189 

 week of storage (Figure 44b). The pH rose from 5.4 to 8.0 for those 

 treated-PPO at 33° and 38°C, but only to 7.2 for that heated at 43°C. 



The profiles of the restorative ability of high pressure C02-treated 

 lobster, brown shrimp, and potato PPOs during a 6-week frozen storage are 

 shown in Figures 45, 46, and 47. After 6 weeks storage, the pH of high 

 pressure COg-treated lobster PPO returned to 9.1 from 5.3, whereas there 

 was no restoration of enzyme activity (Figure 45). Similarly, the pH of 

 brown shrimp PPO rose from 4.5 to 6.50 and there was also no restoration 

 of enzyme activity (Figure 46). For potato PPO, the pH change followed 

 the trend similar to those observed for the previous two PPOs, climbing 

 from 4.08 to 6.07. It was noted that 28% of the original activity 

 (AA^^g^ymin = 0.151 vs. 0.540) was restored for the C02-treated PPO during 

 the first two weeks of storage (Figure 47). After this period, the PPO, 

 however, gradually lost its activity as the storage time increased. This 

 result was similar to the previous observation for PPO subjected to 

 atmospheric (1 atm) CO^ at 33°C. The treated sample restored 15% of its 

 original enzyme activity during the first week of storage (Figure 44b). 



Conclusion 



Lobster PPO exposed to CO^ (1 atm) at 33°, 38°, and 43°C showed a 

 decline in enzyme activity with time. Inactivation kinetics study 

 revealed that lobster PPO was more labile to the combined treatment of CO2 

 and heat than to heat alone. The activities of lobster, brown shrimp, and 

 potato PPOs followed trends similar to that of atmospheric CO2 when these 

 enzymes were subjected to the high pressure (58 atm) COg treatment at 43°C. 

 Results indicate PPOs were more susceptible to high pressure COg than 



