Determination of characteristic properties of mulatto beans (Phaseolus vulgaris L.) during convective drying

Abstract

Abstract Mulatto beans (Phaseolus vulgaris L.) require proper drying for safe transport and storage. To support the drying process design, the objective of this work was to determine the mass transfer and thermodynamic properties of mulatto bean. Mulatto beans were dried under different convective conditions from an initial moisture content of 25% (w.b.) until its equilibrium drying. Using fundamental and empirical models, and considering the bean as a sphere, drying constants and the effective diffusivity of the moisture inside the product was determined at each temperature. Then, using an Arrhenius type equation, effective diffusivity values for each temperature were modeled, and the activation energy was determined along with other thermodynamic properties. Results revealed that effective diffusivity presented values typical of non-porous protein/starchy foods and varied from 4.11 × 10−11 for 40 °C and 8.72 × 10−11 m2s−1 for 70 °C. The activation energy confirmed that effective diffusivity is highly dependent on temperature with values ranging from 21.13 to 22.23 kJ mol−1, indicating liquid diffusion within the food material. Enthalpy, entropy, and Gibbs free energy also indicate that the process is endothermic and non-spontaneous. From a practical point of view, it is concluded that mulatto beans have a diffusion-controlled drying requiring thin layers of material for effective drying.