131 

 563 /iM) of kojic acid (Figure 29). Kojic acid at higher concentrations 

 was shown to exert a profound inhibitory effect on the oxidation of L-DOPA 

 by PPO. Thus, kojic acid did not behave as ascorbate, hydroquinone, H^^j 

 and NH^OH that were reported to be capable of reducing the lag period of 

 hydroxylation of monohydroxyphenol when added at small concentrations 

 (Kahn, 1983; Kahn and Andrawis, 1986; Sato, 1969; Vaughan and Butt, 1970), 



Effect of Koiic Acid on „ Uptake bv PPO Reaction 



Consumption of oxygen did not take place with kojic acid, the 

 substrates (4-methylcatechol and chlorogenic acid for apple PPO, and DL- 

 DOPA and catechol for lobster PPO), or the kojic acid-substrate mixtures. 

 When PPO was added to the mixture containing substrate and buffer, 0^ 

 consumption occurred immediately. Although 0^ uptake by the PPO-substrate 

 mixture still took place when kojic acid was added, the percentage of 0^ 

 consumption in these mixtures decreased with increasing concentrations of 

 kojic acid (Table 6). For example, 0^ consumption for the oxidation of DL- 

 DOPA by lobster PPO in the presence of 0.56 and 1.06 mM kojic acid was 

 inhibited by 60.3 and 80.3%, respectively. 



Effect of Kojic Acid on Reduction of Cu^"^ 



Bathocuproine disulfonic acid reacts with Cu* to form a red color 

 complex having an optimal absorption at 483 nm (Blair and Diehl, 1961). 

 Thus the reducing ability of kojic acid can be determined from the 

 measurement of the absorbance at 483 nm in a model reaction mixture. The 

 absorbance of the reaction mixture increases with increasing 

 concentrations of kojic acid and then reaches a plateau when kojic acid 



