

Abstract of Dissertation Presented to the Graduate School : 

 of the University of Florida in Partial Fulfillment of the 

 Requirements for the Degree of Doctor of Philosophy 



CHARACTERIZATION AND COMPARISON OF PLANT AND CRUSTACEAN 

 POLYPHENOL OXIDASES: KINETICS AND INHIBITION BY CHEMICAL METHODS 



By 



JON-SHANG CHEN 



December, 1991 



Chairman: M.R. Marshall ■ ^■i 



Cochair: C.I. Wei ^ 



Major Department: Food Science and Human Nutrition 



The characterization and comparison of polyphenol oxidase (PPO, E.C. 

 1.14.18.1) from crustaceans (lobster and shrimp) and plants were made. 

 PPO from various plant and crustacean sources varied with respect to 

 molecular weight, pH and temperature effects on activity and stability, 

 substrate specificity, and other kinetic parameters. Differences in 

 conformational structure among PPOs from mushroom, potato, lobster, white 

 shrimp, and brown shrimp were investigated using spectropolarimetric and 

 immunological methods. Varied secondary structures were observed among 

 these PPOs, although they were shown to possess similar antigenic 

 determinants. 



Kojic acid [5-hydroxy-2-(hydroxymethyl)-7-pyrone], a fungal 

 metabolite, exhibited competitive and/or mixed types of inhibition on the 

 oxidation of various phenolic substrates (L-tyrosine, DL-^-3,4-di hydroxy 

 phenylalanine, 4-methyl catechol , catechol, and chlorogenic acid) by 

 mushroom, potato, apple, and crustacean (lobster, grass prawn, and white 



xii 



t-K 



f^f^ 



