104 

 consumption for kojic acid, substrate, and a mixture of the two was also 

 carried out. 



A similar study was conducted using lobster PPO; in which 10 mM DL- 

 DOPA or catechol in 0.05 M sodium phosphate buffer (pH 6.5) was used as 

 the substrate. Percent inhibition (I) on the rate of 0^ consumption was 

 defined as [(U -U*)/U] x 100, where U and U* were the rate of 0^ 

 consumption in the absence or presence of kojic acid. 



Effect of Ko.iic Acid on Reduction of Cu^"^ 



The method of Andrawis and Kahn (1990) with slight modification was 

 followed. Ten minutes after incubating at ambient temperature, a mixture 

 containing 1 mL kojic acid in 0.05 M sodium phosphate buffer (pH 7.0) and 

 0.5 mL 0.4 mM cupric sulfate (Fisher) in the same buffer was added to a 

 0.5 mL aliquot of 4 mM aqueous bathocuproine disulfonic acid. The final 

 concentration of kojic acid in the mixture was between 0.02 to 1.40 mM. 

 After the mixture was incubated at ambient temperature for another 20 min, 

 the absorbance at 483 nm was determined using a DU-40 spectrophotometer 

 (Beckman). For the control sample, 1 mL phosphate buffer was substituted 

 for kojic acid. 



Effect of Kojic Acid on Quinone Products 



A reaction mixture containing 1.2 mL 10 mM DL-DOPA and 0.8 mL 

 mushroom PPO (0.125 mg/mL) in 0.05 M sodium phosphate buffer (pH 6.5) was 

 incubated at ambient temperature for 30 min. Following red color 

 development due to dopaquinone formation, the mixture was scanned from 220 

 to 700 nm using a spectrophotometer. The effect of kojic acid on 



