Modeling thin layer drying-roasting kinetics of soaked quinoa

Abstract

Quinoa has higher protein content (11-16% m/m) and better amino acid profile than most cereals and represents a valuable resource for healthy nutrition. This work studied the kinetics of mass and energy transfer during fluidised thin layer drying-roasting of soaked and washed quinoa, a treatment suitable for preparing a ready-to-eat food. Curves describing moisture content and temperature behaviour with time were obtained for temperatures of 80, 100, 120, and 140 ºC and air velocity of 0.8 m s^-1. A coupled mass and energy model was proposed to describe the curves mathematically. The model consisted of a pair of ordinary differential equations (ODEs): a transient macroscopic energy balance equation for heat transfer and either a short or a long dimensionless time mass transfer equation. The model was used to determine the effective diffusion coefficient proposed as an Arrhenius function of temperature by utilising the whole dataset. The heat transfer coefficient was estimated from a correlation reported earlier with values ranging from 164 to 179 W m^-2 ºC^-1. The activation energy and pre-exponential factor were fitted using a combined method involving a numerical integration of the ODE system followed by a parameter optimisation algorithm. Values obtained were E_a = 39.9 kJ mol^-1 and, D₀ = 2.872 x 10^-4m² s^-1, respectively. Predicted moisture content and temperatures agreed well with experimental values. The present research could be extended to deep fluidised bed models to help optimise existing equipment or design new.