.|W.--' - -T ._,^ - - ■< j^v^..;.. 



186 

 noticeable alterations in the composition of a-helix and random coil. In 

 contrast, only minor alteration in secondary structures was observed in 

 high pressure CO^-treated potato PPO (Table 11). These results thus 

 verified the previous finding that potato PPO was more resistant to high 

 pressure CO^ than lobster and brown shrimp PPO (Figures 34, 35, and 36), 

 possibly due to its less responsiveness at altering the secondary 

 structure. The pH change of the system and the possible bubbling effect 

 due to CO^, again were not completely responsible for the loss of PPO 

 activity. This was in agreement with previous findings of Miller et al . 

 (1981) who proposed that the pressure-induced effect from SC-CO2 treatment 

 could cause changes in protein backbone structure and subunit dissociation 

 and thus inactivated the enzyme. 



Restorative Ability nf m. -treated PPO Activity 



Changes in PPO activity and pH after CO^ (1 atm) treatment and during 

 frozen-storage are given in Figures 44a, 44b, 44c, and 44d. Non-CO - 

 treated controls gradually lost PPO activity as time proceeded. Nearly 

 50% of the original activity {LI\^,,Jmin = 0.059) was lost after storage 

 over 5 weeks (Fig. 45a). For CO^ (1 atm)-treated-PPO, only PPO heated at 

 33°C was restored by 10% of its original enzyme activity (AA,„ /min = 



* 475nnr 



0.006) during the first week (Fig. 44b). After one week storage, the PPO 

 activity decreased as storage time increased. CO^ (1 atm)-treated PPOs 

 heated at both 38° and 43°C showed no restoration in activities (Figures 

 44c and 44d). Unlike the pH change in non-CO^-treated PPO which showed a 

 slight decrease in pH with increased storage time (Figure 44a), those 

 subjected to CO2 (1 atm) treatment showed a rapid increase in pH after one 



- -1 



