Effects of ultrasound treatment on stability of cocoa-flavored milk

Prevention of physical instability of chocolate milk is an important challenge in the field of food science, particularly dairy technolohy. In this study, the effects of high-intensity ultrasound treatment on stability of cocoa particles in chocolate milk, with or without the presence of stabilizers, was investigated. Chocolate milk was exposed to ultrasound (maximal nominal power 600 W at 20 kHz) at various levels of power intensity (24, 72 and 120 W), exposure times (2, 6 and 10 minutes) and temperatures (25, 45 and 65ºC) for 30 days. κ-carrageenan at concentrations of 0.000, 0.010, 0.015 and 0.020 %, with or without sugar (7.0% and 0.0%), was added to the samples. Increasing power intensity and exposure time led to a significant increase in physical stability of the milk samples − the milk phase volume decreased and the cacao phase increased. Moreover, the phase separation and cacao particle sedimentation were effectively prevented in the treated samples (ultrasonic power 120W, exposure time 2 min, temperature 45ºC, κ-carrageenan 0.02%, and sugar 7%) after 30 days of storage at 4ºC, while phase separation and cacao particle sedimentation occurred in the control sample (containing 0.040% κ-carrageenan). The findings also showed that sugar improved cacao milk stability. The milk phase volume in the presence of 0.02% κ-carrageenan, kept at a temperature of 45 ºC for 30 days, was less than that of samples kept at other temperatures. Based on the findings of the present study, it seems that ultrasound can increase the stability of cacao particles in milk. In addition, ultrasound treatment possibly degrades the κ-carrageenan network, particularly at higher temperatures. Furthermore, cavitation, probably due to entrapment of air in the κ-carrageenan network, may weaken the gel network