Kinetics of moisture adsorption during simulated storage of whole dry cocoa beans at various relative humidities

Abstract

A simple combined model involving semi-infinite slab geometry with Fickian diffusion and the Harkin-Jura adsorption isotherm, adjusted to the final equilibrium experimental moisture content given by the model, was developed to predict the kinetics of moisture adsorption of dried cocoa beans under simulated external storage temperature and relative humidity. This model was able to predict accurately the moisture gain by individual beans during storage (R2 > 0.994). Experimental moisture adsorption kinetics of whole cocoa beans were determined for a relative humidity range of 64–93% at 25 °C (298 K). A diffusion coefficient at 298 K of 3.30 × 10−11 ± 0.56 × 10−11 m2/s was determined and found independent of moisture concentration in the experimental range considered. An operational storage map was proposed to predict the average moisture content of whole cocoa beans of any commercial thickness (0.600 ≤ l ≤ 1.200 cm) (6.00 × 10−3 ≤ l ≤ 1.200 × 10−2 m) during storage under atmospheres of constant relative humidity (64% ≤ RH ≤ 93%) and temperatures from 5 to 35 °C (278–308 K).