The Influence of Ultrasound and Cultivar Selection on the Biocompounds and Physicochemical Characteristics of Dried Blueberry (Vaccinium corymbosum L.) Snacks.

The aim of the study was to characterize physical and chemical composition of four highbush blueberry cultivars ("Bluecrop," "Late Blue," "Chandler," and "Elliot"). The assessment of ultrasound influence at the osmotic dehydration step and during hybrid drying on mass transfer and the nutritional quality of all cultivars was also done. The experiment consisted of two stages: (1) initial: optimization of osmotic dehydration procedure, (2) the main experiment including all stages of dried blueberry production (pretreatment, osmotic dehydration chosen in the initial stage, and drying). In both parts, the effect of US and cultivar were considered as factors influencing the most important quality indices. The osmotic dehydration, in the mixture (1:1) of sucrose solution and apple juice concentrate (65°Bx) at a fruit to syrup ratio 1:4, was carried out in water bath fitted with ultrasonic transducers (25 kHz, 27.8 W/L) at a temperature of 40°C for 150 min. After pretreatment osmo-dehydrated fruits were subjected to drying in hybrid (microwave-ultrasound-convective) drum dryer. Regardless of the cultivar US had positive influence on mass transfer (up to 22% for intact and 12% for mechanically scratched) at the osmotic dehydration stage. Unfavorably, its action tend to decrease phenolic compounds content. The final effect, however, was strongly influenced by the choice of cultivar. With regard to ultrasound applied at the drying step, no explicit effect, either on the drying process efficiency or on final product quality, was identified. In the same processing conditions "Elliot" turned out to be the most promising to produce ready-to-eat fruit snacks in terms of the final product stability and bioactives content. PRACTICAL APPLICATION: Hybrid drying was proposed as a novel approach in blueberry drying. Ultrasound application as a part of abovementioned drying technique is considered an efficient way of shortening drying time due to mass transfer intensification and the interaction with dehydrated tissue. However, no experiments studying the impact of ultrasound on various cultivars within one species were carried out. This study contributes to the understanding that appropriate cultivar selection in the production of ready-to-eat dried blueberry fruit is just as important as process parameters in obtaining an attractive product with a high level of natural bioactive compounds.