Purification and kinetic characterization of polyphenol oxidase from Barbados cherry (Malpighia glabra L.)

Polyphenol oxidase (PPO) of Barbados cherry was extracted and purified through ammonium sulfate precipitation, gel filtration, and affinity chromatography. The purification factor for PPO was 60% with 8.3% yield. The enzyme was characterized for thermal stability, pH and kinetic parameters. The molecular mass of PPO was approximately the sum of 52 and 38 kDa estimated by SDS–PAGE. The purity was checked by native PAGE, showing a single prominent band. The optimum pH was 7.2. The enzyme had a temperature optimum at 40 °C and was relatively stable at 60 °C, with 55% loss of activity. Sodium diethyl dithiocarbamate (SDDC), l-cysteine and ascorbate significantly inhibited PPO activity. 4-Methyl catechol and catechol were found to be efficient diphenolic substrates for cherry PPO, considering the _Vmax/_Km$V_{\text{max}}/K_{\mathrm{m}}$ ratio. The data obtained in this study may help to understand cherry fruit browning.