Pre-Treatments Involving Aqueous Ozone and UV-C Light Can Be Used in Raisin Production to Decrease the Incidence of Aspergillus carbonarius and Promote Drying

In order to reduce fungal contamination in grapes and increase the dehydration rate for producing raisins, the development of alternative technologies that do not compromise product safety and quality is required. This study examined the impact of innovative pre-drying methods using aqueous ozone (10 min-4.1 mg O₃ L^-1) and UV-C light (30.3 kJ m^-2 UV-C) on the incidence of <i>Aspergillus carbonarius</i>, as well as on air-drying kinetics and ultrastructure of epicuticular waxes in Sultanina grapes, when applied either individually or sequentially. The effect of the pre-treatments on the colour of the dehydrated grapes was also assessed. Grapes pre-treated with 30.3 kJ m^-2 UV-C and 10 min-4.1 mg O₃ L^-1 + 30.3 kJ m^-2 UV-C showed a lower incidence of <i>A. carbonarius</i> in storage at 20 ± 1 °C than those exposed to aqueous ozone (30 and 8% lower infection compared to the non-pretreated fruit at 15-day storage, respectively). Although the combined pre-treatment did not significantly improve the fungus inhibition with respect to the individual UV-C application, it allowed a higher dehydration rate during the drying process at 60 ± 1 °C. The drying time was reduced by ~31% compared to non-pretreated fruit, a result slightly lower than that achieved with the traditional chemical pre-treatment of ethyl oleate-K₂CO₃ (~39%). This enhancement in drying rate was partly attributed to marked alterations in the grape's epicuticular wax layer. UV-C and the combined pre-treatment helped in reducing the browning of raisins. Therefore, the combined application of ozone and UV-C light could be an environmentally friendly alternative for both improving the microbiological quality of grapes and accelerating the drying process.