Purification and characterization of polyphenol oxidase from myrtle berries (Myrtus communis L.)

Myrtle (Myrtus communis L.) belongs to Myrtaceae family in botany and is mostly grown in Mediterranean Basin. Browning reaction because of polyphenol oxidase (PPO) can be observed in the plant that is rich in phenolic substances. This study, it was aimed to determine and purify some biochemical properties, kinetic parameters, the thermal stability of the PPO enzyme of myrtle fruit. In this study, optimum temperature, optimum pH, substrate specificity, the thermal stability of polyphenol oxidase partially purified from white myrtle berries, and the effect of inhibitors on enzyme activity were investigated. Catechol was used as a substrate. The PPO was identified and purified using ammonium sulphate precipitation and ion exchange chromatography. Optimum pH and temperature were found as 6.8 and 30 degrees C respectively for myrtle PPO while Km and Vmax values were calculated as 3.34 mM and 4.1 mL/min. In thermal inactivation studies at 60, 70, and 80 degrees C reaction rate constants (k) were found as 0.0282, 0.526, and 0.1117 /min, thermal half-life times (t(1/2)) were calculated as 24.6, 13.2, and 6.2 min, and decimal reduction time (D-value) was calculated as 81.6, 43.8 and 20.6 min, respectively. The activation energy (Ea) and Z-value were calculated as 67.2 kJ/mol and 33.4 degrees C, respectively. Similar inactivation ratios from 40 to 100% were observed for both inhibitors of ascorbic acid and disulfide at 0.01-10 mM concentration. PPO from myrtle was successfully purified to 5.5 purification fold with 8% recovery, by using DEAE-Sephacel chromatography.

Automated summary

This study investigated the biochemical properties and thermal stability of polyphenol oxidase (PPO) in myrtle fruit. Optimum temperature and pH for myrtle PPO were found to be 30 degrees C and 6.8 respectively. The study also showed that both ascorbic acid and disulfide can inhibit the activity of PPO.