To understand the conformational changes of mushroom PPO, the secondary structural change of the enzyme during thermosonication treatment at different power (60, 80 and 100%), temperature (20-60 degrees C) and time (0-30 min) combinations was investigated by using FTIR spectroscopy and compared with the change in enzyme activity. The enzyme inactivation higher than 99% was obtained at 100% amplitude at 60 degrees C for 10 min. FTIR studies showed that marked spectral changes were noted after ultrasound treatment at 20 degrees C. The alpha-helix and beta-sheet contents decreased, while aggregated beta p-sheet, turns and random coil contents increased as temperature increased up to 60 degrees C during thermosonication treatment for 10 min indicating protein denaturation. Aggregated bands located at 1683 and 1616 cm(-1) became evident after ultrasound treatment at 40 degrees C. When temperature was lowered back to 25 degrees C, from ultrasound treatment at 60 degrees C, these bands were still observed, indicating the irreversible change in the structure. (C) 2016 Elsevier Ltd. All rights reserved.