Effect of Ultrasound-Ethanol Pretreatment on Drying Kinetics, Rehydration, Quality Parameters, and Functional Groups of BRS Vitória Grape Using Convective Drying

The aim of this study was to investigate the effects of ultrasound pretreatment to improve BRS Vitória grape convective drying. For this purpose, samples without any pretreatment (control) and samples pretreated with ultrasound and water (USW) or ethanol (USEtOH) were analyzed. The effects on drying and rehydration kinetics, quality parameters, total phenolic content, antioxidant capacity, and functional groups were studied through FTIR spectrometry. The results showed that the pretreatment with ultrasound and ethanol reduced the grape’s drying time by approximately 64%. The Weibull model was the best model to describe the kinetics of grape rehydration. USEtOH-pretreated samples exhibited the greatest rehydration ratio at both tested temperatures (25 and 50 °C), especially at the highest one. In terms of quality parameters, soluble solids content and color change were influenced by pretreatments, with USEtOH showing a substantial reduction in grape water activity and significant color change after drying. The content of total phenolics decreased after ultrasound pretreatments but increased during drying, with USEtOH showing better retention of these compounds. Antioxidant capacity was affected by drying, but ultrasound pretreatments mitigated losses. Functional group analysis revealed that pretreatments were able to preserve several groups identified by FTIR. These results highlighted the potential of emerging and non-thermal technologies as pretreatments for drying BRS Vitória grapes, which suggests their use in food industry applications.