Solar drying of flame seedless (Vitis vinifera l.) grape after different pretreatments: characterization of raisin’s physicochemical and functional properties

Five different pretreatment strategies for the drying Flame seedless raisins were used: ultrasound, freezing, dipping in 0.05% NaOH solution, blanching, and enzymatic pretreatment. Results showed that the drying period for dipping pretreated grapes was reduced to less than half compared to Control grapes. The ultrasound pretreatment preserved the total phenolic content better; however, it affected the total flavonoid content. The enzymatic pretreatment was the one that least affected the total flavonoid content. In the radical-scavenging antioxidant capacity assay, slight differences were observed between the pretreatments. The highest mean value was observed by Oxygen Radical Absorbance Capacity in the case of blanching pretreatment. The α-glucosidase inhibitor of raisins was also investigated, obtaining a low inhibition compared to acarbose. The presented results give scientific insight and a basis for the use of pretreatments combined with solar drying of Flame grapes. On an industrial scale, it has the potential to produce good quality raisins.