Membrane concentration of antioxidants from Castanea sativa leaves aqueous extracts

Aqueous extraction of Castanea sativa leaves (CsL) was scaled up and the extract was processed in a series of two UF membranes (5 and 10 kDa) with the aim of concentrating the active phenolic compounds with antioxidant activity. Due to the occurrence of adsorptive fouling of the phenolic compounds found in one membrane's configuration assayed (Configuration I), batch dilution of the retentate was required for optimal performance. However, this strategy did not improve the selectivity of the process and the active compounds were diluted. The best prediction of the permeate flux was provides by the cake layer formation model (CFM) to the 5 kDa membrane and by the standard pore blocking model (SBM) to the 10 kDa membrane when the Configuration II was assayed. Secuencial filtration without dilution of the 5 kDa permeate (Configuration I) provides a selective separation of active compounds on 10 kDa membrane filtration process. The final concentrated extracts presented radical scavenging capacities comparable to Trolox and to BHA. The test with reconstituted human epidermis (Episkin®) confirmed that the extracts were non irritant at 1%. Operation with reutilization of the permeate was feasible and the extraction yield of active compounds was not significantly affected. Due to the non selective retention of phenolic and soluble protein, the separation of this latter by ethanol precipitation was proposed. The ethanol precipitation of concentrates streams increased its purity and activity of the final products by about 15%.

► Ultrafiltration–diafiltration process with PES membranes increased the antioxidant properties of concentrated streams.
► Ethanol precipitation increased purity and activity of the final products by about 15%.
► Antioxidant capacity of final products were screened using scavengers, chelating and oil emulsion stabilizing assays.
► Castanea sativa leaf extract at 1% is non irritant in the test with reconstituted human epidermis (Episkin®).