Hydrostatic pressure cycling extraction of soluble matter from mate leaves Original Research Article

The main aim of this study was to investigate the kinetics of solid–liquid extraction of soluble matter from leaves of Ilex paraguariensis assisted by pulsed hydrostatic pressure. A large set of experiments was carried out involving a mixture of distilled water and comminute leaves of mate fed in a batch extractor kept at approximately 16.7 °C. The influence of pressure on equilibrium solute concentrations and rate of extraction was examined in the pressure range from 91.4 to 338.2 kPa by applying or not hydrostatic pressure cycles. Whatever the case a significant increase of such responses with direct positive impact on extraction yield and time of extraction was experimentally observed by changing the investigated factor (e.g.; the extraction yield was increased from ≈13% at 91.4 kPa to approximately 34% and the time to have 90% of the highest efficiency was reduced from ≈17,000 s at 91.4 kPa to ≈6000 s by applying hydrostatic pressure pulses at only 338.2 kPa). An hybrid diffusive–convective model was suggested to represent the transient extraction of soluble compounds from the discoid particles. The classical Fick’s law described the two-dimensional diffusion for the static long periods of mass transfer at constant pressure, while a model dependent on the gamma function computed the fraction of solute periodically extracted by convection from the internal solid microchannels during the rapid pulses of hydrostatic decompression. For all the investigated conditions the proposed analytical model well reproduced the kinetic experimental results of solute mass fraction in the solid and liquid phase.