. 'I 



2 



prevented not only by inactivating the enzyme, but also by eliminating 

 substrate (0^ or polyphenol) necessary for the reaction, or by reacting 

 with the products of the enzyme reaction thus preventing the formation of 

 the quinones necessary for the preceding non-enzymatic steps. Although 

 some chemicals have been shown to inhibit PPO activities, their use in 

 food processing is restricted by many concerns such as toxicity, 

 wholesomeness, effect on taste, flavor, texture, etc. (Vamos-Vigyazo, 

 1981). Kojic acid (5-hydroxy-2-hydroxymethyl-7-pyrone), a fungal 

 metabolite produced by many species of Aspergillus and Penicillium 

 (Kinosita and Shikata, 1964), has been reported for its inhibitory effect 

 on mushroom PPO (Saruno et al., 1979). Kojic acid mixed with ascorbic 

 acid and citric acid constitutes a Japanese commercial product which is 

 used as a tyrosinase inhibitor in foods. Since only limited information 

 was available on the inhibitory activity and mechanism of kojic acid on 

 PPO, the second objective of this study was to investigate the inhibitory 

 activity of this compound on crustacean (Florida spiny lobster, white 

 shrimp, and grass prawn) mushroom, and plant (potato and apple) PPO and to 

 elaborate the mechanisms of inhibition. 



In past years, treatment in an atmosphere modified with carbon '^ 

 dioxide has been used as an application for retarding enzyme activity, to 

 preserve food quality and to extend the shelf -life of food products. 

 Recently, inactivation of peroxidase, PPO, pectinesterase, a-amylase, 

 glucose oxidase, lipase, or catalase by supercritical fluid using COg as 

 the solvent has been reported by many workers (Arreola, 1990; Christianson 

 et al., 1984; Taniguchi et al . , 1987; Zemel , 1989). However, information 

 concerning the inhibitory effect and the inhibition mechanism of COg on 



