Cyclically pressurized extraction of solutes from ground coffee: Kinetic experiments and modeling

The main aim of this study was to investigate the influence of pressure and pressure cycles on the kinetics of solute removal from ground coffee. Extraction experiments were performed with water at a low temperature (≈17 °C) in the pressure range from 91.4 kPa to 338.2 kPa for 25,200 s. A semi-empirical pure diffusive and a hybrid diffusive-convective model described correctly the transient experimental extraction curves at constant and cyclic pressurized conditions, respectively. With 80% of probability the modeling approach supports, and explains in terms of transport phenomena, the significant positive effect of the examined factors on the kinetics of extraction. According to it, the rise of pressure increases the diffusivity, while the pressure cycles cause a movement of fluid through the solid microchannels and consequent solute transfer by convection. Coffee lipids were also extracted under constant and cyclic pressurized conditions with a polar (water) and a nonpolar (chloroform) solvent. The negligible fraction of total lipids in the aqueous phase at equilibrium refutes an important alleged advantage of hydrostatic pressure cycling extraction, that is, it extracts insoluble compounds. Moreover, a non-significant influence of pressure and pressure cycles (p > 0.02) on total extracted lipids at equilibrium was observed when using chloroform.