KAHN, V., Department of Food Science, Agricultural Research Organization the Volcani Center, POB 6, Bet Dagan, Israel
ZAKIN, V., Department of Food Science, Agricultural Research Organization the Volcani Center, POB 6, Bet Dagan, Israel

Kojic acid [5‐hydroxy‐2‐(hydroxymethyl)‐4‐pyrone] inhibited effectively the rate of pigment formation during the oxidation of pyrogallol, 2, 3,4‐THAP (2, 3,4‐trihydroxyacetophenone) and 2, 4,5‐THBP (2, 4,5‐trihydroxybutyrophenone) by tyrosinase. On the other hand, kojic acid had a synergistic effect on the rate of methyl gallate and n‐propyl gallate oxidation to pigmented product(s) (λmax= 360 nm and λmax= 380 nm, respectively). However, kojic acid inhibited effectively the rate of oxygen uptake when each of the above trihydroxyphenols was oxidized by tyrosinase. These results suggest that kojic acid inhibits tyrosinase per se (probably due to its ability to bind copper at the active site of the enzyme) and that it exerts only an apparent stimulatory effect during the formation of pigmented product (s) from methyl gallate and n‐propyl gallate. Proof for the latter was obtained by a time‐course experiment of kojic acid addition and examination of the spectra of pigmented product(s) formed in the absence versus presence of kojic acid, which suggested that the o‐quinone of n‐propyl gallate and the o‐quinone of methyl gallate can each convert kojic acid to a yellow product(s) absorbing at the 360–380 nm region. Copyright © 1994, Wiley Blackwell. All rights reserved