Influence of ozonated water on the structure and on some quality parameters of whole strawberries in modified atmosphere packaging

Strawberry fruits (Fragaria x ananassa Duch. cv. Darselect) were submerged in ozonated water (1.66 ppm) for 5 minutes, packed in air and in modified atmosphere (65% N2O, 25% Ar, 5% O2, 5% CO2) and stored at 4ºC for 20 days. SEM analysis of the surface cells of the fresh product before and after treatment were performed. Titrable acidity, color and texture modifications during storage were assessed. Color evaluation of surface of the fruit showed a rapid increase of red index (a*) and decrease of luminosity values (L*) during storage, in particular for sample pretreated and packed in air. The results of color determinations, performed with image analysis on strawberry sepals, indicated a preservative effect of the ozonated water pretreatment. SEM images of the walls cell close to the fruit surface of untreated and treated samples, showed some irregular shape of cells of pretreated strawberries, compared to those of untreated fruit. The dynamometric results, obtained with texture analyzer, did not show significant differences in the decrease of maximum firmness between samples. However, the energy required to penetrate the surface layer (5 mm close to the surface) of treated and untreated strawberry samples differed significantly, confirming a more pronounced superficial softening in fruits pretreated with ozonated water. Moreover, the sample not ozonated and packed in MA showed, in comparison to control sample (paked in air), a reduction in rate of softening and a preservative effect on color during the early period of storage. Ozonated water pretreatments seem to be not effective in prolonging the shelf-life of strawberries, in particular in terms of maintenance of surface layer firmness.