39 

 labile; a short exposure of the enzyme to temperatures at /O-WC is 

 sufficient to cause partial or total irreversible denaturation. Crude PPO 

 isolated from deep sea crab was shown to be inactivated at 70°C (Marshall 

 et al., 1984). Similarly, apple PPO (Walker, 1964) and grape PPO (Vamos- 

 Vigyazo, 1981) were found to be markedly inactivated at temperatures above 

 70°C. For banana PPO, an exposure to 80°C for 15 min was required to 

 inactivate enzymes completely (Galeazzi and Sgarbieri, 1978). Out of 22 

 cultivars of different stone fruits, peach PPO was found the least 

 thermostable and the greater heat stable enzyme from plum and cherry was 

 accompanied by higher activity when compared to peach PPO (Dang and 

 Yankov, 1970). 



Vamos-Vigyazo (1981) pointed out that the thermotolerance of PPO is 

 dependent on the source of enzyme. In addition, different molecular forms 

 of PPO from the same source may behave differently in thermostabilities. 



Activatio n Energy (F ^ ) of Lobster PPO , /" i 



The activation energies, E^, for Florida and Australian lobster PPO 

 were 6.9 and 7.5 Kcal/mole, respectively. These E, values were similar to >• 

 TAPOl (7.8 Kcal/mole) from Florida spiny lobster PPO (Ferrer et al . , 

 1989a), and comparable to shrimp PPO (E3 = 5.2 Kcal/mole) (Bailey et al . , 

 1954), but somewhat different from those of the PPO prepared from white 

 shrimp (E, = 13.9 Kcal/mole; Simpson et al . , 1987), pink shrimp (E^ = 11.5 

 Kcal/mole; Simpson et al . , 1988a), and grass prawn (E^ = 13.3 Kcal/mole; 

 Rolle et al., 1991). The E3 of banana PPO was found to be 4.4 Kcal/mole 

 when catechol was used as substrate (Palmer, 1963). 



