Diffusion of water and caffeine in coffee beans using the hemispherical geometry approach

摘要

Geometrical, morphological, and shape factors are crucial for the accurate prediction of mass transfer rate of caffeine and water in the extraction of caffeine in aqueous medium from coffee beans. A new expression for the sphericity was deduced considering the hydrated coffee bean as a triaxial semilipsoid with moving boundaries applied to a nonsteady state analytical solution to describe the diffusion phenomena for the hemispherical geometry to best represent the morphology of the coffee bean during the caffeine extraction at varying temperatures from 30 to 60 degrees C. The sphericity increases with moisture in a power law trend. The hemisphere mathematical model presented an excellent adjustment to the data, with diffusion coefficients between 1.03 x.10(-11) and 9.00 x.10(-10) m(2)/s for caffeine and 0.69 x.10(-10) and 2.03 x.10(-10) m(2)/s for water; strongly influenced by temperature with activation energy of 59.93 and 41.24 kJ/mol, respectively, for caffeine and water.