Effect of ultrasound and temperature on tomato peroxidase

Tomato peroxidase (POD) was inactivated by heat and ultrasound. Thermal inactivation of tomato POD was performed at temperatures of 63, 64, 65, 66 and 67°C. Thermal inactivation of POD in tomato showed apparent first-order kinetics. E(a) was calculated from the slopes of Arrhenius plot and found as 14.9×10(4) J/mol. The effect of ultrasound on tomato peroxidase inactivation was investigated at 15%, 25%, 40%, 50% and 75% ultrasonic powers for 20-150 s. It was observed that as the ultrasonic power increased, inactivation rate increased. 100% POD inactivation was observed at 50% power for 150 s and at 75% power for 90 s of ultrasonication. Regeneration of POD activity was investigated for the samples exposed to ultrasound at different ultrasonic powers. It was observed that at 15% and 25% ultrasonic powers, residual enzyme activity increased linearly, whereas at powers of 40%, 50% and 75% residual enzyme activity increased nonlinearly. There was no regeneration in the samples which 100% enzyme inactivation obtained by ultrasound. A significant decrease in vitamin C content of tomato extract was observed as a function of temperature and treatment time, whereas ultrasonic treatment had no significant effect on vitamin C content of tomato extract.