The effect of pH on the activity, thermokinetics and inhibition of polyphenol oxidase from peach

Abstract

This study focused on the effect of pH on the activity, thermokinetics and inhibition of polyphenol oxidase (PPO) from honeydew peach pulp with (+)-catechin as the substrate. The optimum pH for the PPO activity was around 6.5–7.0, and the optimum temperature was pH dependent and it was 40 °C at pH 6.8 while 30 °C at pH 4.0. The enzyme was stable in the pH range of 6.0–8.0 during the storage at 4 °C. However, the thermokinetics parameters (D, z, k, Ea) of PPO suggested that the enzyme was much more stable at pH 6.8 than at pH 6.0 and pH8.0 during the thermal treatments. Moreover, the results also indicated that the enzyme was more sensitive to the change of temperature at pH 6.8 than at the others pH. The inhibition study indicated that L-cysteine and glutathione were highly effective for the inhibition of the enzyme while NaF inhibited moderately at pH 6.8. However, the inhibition abilities of those inhibitors were pH dependent, and acidic medium could greatly increase the inhibition ability of NaF for peach pulp PPO.