Drying-toasting kinetics of soaked soybeans in fluidized bed

TORREZ IRIGOYEN,RICARDO MARTIN; GINER, SERGIO ADRIÁN

Foz de Iguazú

Congreso; 16th World Congress of Food Science and Technology – IUFoST; 2012

Most food engineering studies on soybean dealt with postharvest drying or heat-inactivation processes. In this work, mass transfer kinetics was studied during fluidized-bed drying-toasting of pre-soaked soybean to improve the understanding of a process devised to produce a whole grain snack. The aim was to develop a mathematical model that considers shrinkage along the process. Thin layer drying-toasting curves of soaked soybeans in a fluidized-bed dryer (air velocity, 2.5 m/s) were conducted at temperatures between 100°C and 160°C, for 60 min. The moisture contents as a function of time were accurately predicted by the analytical series solution of unsteady-state diffusion for a sphere with internal control, considering constant diffusion coefficient (Deff) and product radius Rp (r2=0.991). An Arrhenius dependency of Deff with temperature was found with a preexponential factor of 3.483 x 10-5 m2/s and an activation energy of 31.4 kJ/mol (r2=0.991). As previous studies revealed a considerable product shrinkage, these predictions were unexpectedly accurate. The possible cause is that the Deff/Rp2 ratio may have remained substantially constant during drying-toasting. With this relationship in mind, a more accurate model could be proposed which considers shrinkage and variable Deff. The partial-differential equation model obtained was solved using volumetric water concentration units as dependent variable by an implicit finite-difference numerical method, introducing a time-varying mesh with equal-volume elements for increased accuracy. Predictions were highly satisfactory, conferring this method great potential for applications in food processes involving structural changes.