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 mu m; 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 mu W 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 degrees 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. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.