Inactivation mechanism of polyphenol oxidase during ultrasound treatment

Baltacıoğlu, Hande
In this study, the activity and conformational changes of mushroom polyphenol oxidase (PPO) were investigated during the inactivation by heat-ultrasound treatment at different power, temperature and time combinations. The secondary structure change of the enzyme during inactivation was analyzed by using Fourier Transform Infrared (FTIR) spectroscopy and compared with the enzyme activity change. In thermosonication (TS) treatment, the residual enzyme activity decreased with increasing power, time and temperature. The enzyme inactivation higher than 99 % was obtained at 100 % amplitude at 60 °C for 10 min. For comparison, when the stability of mushroom PPO after thermal treatment was investigated, approximately 99% inactivation was obtained at 70 °C for 5 min. D value for thermal treatment at 60°C was found as 6.66 min whereas for 100, 80 and 60 % amplitude TS treatments at the same temperature, D values were found as 2.09, 3.33 and 3.44 min, respectively. FTIR studies showed that the thermal and TS treatments caused an irreversible change on the secondary structure of the enzyme. α-helix and β-sheet content decreased, while aggregated β-sheet, turns and random coil content increased during the temperature increase. The transition temperature (Tm) values of TS and thermal treatments were 44 and 55 ºC, respectively. This result showed that heat and ultrasound combination behaved synergistically on the conformational change of the enzyme. Compared to the thermal treatment, TS treatment seemed to be more effective on the secondary structural change at lower temperatures.
Citation Formats
H. Baltacıoğlu, “Inactivation mechanism of polyphenol oxidase during ultrasound treatment,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.