Effects of calcium citrate and ascorbate as inhibitors of browning and softening in minimally processed ‘Birgah’ eggplants

Eggplant is a very common Sicilian vegetable destined for fresh consumption and/or for the fresh-cut processing industry. Nevertheless, due to minimal processing it becomes susceptible to browning and softening during storage, even under chilling conditions. The browning process is mainly related to polyphenol oxidase (PPO, EC 1.14.18.1) oxidative action, whereas softening is to pectin methylesterase (PME, EC 3.1.1.11) and polygalacturonase (PG, EC 3.2.1.15). The aim of this work was to determine the effect of the application as a dipping treatment of two different Ca salts and heat shock (60°C for 1min), on quality of minimally processed hybrid F1 ‘Birgah’ eggplant (Solanum melongena L.). For this purpose, polyphenol oxidase, pectin methylesterase, polygalacturonase, total phenolics, colour parameters, firmness and total visual quality, were monitored throughout 10d storage at 4±0.5°C under a passive atmosphere (O₂: 20.20%; CO₂: 0.50%). After minimal processing, eggplant cubes were alternatively dipped in Ca salts (ascorbate or citrate) solutions using the same concentration (0.15g⁻¹). A dipping treatment in sterile distilled water without Ca salts at 60°C for 1min was used as the control. The dipping with Ca ascorbate was the best treatment for its great efficacy against degradative enzymatic activities, thus improving consumer overall acceptance. The quality properties of the eggplant cubes was quite unaffected throughout the first 4d of storage, but were acceptable up to day 7. Together with a noticeable inhibition of the three tested enzymes, a significant reduction of browning and softening was obtained in comparison to the control sample collected on the same day, whereas a significant quality loss of the minimally processed vegetable appeared beyond this storage period.