ATTENUATION OF ULTRASOUND IN MILKS AND CREAMS

Measurements of the attenuation of 1.5 to 7 MHz ultrasound in milks and creams, aqueous solutions of milk proteins and milk fat demonstrated that the attenuation due to the fat component was proportional to the fat concentration (at low volume fractions, less than 4%) and was caused by two effects: losses arising from its particulate nature and intrinsic attenuation (mass attenuation coefficient 1.1 cm2 g-1 at 7 MHz in pure milk fat). Comparison with theoretical equations showed that absorption by thermal conduction dominated the particulate losses and increased with decreasing fat globule size, over the range 1.5 to 7 MHz. This was confirmed by examining milks homogenized to different degrees. The losses in the non-fat components were mainly due to the protein components which also probably dominated the shape of the attenuation titration curves for skimmed milk, producing peaks in attenuation in the range pH 4-4.5 and about pH 11.3. © 1990.