摘要：Polyphenol oxidase (PPO) from Melissa officinalis L. subsp. officinalis (lemon balm) was partially purified by ammonium sulphate precipitation and dialysis; and then it was characterised in detail in terms of pH and temperature optima, thermal stability, kinetic parameters, and inhibition properties. Based on experimental results, it was found out that ( i ) the optimum pH and temperature values of PPO were 6.5, 4.0, and 8.5 and 40, 50, and 60°C for catechol, 4-methylcatechol and pyrogallol substrates, respectively; ( ii ) the best substrate was pyrogallol due to the highest V max/ Km value, followed by catechol and 4-methylcatechol; ( iii ) enzyme activity decreased due to heat denaturation of the enzyme with increasing temperature and inactivation time for all substrates; ( vi ) gallic acid and l-glutamic acid did not inhibit PPO; and ( v ) the most effective inhibitor was glutathione. Furthermore, the phenolic and protein contents of lemon balm extract were also determined according to the Folin-Ciocalteu and Bradford methods, respectively.
