Drying-toasting kinetics of presoaked soybean in fluidised bed. Experimental study and mathematical modelling with analytical solutions

The aim of this work was to study the mass transfer kinetics during fluidised-bed drying-toasting of soaked soybean to provide design information for production of whole soybean snack. The experimental work consisted of determinations of thin layer drying-toasting curves of soaked soybeans in a fluidised-bed dryer at air temperatures between 100 and 160 °C, for 60 min, using an air velocity of 2.5 m/s. The analytical solution for short times was not suitable for this high temperature process. In contrast, calculations by complete analytical solution for constant diffusion coefficient (Deff) and constant radius (R0), an infinite convergent series, were markedly accurate. However, previous studies on particle density and volume revealed non-negligible shrinkage during drying-toasting, possibly caused by the fact that the ratio of Deff to R2 remains substantially unaltered. Values of the diffusion coefficient (around 10−9 m2/s) and activation energy (31 kJ/mol) are within the ranges expected for food drying at elevated temperatures.