Mass transfer kinetics of biologically active compounds from Propolis

The present investigation is provoked by the increasing interest in propolis as a source of biologically active compounds (BAC) and the great differences in contact times, reported in literature, for their extraction by an ethanolic solvent. Two sets of kinetic investigations are performed: - Liquid phase kinetic curves are obtained by spectrophotometric analysis of the extract (total polyphenols, flavones and flavonols, flavanones and dihydroflavonols). The total yield is determined gravimetrically. - Size evolution of the propolis particles during extraction is continuously monitored by microscopy connected with a photo camera. The effect of the liquid/solid ratio and the stirring intensity is studied. The result confirm that BAC release proceeds faster than usual solid-liquid extraction, because of the partial dissolution of the kind matrix, as well as the destruction to smaller particles, due to the particulate character of the propolis material. The effective mass transfer coefficient is of the order of 10(-6) m/s. Favourable conditions for process performance are found.