Thermal inactivation kinetics of peroxidase and lipoxygenase from broccoli, green asparagus and carrots

Thermal inactivation curves for peroxidase (POD) and lipoxygenase (LOX) in broccoli (florets), green asparagus (tip and stem), and carrots (cortex and core) extracts were determined in the range of 70 to 95degreesC for 0 to 600 s. The capillary tube method was used to obtain quasi-isothermal conditions. The kinetics of both enzymes showed a biphasic first-order model, while at 70degreesC, LOX in asparagus showed a monophasic first-order behavior. LOX activity was not detected for carrots. Kinetic parameters, k and Ea, were determined for heat-labile and heat-resistant isoenzyme fractions. Additionally, initial and residual activities for both enzymes within tissue sections showed a different distribution and beat stability.