147 

 activity was determined by adding 60 m PRO into a microcuvette containing 

 840 ML 10 mM DL-DOPA in 0.05 M sodium phosphate buffer (pH 6.5). The 

 reaction was monitored at 475 nm (25°C) for 5 min. The activity of N^- 

 treated and non-gas-treated controls heated at 33°, 38°, or 43°C were also 

 determined as previously described. Percentage of relative activity was 

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

 time t and original activity, respectively. Changes in pH resulting from 

 CO2 treatment was monitored using a digital pH meter (E632, Metrohm Ltd., 

 Switzerland) equipped with a microelectrode. 



pH Control Study 



Mixtures containing 1 mL PPO preparation and 3 mL NaHCOg (pH 5.3) 

 were heated for 30 min at 33°, 38°, and 43°C, respectively, in a water 

 bath. The mixture was then instantly removed and emerged into a 0°C ice 

 chest. Following equilibration to ambient temperature, PPO activity was 

 assayed as previously described. 



Effect of high prp^<;rirp rn^ on ppp activity 



The apparatus used for PPO inactivation by high pressure CO^ is shown 

 in Figure 32. CO, was connected to a high-pressure resistant stainless 

 steel vessel (volume = 100 mL) equipped with valves through a metal hose. 

 After the vessel was immersed into a water bath maintained at 43°C, a 

 constant pressure of 850 psi (58 atm) inside the vessel chamber was 

 achieved by adjusting the pressure-regulating valve. For each study, 80 

 mL lobster, brown shrimp, or potato PPO was placed in the vessel. After 



