Triple Enzymatic Cascade Reaction to Produce Hydroxytyrosol Acetate from Olive Leaves Using Integrated Membrane Bioreactors

An integrated system of three membrane bioreactors (MBRs) has been developed that cascades three different enzymatic reactions. The integrated system was applied to produce hydroxytyrosol acetate from oleuropein extracted from olive leaves. Different reactor configurations for each reaction were tested and individually optimized to select the MBR to ensure high conversion and continuous production of oleuropein aglycone (OA), hydroxytyrosol (HY) and hydroxytyrosol acetate (HA). Based on this study, the most performing configuration of the integrated system was identified. In the first reaction, oleuropein was converted to OA using a biocatalytic membrane reactor (BMR) with immobilized β-glucosidase in polymeric membranes (conversion 95 %). The OA was then fed to another BMR, where it was converted to HY (conversion: 70 %) by an immobilized mutant of the promiscuous hydrolase/acyltransferase (PestE) (from the thermophilic archaeon Pyrobaculum calidifontis VA1). The HY produced was then acetylated using PestE immobilized on magnetic nanoparticles in a multiphase MBR (conversion: 98 %) and simultaneously extracted (extraction: 98 %) in ethyl acetate. The work demonstrates that continuous cascade enzymatic reactions can be engineered using artificial membranes to tailor enzyme compartmentalization, mass transport and phase contact according to reaction requirements. Besides, environmental factors proved the sustainability of the integrated membrane bioreactive system.