Effect of ultrasound alone or ultrasound coupled with CO2 on the chemical composition, cheese-making properties and sensory traits of raw milk

Abstract

This study aimed to evaluate the effects of different intensities and durations of ultrasound on the composition, oxidation, cheese-making properties and sensory traits of raw milk. Moreover, the effects of the addition of CO2 and HCl prior to the sonication were tested to determine whether these chemicals could reduce the production of off-flavours. Treating milk with ultrasound led to certain changes in milk composition. We observed significant increases in free fatty acid levels, oxidation, and decreases in somatic cell count and pH; improved coagulation traits were also observed. The results of sensory evaluations revealed a significant increase in a burnt off-flavour with increasing intensity and duration of the ultrasound treatment. The addition of CO2 appeared to significantly reduce the disruptive effect of ultrasound, the formation of oxidation products and the detection of the burnt off-flavour, whereas the sour flavour was increased. Among the new technologies that are used to improve milk sanitisation and shelf life, ultrasound treatment has been demonstrated to inactivate many bacterial species and to be a viable sanitisation procedure. In this study the milk coagulation properties of sonicated milk were dramatically improved following the ultrasound (US) treatments, indicating a possible use for US in the cheese-making industry. Moreover, despite the evident production of off-flavours caused by US in milk, the use of CO2 to reduce pyrolytic processes and thus the formation of oxidation products, appeared to be promising with respect to the increased use of sonication on food and other organic matrices.