Effect of photosonication treatment on inactivation of total and coliform bacteria in milk

The combined effect of simultaneously applied acoustic energy and ultraviolet irradiation (UV-C), named photosonication, on the population reduction of total and coliform bacteria in raw milk was investigated. Photosonication was carried out at 100% (120 μm; 240 W) amplitude of ultrasound accompanied by UV light of 13.2 W cm-2 while sonication was carried out at 100% amplitude without UV light. An ultrasonic processor (400 W and 24 kHz with a 22 mm diameter probe) and 3 ultraviolet lamps (4400 μW cm-2 per lamp) were used. The exposure time was 15 min for all treatment, and samples were taken after 0, 3, 6, 9, 12 and 15 min. Thermal treatment (at 65 °C for 30 min) achieved a 3.29 log and 5.31 log-reduction for total and coliform bacteria, respectively. However, the reduction achieved was 4.79 log cfu mL-1 and 5.31 log cfu mL-1 for total and coliform bacteria, respectively, in photosonication while 1.31 log cfu mL-1 and 4.01 log cfu mL-1 for total and coliform bacteria, respectively in sonication. During photosonication, UV light contributed to an increase of lethality.