INTRODUCTION 



Undesirable enzymatic browning causing the discoloration or 

 formation of black spots (melanosis) by polyphenol oxidase (E.C. 

 1.14.18.1; PPO) on the surface of many vegetable, fruit, and seafood 

 (crustacean) products has been of great concern to food scientists. For 

 food processors, the formation of melanin pigments not only imparts the ,^v 

 problems in sensory attributes and, hence, the marketability of the ^^ 

 product, but often lower its nutritive value as well (Synge, 1975). 



Kinetic properties have been studied for PPO from various sources of '^ 

 vegetables and fruits (Schwimmer, 1981) and more recently from crustaceans .-, | 

 (Ferrer et al . , 1989a; Rolle et al . , 1991; Simpson et al . , 1987, 1988a). 

 However, little comparative biochemical information exists between PPO .:,^ 

 from plants and crustaceans. A preliminary study conducted in this | 

 laboratory revealed that Western Australian lobster {Panulirus cygnus) was 

 far less susceptible to melanosis during storage at refrigeration 

 temperature than Florida spiny lobster {Panulirus argus) maintained under 



the same conditions. It is speculated that the susceptibility to 



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melanosis could be attributed to the difference in PPO activity between 



these two lobster species. Thus, the first objective of this study was to 

 characterize and determine the kinetic properties of PPO enzymes from 

 these two lobsters as well as from other crustacean and plant sources. 



Many chemical and physical methods have been studied for their 

 effectiveness on the inhibition of enzymatic browning. Browning may be 



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