Solvent extraction of rosmarinic acid from lemon balm and concentration of extracts by nanofiltration: Effect of plant pre-treatment by supercritical carbon dioxide

The present work investigates a complex scheme of valuable components extraction from herbs and extracts concentration by nanofiltration. Two ethanol–water mixtures (50:50 and 80:20 (v/v)) have been used for solvent extraction of rosmarinic acid (RA) from dry lemon balm aerial parts and high recovery (up to 94%) has been obtained in three steps scheme. A positive impact of a preliminary treatment by supercritical CO2 (in order to utilize the plant essential oil) on the successive RA extraction has been observed. The cross-linked polyimide membrane Duramem™ 200 has performed RA rejection of over 99% and reasonable flux at dead end nanofiltration pressure of 30 bar. This high rejection being independent of ethanol content in the solvent, supercritical pretreatment and RA concentration of the extracts has allowed to obtain nearly saturated retentate solutions (up to 19 g/L RA) and to reuse the permeates for lemon balm extraction in place of pure solvent. A RA content in the extracts dried total solid mass of 28 ± 2 % has been achieved.The additional resistance due to osmotic pressure difference and concentration polarization has been determined as a power function of retentate concentration with power value near to unity and approximately similar for the extracts and a model solution of RA.The study has confirmed the potential benefits of nanofiltration implementation in herbal extracts processing.

► An advantageous complex processing of Lemon balm is considered.
► Supercritical CO2 pretreatment recovers essential oil and improves the next steps.
► The ethanol removal of rosmarinic acid from plant residue is facilitated.
► Nanofiltration of its extracts results in retentates concentrated near to saturation.
► The permeates can be reused and extraction steps increased.