (relative method). The results were processed by the nonparametric Kruskal–Wallis test and compared with published data. The mean values of sound velocity obtained with the use of the above methods in pork samples at post-storage, room and vital temperatures were as follows: method M1-1549.2/1581.7/1597.4 m/s, method M2-1477.7/1509.8/1597.4 m/s, method M3-1552.0/1599.0/1623.3 m/s, method M4-1557.4/1598.3/1623.6 m/s, method M5-1554.3/1583.7/1598 m/s. The experiment indicates that the choice of method for determining sound velocity significantly influences the results. Two of the five analyzed methods (namely M3 and M4), which involved measurements of the time of sound wave propagation through samples of the same material with varied thickness, produced velocity values most consistent with published data.