Vacuum-belt drying of rabbiteye blueberry (Vaccinium ashei) slurries: influence of drying conditions on physical and quality properties of blueberry powder.

摘要

Continuous vacuum-belt drying was studied as a means to produce high-quality powders from blueberry slurries, with limited degradation of anthocyanins. Drying was performed at three different temperatures (80, 95, 110 degrees C) and the resulting dried material (a _w ~ 0.2) ground into powders. Drying times ranged from 70 min at 80 degrees C to 50 min at 110 degrees C. Maltodextrin (MD) was used as a drying agent at three levels (0.3, 0.45, and 0.6 kg/kg dry blueberry solid). Powders were purple, with no signs of browning, and similar in appearance to those produced by freeze-drying. Increasing MD level and drying temperature decreased the hygroscopicity of the powders. Moisture isotherms showed type 3 behavior and were well-fit with the Guggenheim-Anderson-de Boer equation. Higher levels of MD improved flowability of the powders, with >93 % of the powders with MD flowing from the test fixture after 30 s, compared to only 62.1 % emerging for powders without MD. Powders dried at 80 degrees C were slightly darker (L* = 25.730-28.4) than those produced 110 degrees C (L* = 27.10-28.53), presumably due to less degradation of anthocyanins. Total monomeric anthocyanins (TMA) for MD dried at 80 degrees C (13.1 mg C3G/g) were not different than for freeze-dried blueberries. Higher drying temperatures caused some loss of TMA. Higher levels of MD result in lower TMA by increasing the amount of dry matter in the powders. Vacuum-belt drying at 80 degrees C with 0.3 kg MD/kg dry solids produced non-sticky powders with anthocyanin content similar to freeze-dried powders