159 



observed for PPO samples heated at 38° and 43°C after 20 min (Table 8). 

 Thus, the loss in enzyme activity of CO^-treated PPO was not due to the 

 purging effect from the bubbling gas. 



Effect of High Pressure CO . on PPO Activity 



Heating of lobster and brown shrimp PPO at 43°C for 30 min caused 

 some loss of enzyme activity {Figures 34 and 35). Such treatment, 

 however, caused only 5% loss of potato PPO activity (Figure 36). No 

 protein precipitation occurred in treated samples. 



Treatment of these PPO with high pressure (58 atm) CO^ at 43°C, 

 however, caused a dramatic loss of enzyme activity (Figures 34, 35 and 

 36). Lobster, brown shrimp, and potato PPO, after treatment for 1 min, 

 retained only 2 (AA^^^ymin = 0.001 vs. 0.083), 22 (0.010 vs. 0.046), and 

 45% (0.240 vs. 0.540), of the original enzyme activity, respectively. 

 Extended treatment of lobster and brown shrimp PPO for more than one min 

 caused a complete loss of enzyme activity. For these two PPOs, the 

 treatment for 10 and 15 min respectively caused protein precipitation. 

 High pressure COg treatment thus caused PPO denaturation and the loss of 

 lobster and brown shrimp enzyme activity. The results also showed that 

 brown shrimp PPO was slightly more resistant than lobster PPO to high 

 pressure CO2 treatment at 43°C, and potato PPO was the most resistant of 

 the three. Potato PPO eventually lost 91% of its original activity after 

 treatment for 30 min (Figure 36). Florida spiny lobster PPO was more 

 susceptible to high pressure CO2 than atmospheric CO2; treatment of this 

 PPO for 20 min with atmospheric CO^ (1 atm) at 43°C did not cause complete 

 loss of the enzyme activity (Figure 33c). In comparison with the studies 



