103 

 Percent inhibition was determined as described above. For apple PPO, the 

 reaction was carried out at 30°C in 0.1 M sodium phosphate buffer (pH 6.0). 



Effect of Ko.iic Acid on the Hvdroxvlation Capability of PPO , ? 



A 100 III kojic acid solution (0.35 - 5.63 mM) in 0.05 M sodium 

 phosphate buffer (pH 6.5) with 60 [il mushroom PPO (0.5 mg/mL) in water at 

 ambient temperature for 15 min, 840 fil of 1 mM L-tyrosine in the same 

 buffer was added. The reaction was monitored at 475 nm (25°C) for 90 min. 

 For control sample, kojic acid was replaced with buffer. 



Effect of Ko.iic Acid on „ Untake bv PPO Reaction 



The effect of kojic acid on the inhibition of PPO was also conducted 

 using a polarographic method. A 0.1 mL aliquot of apple PPO was added to 

 0.1 mL kojic acid solution (0.28, 0.56, or 1.06 mM) in 0.1 M sodium 

 phosphate buffer (pH 6.0) into the sample chamber of a biological oxygen 

 monitor (YSI model 53, Yellow Springs Instrument Co., Yellow Springs, OH). 

 Following incubation at ambient temperature for 30 min, 2.9 mL of 0.1 M 4- 

 methyl catechol or chlorogenic acid in 0.1 M sodium phosphate buffer (pH 

 6.0) was added. The reaction was allowed to proceed at ambient 

 temperature for 10 min and the consumption rate of O2 was monitored using 

 a Brinkmann Servogor 210 recorder at a chart speed of 1 cm/min. The rate 

 of O2 consumption was determined as the initial slope of the curve; the 

 percent change in O2 was measured against time. For the control sample, 

 phosphate buffer was used in place of kojic acid. Background O2 



.1' 



