Measurement of the acoustic phase velocity of trade butters by means of the ultrasonic transmission technique

There are different methods and ways to measure the internal properties of materials; this depends on the type of material and the grade of precision and resolution that is desired. In the case of food, there are different instruments to determine its quality, focussing on the main factors such as colour, texture, smell, flavour, pH, and microbial charge. In this work, a study is presented to determine the acoustic phase velocity of trade butter from the LALA® and Gloria® brands. The GAMPT acoustic tomography echoscope stage with 2MHz acoustic sensors was used to measure the thickness-dependent acoustic phase velocity [m/s] with a quasi-regular ambient temperature of 16°C. The method applied was the transmission technique with normal incidence. Measurements were performed in triplicate. The bulk density and acoustic impedance of the butter samples, as well as the rheological properties, were determined by indirect methods. The results show that the acoustic phase velocity of butter LALA®, Gloria® with salt, and Gloria® without salt were, APVLALA ≈ 1055.54m/s, APVGLORIAws ≈ 1224.46m/s, and APVGLORIAns ≈ 1169.44m/s, respectively. The bulk densities of the butters were rLALA ≈ 908.67gr/cm3, rGLORIAws ≈ 771.79gr/cm3, and rGLORIAns ≈ 825.57gr/cm3 at 15°C, respectively. Transmittance was evaluated as a function of frequency, where the effect of attenuation was observed and described as the thickness of the samples increased. However, the acoustic impedance was similar between the different types of butter samples, and this is because the acoustic phase velocity was different, but the product times the bulk density was compensated for, that is, GLORIA butter with salt presented a higher acoustic phase but lower density; on the contrary, LALA butter had the lowest acoustic phase velocity, but the bulk density was higher.