Abstract: The inactivation kinetics of polygalacturonase (PG) after heat and ultrasonic treatments were investigated. PG activity was determined by colorimetry using 3,5-dinitrosalicylic acid. The results indicated that PG was not obviously inactivated by heat ( ≤ 45 ℃) or ultrasonic treatment alone (20 kHz; 0 ℃; 242, 605 or 968 W/cm2 power density), retaining more than 80% of its original activity. The activity of PG was almost constant after 15 min of heat or ultrasonic treatment. The inactivation curve was well fitted with a partial transformation model. PG was significantly inactivated by combined heat (25–45 ℃) and ultrasonic treatment and the inactivation curve was fitted with a first-order kinetic model. The activity of PG was decreased to 13.72% by ultrasonic treatment at 20 kHz, 35 ℃ and 605 W/cm2 power density for 16 min. However, neither heat treatment (35 ℃ for 5 min) followed by ultrasonic treatment (605 W/cm2 power density and 0 ℃ for 0–10 min) nor the reverse sequence (ultrasonic treatment for 5 min and subsequent heat treatment for 0–10 min) inactivated PG, indicating that ultrasonic and heat treatment could inactivate synergistically PG only when they were simultaneously carried out. The results from this study can provide theoretical data for the inactivation of PG by ultrasonic treatment in fruit and vegetable juice processing.

Key words: polygalacturonase, heat treatment, ultrasonic treatment, synergistic effect, kinetics