Investigation of ultrasound processing for homogenisation of blackberry dairy-based beverages†

Ultrasound (US) processing is a novel technology that has many potential applications in food processing. Pilot-scale batch US homogenisation of a blackberry-enriched dairy beverage was investigated in this study. Particle size, apparent viscosity, colour, phenolic content and antioxidant activities of US homogenised beverages were compared to those of conventionally homogenised products. Blackberry powder was mixed with preheated whole milk (37 °C) at a ratio of 1 : 20 (w/v). The mixture was treated at an US intensity of 10.37 ± 0.58 W cm⁻² for selected treatment times of 1, 3 and 5 min, while the control sample was homogenised using a conventional homogeniser for 1 min at 10 000 rpm. US treatment resulted in smaller particle size compared to the control, and longer US treatment time increased the number of smaller particles (p < 0.05). A higher viscosity value was measured in all US-treated samples when compared to the untreated blackberry–milk beverage (p < 0.05). Minor significant changes in colour parameters of all US-treated samples were observed compared to the control (p < 0.05). The application of US treatment to blackberry–milk beverages resulted in comparable retention of phenolic contents and antioxidant activities compared to conventional homogenisation.