Energy density and mode of ultrasound application in fresh cow milk: Microbiological, physicochemical, and techno-functional properties

This study aimed to evaluate the application of different energy densities of high-intensity ultrasound (HIUS) on fresh cow's milk's microbial, physicochemical, and techno-functional properties. The samples were subjected to energy densities of 0.1 to 0.5 kJ/mL, at 24 kHz and 20 ± 1 °C, under continuous or pulsed mode. Raw and pasteurized milk (65 °C for 30 min) were used as control samples for comparison. The total surviving population of viable mesophilic aerobes (VMA) and total coliforms (TC); as well as the titratable acidity, pH, CIEL*a*b* colour, solids syneresis, viscosity, whey turbidity, and rennet sensitivity were measured. It was found that the mode of ultrasound application (continuous or pulsed) did not modify the milk’s microbial, physicochemical, or techno-functional response, except in the case of solids syneresis, where the solids solubility increased during continuous application. As the level of energy density increased, the reductions of VMA and TC, acidity, solids solubility, colour changes, and whey turbidity increased. In contrast, there were no effects on pH, viscosity, or rennet sensitivity. In conclusion, it was demonstrated that higher ultrasound energy densities cause intermediate microbial reductions (regarding conventional pasteurization, it was similar for VMA but lower for TC) without a negative impact on physicochemical and techno-functional properties, which can be correlated with different changes in the fresh milk macro components.