Multiple Effects of Maltol and Kojic Acid on Enzymatic Browning

Maltol (3-hydroxy-2-methyl-4H-pyran-4-one) inhibits the rate of oxidation of different o -dihydroxyphenols by tyrosinase when assayed spectrophotometrically but not when assayed polarographically. This finding, as well as spectral data obtained, suggest that maltol does not inhibit tyrosinase activity per se but only gives an apparent inhibition probably due to its ability to conjugate with o -quinones. Kojic acid (5-hydroxy-2 (hydroxymethyl) - 4H-pyran-4-one), a γ-pyrone closely related to maltol, is a very effective inhibitor of tyrosinase as judged by its effect on the rate of pigmented products formation and on the rate of oxygen uptake when different o -dihydroxyphenols are oxidized by the enzyme. In addition to the ability of kojic acid to inhibit the enzyme per se, the data show that kojic acid can change the spectrum of some pigmented products formed in its absence, probably due to the ability of some o-quinones, formed enzymatically, to oxidize kojic acid to a yellow product(s). This possibility is supported by the finding that kojic acid is oxidized to a yellow product(s) by the horseradish peroxidase/H 2 O 2 (HRP/H 2 O 2 ) system as well as by NaIO 4, Ag 2 O and KMnO 4 .