y^rT'^'"''' ».,^-' ■ . - -J --^ .-■ '^ ', ■■,;^~ 



198 

 inhibition for mushroom PPO when DOPA and L-tyrosine were used, 

 respectively. Significant inhibitory effects with different types of 

 inhibition mechanisms were observed with the various PPO activities when 

 DOPA was used as substrate. In addition to mechanisms described 

 previously, kojic acid was shown to inhibit melanosis by interfering with 

 the uptake of oxygen required for enzymatic browning. This compound was 

 capable of reducing o-quinones to o-diphenols; this result suggests that 

 kojic acid could be potentially used as an inhibitor in the prevention of 

 melanosis in plant and seafood products. 



When exposed to CO^ (1 atm) at 33°, 38°, or 43°C, lobster PPO showed 

 a decline in enzyme activity with heating time. When these enzymes were 

 subjected to high pressure (58 atm) CO^ at 43°C, lobster, brown shrimp, and 

 potato PPOs followed trends similar to that of atmospheric CO^. 

 Inactivation kinetics revealed lobster PPO was more labile to CO^ and heat 

 than heat alone. Studies showed PPOs were more susceptible to high 

 pressure CO^ than atmospheric CO^; potato PPO was more resistant than 

 lobster and shrimp PPO to the high pressure CO^. Studies employing 

 polyacryl amide gel electrophoresis showed there were no differences in the 

 protein patterns and isoelectric profiles between the nontreated and CO^ 

 (1 atm)-treated PPO. Differences in secondary structures, protein 

 patterns, and isoelectric profiles however were observed between the high 

 pressure (58 atm)-treated and untreated PPO. Results from the studies 

 suggest that low temperature (< 4°C) storage of foodstuffs that have 

 previously been treated with CO^ could possibly be used as a processing aid 

 to enhance the inactivation of PPO and thus prevent enzymatic browning. 



