Abstract
The purpose of this research was to study whether pulsed electric fields (PEFs) could reduce variability in the activity and thermostability of ascorbic acid oxidase (AAO) in the pur,e of different carrot cultivars, i.e. Daucus carota cv. Nantes, White Belgian, Solar Yellow, Nutri Red and Purple Haze. The carrot pur,e was treated at different energy inputs (35 and 300 kJ/kg) and electric field strengths (0.3, 0.5 and 0.8 kV/cm). AAO catalytic kinetics was described using the Michaelis-Menten model to estimate V (max) and K (M) . The catalytic kinetics of AAO varied greatly depending on cultivar with the highest V (max) in White Belgian and the lowest V (max) in Nantes. Energy input of 300 kJ/kg significantly (p < 0.05) reduced the V (max) in White Belgian and Yellow Solar and increased the K (M) in Nantes and Nutri Red. A first-order reaction model was used to describe AAO thermal inactivation kinetics (60-70 A degrees C) and to estimate the inactivation rate constant (k) at a reference temperature of 65 A degrees C (k (ref) ) and the temperature dependency of k (E (a) ). AAO in Purple Haze was found to have the lowest E (a) and the highest k (ref) , while the highest E (a) was observed in Yellow Solar and the lowest k (ref) in Nantes. This study demonstrated that PEF treatment at various electric field strengths changed the thermostability of AAO. PEF treatment of 0.8 kV/cm and 35 kJ/kg reduced the variability of AAO thermostability in the pur,e of these different carrot cultivars and consequently narrowed the window of processing temperature and time combinations to achieve the same degree of AAO inactivation.