The Effect of Hybrid Drying (Convective-Microwave-Ultrasound) on the Bioactive Properties of Osmo-Treated Sour Cherries

The aim of the study was to assess the usefulness of hybrid drying methods (convective-microwave and convective-microwave-ultrasound) for sour cherry fruit preservation compared to convective drying. As the raw material, three sour cherry cultivars varying in quality characteristics (‘Łutówka’, ‘Debreceni Bötermo’, ‘Nefris’) were used. Before drying, fruits were subjected to osmotic treatment. Three different drying methods were examined: 1) convective (C), 2) hybrid with microwaves (C-MV) and 3) hybrid with microwaves and ultrasound (C-MV-US). As the quality indicators of the investigated processes, the changes in chemical composition, including alterations in the main groups of bioactive components, as well as in the antioxidant potential were monitored at each production stage. It was found that, when compared to convective drying, the use of the hybrid techniques allowed the drying time to be reduced from 9 to just 3 hours. Furthermore, employing hybrid drying eliminated the problems associated with the dehydration barrier observed during convective drying of the cultivar ‘Debreceni Bötermo’. Regrettably, although the ultrasound used as the additional source of energy in the hybrid method slightly improved water evaporation, in general no significant effect on the retention of phenolic compounds was found. Irrespectively of the drying method, the effect of the cultivar proved to be crucial to the quality of the final product. Under the same processing conditions, ‘Nefris’ turned out to be the most promising cultivar for producing ready-to-eat fruit snacks of high nutritional value.