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 degreesC. The high catecholase activity was observed using 4-methylcatechol as substrate at pH 6 and 30 degreesC 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 degreesC were undamaged, whereas those kept at 0 and 5 degreesC experienced chilling injury from days 6 and 8, respectively, as indicated by the decrease of lightness (L-0) of pulp tissue. During exposure of fruits at 10 degreesC, the activities of soluble and insoluble PPO fractions increased, whereas, at 0 degreesC, PPO activity of both fractions decreased and maintained lower levels when browning of pulp tissue was observed. Soluble PPO activity at 0 degreesC was directly related to the value for L-0. (C) 2004 Elsevier Ltd. All rights reserved.