Enzymatic and chemical oxidation of trihydroxylated phenols

Gallic acid, pyrogallol and gallic acid methyl ester were kinetically characterised as substrates of polyphenoloxidase (PPO) and peroxidase (POD) and their pro- and anti-oxidant capacities were studied. The data obtained are correlated with the chemical shifts of the carbons supporting the vicinal hydroxyls obtained by 13C NMR. Pyrogallol showed the highest catalytic constant for both PPO and POD, reflecting its low δ2 value. This also implies that both enzymes have a high Michaelis constant for pyrogallol. llol also showed higher pro- and anti-oxidant activity (generating H2O2) than did gallic acid and gallic acid methyl esters. However, gallic acid inhibited the formation of H2O2, due to the peroxidation reaction with its carboxylic group, which generated O2.