Fluidized bed drying of blackberry wastes: Drying kinetics, particle characterization and nutritional value of the obtained granular solids

Abstract

Particulate systems for functional ingredient development were obtained by fluidized bed drying of blackberry wastes. Fluidization behavior, drying characteristics, and physicochemical and functional properties were studied at different air temperatures (50, 60 and 70 °C) and an airflow rate of 6 m/s. Under these conditions, the blackberry waste -a heterogeneous and high-humidity material- could be successfully transformed into granulates under bubbling fluidization regime and without the use of inert material. The Page model was the most suitable to predict the blackberry waste drying behavior. Drying rate increased with temperature and the time to reach a granulate of aw < 0.3 was reduced from 30 min (at 50 °C) to 12 min (at 70 °C), producing particles of lower humidity and size with fair flowability. The optimal operating condition was a 60 °C temperature which allowed to produce a mean-size particle granulate, with fair flowability (Carr index = 15.9 ± 1.4%), and high in dietary fiber content (79.9% ± 0.4%), polyphenol content (1800 ± 34 mg GAE/100 g) and antioxidant capacity (≈1088 ± 57 GAE/100 g by ABTS and 1012 ± 93 by FRAP methods). Additionally, a better balance between the fiber types and high retention of blackberry pigments and color was obtained.