107 



Results and Discussion 



Effect of Ko.iic Acid on Mushroom PPO Activity 



Kojic acid showed a concentration-dependent inhibitory effect on 

 mushroom tyrosinase oxidation of DL-DOPA (Figure 22). Addition of kojic 

 acid (20 /xg/mL) to the assay system containing DL-DOPA and 

 L-tyrosine inhibited tyrosinase by 72 and 64%, respectively (Figure 23). 

 This inhibitory effect was elevated to 90% when kojic acid at 80 /xg/mL was 

 added. Saruno et al . (1979) reported only 20 to 30% mushroom PPO 

 inhibition when kojic acid at 20 jug/mL was used. The use of different 

 enzyme preparations in these two studies could have affected the 

 inhibitory effectiveness of kojic acid. 



Effect of KoJic Acid on Potato PPO Activity 



Potato PPO was not as effectively inhibited by kojic acid as 

 mushroom tyrosinase especially when catechol was used as substrate (Figure 

 24). Approximately 95% of mushroom tyrosinase activity was suppressed 

 when kojic acid at 200 Mg/mL was used (Figure 23). However, only 55 and 

 25% inhibition of potato PPO was achieved for chlorogenic acid and 

 catechol, respectively, under the same conditions. As kojic acid 

 concentration was increased to 800 /ig/mL, the inhibition of potato PPO on 

 the oxidation of chlorogenic acid approached 90%. However, the inhibition 

 was only 53% for the oxidation of catechol. Abukharma and Woolhouse 

 (1966) demonstrated that 0.1 mM potassium cyanide or sodium azide and 1 mM 

 3,4-dichlorophenyl serine gave about 60% inhibition on potato PPO when 

 chlorogenic acid was used as substrate. 



