144 



dioxide (CO2) was used as the fluid. CO^ is used in SC fluid because it 

 is nontoxic, nonflammable, inexpensive, and readily available 

 (Hardardottir and Kinsella, 1988). CO^ has a relatively low critical 

 temperature and pressure (Rizvi et al., 1986). Taniguchi et al . (1987) 

 studied the retention of alpha-amylase, glucose oxidase, lipase, and 

 catalase activity by SC-CO2. Although SC-CO2 has been shown to inactivate 

 PPO, information regarding the inhibitory effect and the inactivation 

 kinetics of SC-CO2 on purified PPO has not been elucidated. This study was 

 undertaken to investigate the effect of CO2 (1 or 58 atm) on the 

 inactivation of Florida spiny lobster, brown shrimp, and potato PPO. 



Materials and Methods . > ., , -^ ^ 



Fresh Florida spiny lobster {Panulirus argus) tails were obtained 

 from the Whitney Marine Laboratory and transported in ice to the 

 laboratory and stored at -20°C. Russet potato tuber was purchased from a 

 local supermarket. Non-sulfited fresh brown shrimp {Penaeus aztecus) were 

 obtained from a local seafood store. Lobster cuticle, shrimp 

 cephalothorax (head), and potato peel were frozen in liquid nitrogen and 

 ground into a fine powder using a Waring blender. The ground powder was 

 stored at -20°C until needed. 



Extraction and Purification of Lobster, Shrimp, and Potato PPO 



PPO was extracted and purified following the procedures of Chen et 

 al . (1991a). Ground powder was added to 0.05 M sodium phosphate buffer 

 (pH 7.2) (1:3, w/v) containing 1 M NaCl and 0.2% Brij 35, stirred for 0.5 

 hr at 4°C, and then centrifuged at 8,000g (4°C) for 30 min. The 



