Use In Vivo of Natural Anti-Browning Agents Against Polyphenol Oxidase Activity in Minimally Processed Eggplant

Plant polyhenol oxidase (PPO, EC 1.14.18.1) is responsible along with other oxidases for the enzymatic browning reaction occurring during handling, storage and processing of vegetables and fruits. This enzyme catalyzes the hydroxylation of monophenols to o-diphenols (cresolasic activity) and the oxidation of o-diphenols to the corresponding o-quinones (catecolasic activity) which represent the main reaction product. The o-quinones can react with other substances, phenolic or otherwise, copolymerizing, thus producing pigments responsible for the undesirable browning which decreases the quality of fruit. This work aimed at assessing the efficacy in vivo of some natural anti-browning agents in minimally processed eggplant. The berries were collected, washed, diced, submitted to dipping with inhibitors (ascorbic, benzoic, citric, ferulic and glutamic acid) at three different concentrations (0.2, 0.5 and 1%) and packed in ordinary atmosphere bags (PET), covered by a double barrier film and refrigerated for 7 days (4.0 ± 0.5 °C, 95% RH). The enzymatic activity was inhibited by addition of each anti-browning agents tested. In detail, at the end of the storage period the greater reduction in PPO activity was observed at the highest concentrations (0.5 and 1%) of the inhibitors in the following order: ferulic acid (-43%), glutamic acid (-32%), citric acid (-27%), ascorbic acid (-21%) and benzoic acid (-15%). These positive effects were also translated in terms of browning index. Therefore, the anti-browning treatments studied extended the shelf-life of minimally processed eggplant, thus suggesting an industrial application, e.g. the addition of one or more of these inhibitors into vegetable packages.