Characterization and changes in polyphenol oxidase from eggplant fruit (Solanum melongena L.) during storage at low temperature

Polyphenoloxidase (PPO) from eggplant fruit was characterized, and its catecholase activity studied during storage of fruit at 0 and 10 °C. The high catecholase activity was observed using 4-methylcatechol as substrate at pH 6 and 30 °C and activation with sodium dodecyl sulphate (SDS) was unnecessary. The soluble PPO fraction was the most thermostable, as well as the most active, form of the enzyme. Fruits stored at 10 °C were undamaged, whereas those kept at 0 and 5 °C experienced chilling injury from days 6 and 8, respectively, as indicated by the decrease of lightness (L0) of pulp tissue. During exposure of fruits at 10 °C, the activities of soluble and insoluble PPO fractions increased, whereas, at 0 °C, PPO activity of both fractions decreased and maintained lower levels when browning of pulp tissue was observed. Soluble PPO activity at 0 °C was directly related to the value for L0.