Effect of ultrasound an temperature on tomato peroxidase

Activity of tomato peroxidase (POD) was determined by using guaiacol and o-dianisidine as hydrogen donors. Activity of tomato POD for inactivation experiments was determined by using o-dianisidine as hydrogen donor because low Km (Michaelis-Menten constant) value was found by using o-dianisidine. Thermal inactivation of tomato POD was performed at temperatures of 63, 64, 65, 66 and 67 ? C. 50% reduction in POD activity was observed at 63, 64, 65, 66 and 67 ? C for 15.5, 10.5, 6.5, 5 and 3 minutes, respectively. The effect of ultrasound on tomato POD inactivation was performed at 15, 25, 40, 50 and 75% ultrasonic powers. It was observed that as the ultrasonic power increased, inactivation rate increased. 100% POD inactivation was observed at 50% and 75% powers for 150 and 90 seconds, respectively. Regeneration of tomato POD activity was investigated for the samples exposed to ultrasound at different ultrasonic powers (15, 25, 40, 50 and 75%) and stored at 4 ? C for one week period. It was observed that regeneration increased as the ultrasonic power increased. There was no regeneration in the samples which 100 % enzyme inactivation obtained by ultrasound. Vitamin C and total bacteria of tomato extract after heat and ultrasonic treatment were used for quality indicator. When approximately 50% POD was inactivated, vitamin C of tomato extract was decreased 27% by heat treatment and no reduction by ultrasonic treatment was observed. Higher amount of total bacteria reduction was observed by ultrasonic treatment.Key Words: Tomato, peroxidase, kinetics, heat, ultrasound, vitamin C.