Selecting ultrafiltration and nanofiltration membranes to concentrate anthocyanins from roselle extract (Hibiscus sabdariffa L.)

Abstract

Ten nanofiltration flat-sheet membranes and eight tight ultrafiltration membranes with nominal MWCOs ranging from 0.2 to 150kDa were tested to concentrate anthocyanin extract from roselle. A pilot system was used, which featured a membrane cell with an effective area of 0.0155m2. Permeate fluxes were recorded for transmembrane pressures between 0.5 and 3.0MPa, while keeping all other operating conditions constant (volumetric reduction ratio 1, 35°C). Retention values of total soluble solids, acidity and anthocyanins increased with transmembrane pressure. With similar permeate fluxes at average transmembrane pressure, retention of anthocyanins is significantly higher for nanofiltration membranes than for ultrafiltration membranes. A membrane was then selected for an industrial trial on the basis of its flux, retention of compounds of interest and energy consumption per liter of permeate. The trial using a 2.5-m2 filtration surface, could concentrate roselle extract from 4 to 25g total soluble solids per 100g, with 100% retention of anthocyanins. No significant damages were observed when comparing concentrate quality with the initial roselle extract. © 2011 Elsevier Ltd.