Effect of antioxidants and pH on browning and firmness of minimally processed eggplant

Abstract

Minimal processing of eggplant (Solanum melongena L.) generates loss of firmness and polyphenol oxidase catalyzes the oxidation of phenolic compounds producing enzymatic browning. The aim of this study was to evaluate the effect of 1% ascorbic acid and 2% calcium ascorbate in aqueous solution at natural pH of the antioxidant (pH 2.6 and 7.8, respectively), or adjusted to pH 5 with generally recognized as safe substances, mantaining the quality of minimally processed eggplant stored at 5 °C for 6 d. Water was used as a control. The color, firmness, polyphenol oxidase activity, and visual quality was evaluated in the freshly cut fruit at 3 and 6 d of storage. No effect of the treatments on firmness or polyphenol oxidase activity was observed. At 3 d of storage, a correlation was observed between polyphenol oxidase activity and the visual evaluation of the cut product. Samples treated with 2% calcium ascorbate and the rest of the treatments at pH 5 had a lower browning index than those treated with 1% ascorbic acid and the control. At the end of the storage period, the visual quality of the eggplant samples treated with 1% ascorbic acid at pH 5 was evaluated above the marketing limit, whereas those treated with 1% ascorbic acid at pH 2.6 had the lowest quality indicators. An adjustment to pH 5 helps to preserve the luminosity and visual quality of the eggplant, however firmness was not affected by calcium ascorbate or the pH of the medium.

Keywords

• fresh-cut eggplant; oxidative damage; ready-to-eat; reducing agents; texture