In brief, 500 ll of
50 mM potassium phosphate buffer and 10 mM catechol were
pre-warmed at 25 C for 5 min. Two hundred and fifty microlitres
of the extract of was then added and mixed, and incubation was
continued for further 5 min. Absorbance was measured at
420 nm and activity was calculated by defining 0.01 absorbance
as 1 unit. Heat inactivation of PPO was determined by measuring
remaining enzymatic activity after heat treatment of 2 ml of the
crude extract either in a water bath or in boiling water for the indicated
duration. Inactivation of PPO by microwave was determined
as in above except for microwaving at 500 W (RO-S22, Mitsubishi,
Tokyo, Japan) instead of heating the sample. The samples were
immediately transferred on ice after the treatment.