Secondary structure and conformational change of mushroom polyphenol oxidase during thermosonication treatment by using FTIR spectroscopy

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 °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 °C for 10 min. FTIR studies showed that marked spectral changes were noted after ultrasound treatment at 20 °C. The α-helix and β-sheet contents decreased, while aggregated β-sheet, turns and random coil contents increased as temperature increased up to 60 °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 °C. When temperature was lowered back to 25 °C, from ultrasound treatment at 60 °C, these bands were still observed, indicating the irreversible change in the structure.