High-intensity ultrasound was used to investigate the inactivation of microorganisms in raw bovine milk. Raw bovine milk with 4% of milk fat was treated with ultrasonic probe that was 12 mm in diameter and with 20 kHz frequency immerged in milk directly. In the ultrasound treatment, three parameters were varied according to the statistical experimental design. The centre composite design was used to design and optimise the experimental parameters: temperature (20, 40, and 60°C), amplitude (120, 90, and 60 µm), and time (6, 9, and 12 min). All analyses were performed immediately after sonication and after 3 days and 5 days of storage under refrigeration at 4°C. The factors that seem to affect substantially the inactivation of microorganisms in using ultrasound are the amplitude of the ultrasonic waves, the exposure/contact time with the microorganisms, and the temperature of the treatment. The results achieved indicate a significant inactivation of microorganisms under longer periods of the treatment with ultrasonic probe, particularly in combination of higher temperature and amplitude. The output optimal value of total bacteria count was defined by Statgraphics where the lowest bacteria count was 3.688 log CFU/ml for the following specific ultrasound parameters: amplitude 120 μm, treatment time 9.84 min, and temperature 45.34°C.  

Research background. Two methods of milk treatment were used, ultrasound (innovative method) and bactofugation of milk, after which the physico-chemical and sensory properties of the milk were examined, with the primary aim of achieving consistency of the properties of the milk with pasteurization. Experimental approach. Ultrasound power levels of 200 and 400 W and frequency of 24 kHz with constant cycle were used. Milk treatment duration was 2.5, 5, 7.5 and 10 min with sonification at temperature of 20 °C (room temperature) and thermosonification (ultrasound at temperature higher than room temperature) at temperature of 55 °C. The purpose of this study was to investigate application of high power ultrasound, combined with a slightly increased temperature on: whole cow milk; skimmed cow milk and skimmed cow milk that passed bactofugation process. Results and conclusions. The best sensory grade was achieved when milk was treated with ultrasound power of 200 W, at 20 °C and the processing time was max. 7.5 min. This research shows potential of applications of high-power ultrasound in dairy industry, when combined with bactofugation technology as a pre-treatment for milk and with a slightly increased temperature (up to 55 °C). Novelty and scientific contribution. The application of these two technologies leads to milder processing conditions than pasteurization, an economical and more environmentally friendly technological process preferred by costumers and consumers, but also to a nutritionally beneficial composition of milk.

Research background. The application of high power ultrasound, combined with a slightly increased temperature on raw whole cow milk, skimmed cow milk, and skimmed cow milk that passed the bactofugation process were analyzed. A combination of those techniques, ultrasound and the bactofugation of milk was conducted to achieve the microbiological accuracy that is usually achieved by the pasteurization process. Experimental approach. The milk samples (200 mL) were treated for 2.5, 5, 7.5 and 10 minutes with high-power ultrasound (200 W and 400 W) with a frequency of 24 kHz. The treatments were conducted with a constant duty cycle of 100 %. Temperature levels during the treatments were 20 °C, and 55 °C. The count of somatic cells was analyzed for the aerobic mesophilic bacteria, as well the number of Enterobacteriaceae, Escherichia coli, and Staphylococcus aureus cells. Results and conclusions. The best result from the perspective of the reduction of the total count of bacteria was achieved by high-power ultrasound with a power of 400 W treated for 10 minutes. High reduction of Enterobacteriaceae, E. coli, and S. aureus cells was achieved in ultrasound treatment of raw whole, skimmed, and skimmed cow milk with a power of 200 and 400 W regardless of a treatment time. Novelty and scientific contribution: High-power ultrasound with a combination of bactofugation as a pretreatment for milk and with a slightly increased temperature (up to 55 °C) is much more economical than the pasteurization process, while it preserves the sensory and physical-chemical properties of milk.