Influence of Different Drying Techniques on the Drying Kinetics, Total Bioactive Compounds, Anthocyanin Profile, Color, and Microstructural Properties of Blueberry Fruit

In this study, four different drying techniques, namely, hot air drying (HAD), vacuum drying (VD), ultrasound-assisted vacuum drying (UAVD), and freeze-drying (FD), were applied to blueberries. The drying times of blueberries were 1290, 1050, and 990 min for HAD, VD, and UAVD, respectively, meaning that ultrasound application significantly reduced the drying time. All dried samples except those with FD showed lower total phenolic content and antioxidant capacity than fresh samples. Samples dried with FD had a higher content of bioactive compounds than those dried with other techniques followed by UAVD. The malvidin-3-O-galactoside was the most abundant anthocyanin in the blueberries and was significantly reduced after drying with HAD, VD, and UAVD. Scanning electron microscopy (SEM) analysis of the blueberries dried with FD and UAVD exhibited less shrinkage and cell disruption and more structure. The color parameters L*, a*, and b* values of the samples were significantly affected by the drying technique (p < 0.05). According to the findings of this study, ultrasound-assisted drying technology could be employed to shorten the drying time and improve bioactive retention in blueberry fruits.