Effect of antioxidants and pH on the quality and polyphenol oxidase activity of minimally processed eggplant (Solanum melongena L.)

Abstract

Minimally processed vegetables make cooking faster and facilitate their consumption, while the addition of antioxidants extends their shelf life. Antioxidants, such as ascorbic acid (AA) and calcium ascorbate (AsCa), can control enzymatic browning and loss of firmness of fresh-cut eggplants (Solanum melongena L.) by pH-dependent control. The objective of this study was to evaluate the effect of AA and AsCa on color, firmness, activity of the enzyme polyphenol oxidase (PFO) and visual quality of minimally processed eggplant stored for 6 d at 5 °C. The experimental design was a multilevel factorial with 17 treatments and three replications, where n=12 cubes of eggplant were used per replication. The cubes were submerged in aqueous solutions of 1 % AA (w:v), 1 % AsCa (w:v) and 2 % AsCa (w:v) and pH (3 to 4, 4 to 5 and 7 to 8) buffers. Controls for each pH interval were submerged in water or buffer solutions without antioxidants. pH and antioxidants did not affect firmness. After 3 d of storage, acid pH and antioxidants decreased PFO activity, but on day 6 no significant differences were observed. The solutions of AsCa with pH 4 to 5 and 7 to 8 and of AA with pH 7 to 8 effectively controlled enzymatic browning for 6 d of storage. Control of browning and commercial quality of minimally processed eggplant fruits can be optimized if the pH is maintained close to neutral.