Dehydration of Red Beet Root (Beta vulgaris) by Hot Air Drying: Process Optimization and Mathematical Modeling

Convective hot air drying was optimized with the objective of maximum color retention of red beet. The process was mathematically modelled as a function of hot air temperature, batch time, and moisture. New semi-theoretical model was tested with experimental data (50 to 120 degrees C) and was found better than 9 other reported models. Estimated effective moisture diffusivity was 3.01x10(-9) to 7.21x10(-7) m(2)/s and it obeyed Arrhenius's equation. Color and rehydration ratio were used to assess the quality of beet powder. An unusual trend of color minima was also observed; which was attributed to the physical phenomena of surface moisture. The final color of beet was temperature dependent and maximum color retention was achieved at lowest drying temperature. Best drying condition required sequential reduction in temperature (120 to 50 degrees C) resulting in good color retention. This reduced batch time to 4 h compared to 6 h batch of conventional isothermal drying at 50 degrees C.