Effects of Ultrasound Assistance on Dehydration Processes and Bioactive Component Retention of Osmo-Dried Sour Cherries

Despite having numerous health benefits, dried sour cherries have proven to be more acceptable to consumers when infused with sugar or other sweeteners to enhance their flavor, which, in turn, leads to serious anthocyanin losses. For this reason, a consideration was made for the application of ultrasound to accelerate solid gain and shorten drying time, thus favoring bioactive component retention. To determine the usefulness of ultrasound as a tool for sour cherry osmotic infusion enhancement, the effect of sonication time on dehydration effectiveness, as well as the stability of bioactive components during osmotic treatment and consecutive convective drying, was investigated. Fruits were osmo-dehydrated using a 60% sucrose solution for 120 min (40 degrees C), during which, ultrasound of 25 kHz (0.4 W/cm(2)), was applied for 0, 30, 60, 90, and 120 min, after which, the fruits were convectively dried. In the range of the applied ultrasound energy no significant effect of sonication on mass transfer intensification was observed; moreover, longer acoustic treatment seemed to retard moisture removal during subsequent convective drying, which can be related to the breakdown of the parenchyma cell walls caused by the prolonged ultrasound (US) action. It was concluded that although US assistance could be considered neutral for bioactive component retention, excessive sonication time can lead to some anthocyanin deterioration. According to high-performance liquid chromatography analysis, the particular anthocyanin alterations, both during dehydration and final drying, occurred in a similar way. Sonication time prolongation caused approximately 10% more bioactive compound deterioration, than earlier, shorter trials. Practical Application The aim of the paper was to verify recent literature reports indicating ultrasound (US) application as a feasible method for accelerating fruit dehydration processes. Sour cherries were selected as a model fruit on the basis of their extraordinary nutritional value, which is highly regarded throughout the world. Contrary to expectations, however, US-assisted osmotic dehydration of sour cherries was not as effective as anticipated. With regard to the aspect of US influence on anthocyanin retention, it was proven that although US assistance could be considered neutral for bioactive component retention, excessive sonication time can lead to some anthocyanin deterioration.