Phenolic Levels and Polyphenol Oxidase Activities of Eggplants (Solanum spp.) During Ripening

Abstract

Phenolic levels and polyphenol oxidase (PPO) activities were determined in various eggplants: Solanum melongena L.
(round and oval varieties), Solanum aethiopicum L. and Solanum gilo L. (big and small varieties) during ripening. There were
variations in the phenolic levels and polyphenol oxidase (PPO) activities in the eggplants during ripening; the pattern of variations was
based on the type of variety. The phenolic levels determined by the Folin-Ciocaultau method increased in all the eggplants in their
overripe stage expect in S.gilo (big variety) which showed a decrease. The activities of polyphenol oxidase (PPO) in the eggplants
were determined using catechol and pyrogallol as substrates. PPO activities with catechol as substrate were higher than that of
pyrogallol. Catechol was observed to be the preferred substrate for the enzyme in all the eggplants. PPO activities, using catechol as
substrate decreased in the overripe stage of all the eggplants except in S.melongena (oval variety) that showed an increase; while the
PPO activities using pyrogallol as substrate increased in overripe stage of all the eggplants except in S.melongena (round variety).
Phenolic compounds are major antioxidants in human diet, therefore the increase observed in their levels in the overripe stage of the
eggplants showed that nutritional benefit can be derived from their consumption. Futhermore the inverse relationship between
phenolic levels and PPO activities in these eggplants except in S.melongena (oval variety) suggests that enzymatic browning decreases
with ripening in these fruits.