Integration of solvent extraction and membrane processes to produce an oleuropein extract from olive leaves

• Extraction solvent was applied for extracting phenolic compounds from olive leaves. • Temperature, solvent/solid, and time were optimized using an experimental design. • The extract was subjected to ultrafiltration (UF) followed by nanofiltration (NF). • Polyphenols, flavonoids and total antioxidant activity rejections were analyzed. • An extract enriched in oleuropein was obtained from the NF retentate. The integration of solvent extraction and membrane separation technology was used to recover and concentrate oleuropein from olive leaves. In this study, the effect of extraction solvent (type, composition) on the content of total phenolic compounds (TPC) extracted from olive leaves was investigated. Experimental results showed that ethanol:water, 75 %/25 % (v/v), gives the highest TPC. Thus, to establish the parameters to obtain hydroethanolic olive leaves extract with the highest content of total phenolic compounds, a Central Composite Design was performed. The extract obtained at 50 °C for 90 min, within 0.03 g/ml, was subjected to crossflow ultrafiltration (UF) to remove suspended solids in the feed and to reduce fouling phenomena, followed by a stirred dead-end nanofiltration (NF) using a commercial flat sheet membrane at different pressure (10, 20 and 30 bar). The nanofiltration (at 30 bar) showed a high rejection coefficient towards phenolic compounds and flavonoid contents. Fractions coming from UF and NF (at 30 bar) revealed that the highest content of oleuropein was 119.01 mg/g corresponding to NF retentate, high antioxidant capacity (DPPH method). Conductivity, sanity, turbidity, pH, TDS, and TSS of different fractions were also determined. It can be concluded that the integration of solvent extraction and membrane separation technology is efficient for the recovery and concentration of oleuropein and phenolic compounds from olive leaves. The obtained concentrate is of interest for preparing formulations to be used in the food, cosmetic and pharmaceutical industries.