Z^'T/'^'- '' 



150 

 treatment parameters were equilibrated to the desired conditions, PPO (8 

 tnL) was sampled after the vessel was removed from the water bath. Each 

 time after sampling, the vessel was replaced into the bath. Sampling was 

 done every minute during the first 5 min and then e^>ery 5 min thereafter. 

 Following equilibration to ambient temperature, PPO activity was 

 determined as previously described. The activity for temperature control 

 treatment was also determined. Percentage of relative activity was 

 determined as (E/EJ x 100, where E, and E^ were the PPO activities at 

 time t and the original activity without heat and CO^, respectively. The 

 pH change resulting from CO, treatment during the course of this study was 

 monitored using a pH meter. >. • 



Kinetics o f PPQ Inart.i^/atinn *• 



The inactivation reaction constant (k) and the activation energy (EJ 

 of PPO in the presence or absence of CO, (1 atm) were determined according 

 to the Arrhenius equation by measuring the initial rate at different 

 temperatures and plotting the logarithmic value of V^^^ versus 1/T (Segel, 

 1976). The D value (decimal reduction value) defined as the time required 

 to inactivate 90% of the original enzyme activity at a constant 

 temperature was determined from the negative reciprocal of the slope from 

 a plot of logarithmic value of enzyme activity versus time (Richardson and 

 Hyslop, 1985). The z value which is the number degrees required for the 

 thermal inactivation curve to traverse one logarithmic cycle was 

 determined by plotting the logarithmic value of (D./D^) versus (T^-T ), 

 where D, and D^ were the D values at temperature T, and Tj (fahrenheit, °F), ' 

 respectively (Richardson and Hyslop, 1985). 



