Inhibition of Mushroom Polyphenoloxidase by Ascorbic Acid Derivatives

Ascorbic acid (AA), dehydroascorbic acid (dehydroAA), isoascorbic acid (isoAA), ascorbic acid‐2‐phosphate (AA‐2‐ PO 4 ), and ascorbic acid‐2‐sulfate (AA‐2‐SO 4 ) were tested as inhibitors of mushroom polyphenoloxidase (PPO). Kinetic analysis indicated that AA and isoAA were more effective than dehydroAA. The half times (t 1/2 ) that decreased 50% of PPO activity for AA, isoAA and dehydroAA were 2.5, 3.1, and 1.9 hr, respectively, and the concentrations that inhibited half of PPO activity were as follows: ascorbic acid, 0.04 mM, isoAA, 0.25 mM; and dehydroAA, 7.5 mM. Electron spin resonance studies demonstrated that the Cu 2+ of PPO was reduced to Cu + by AA. AA‐2‐PO 4 and AA‐2‐SO 4 were not inhibitors for PPO. However, the digestion of AA‐2‐PO 4 with acid phosphatase yielded AA to inhibit PPO activity. AA‐2‐SO 4 was found to be a poor substrate for sulfatase.