Biopreservation of 'Birgah' Eggplant from Polyphenol Oxidase Activity Assayed In Vitro with Onion (Allium Cepa L.) by-products.

Eggplants are vegetables largely consumed in many recipes as fresh and whole product or, more recently, as minimally processed vegetable (MPV). The main issue in diced eggplant consists in the oxidation due to polyphenol oxidase (PPO, EC 1.14.18.1), an enzyme producing pigments responsible for the undesirable dark color which spoiled the product. The aim of this work was to study fresh or heat-treated (100 °C for 15 min) onion by-products (paste, juice and bagasse) in order to evaluate in vitro the PPO enzyme inhibition capacity in minimally processed eggplant cv. 'Birgah'. The heated onion juice was the most suitable anti-browning extract among all by-products tested, followed by pasteurised paste and fresh juice (54.2, 41.2 and 37.3 % reduction in PPO activity, respectively). Data suggested that the thermal treatment enhances the effects of the extracts probably due to a synergic action between some endogenous active compounds present in onion and Maillard reaction products obtained during heating