Potential of ultrafiltration for separation and purification of ellagitannins in blackberry (Rubus adenotrichus Schltdl.) juice

Tropical highland blackberry is characterized by its high content of ellagitannins, which are considered to be potentially beneficial for human health, but relatively rare in food sources. Due to its relatively high molecular weight, the feasibility of selective separation of ellagitannins by ultrafiltration was assessed on clarified tropical highland blackberry juice. Six organic tight ultrafiltration membranes with nominal molecular weight cut-off (MWCO) ranging from 1 to 150 kDa were tested. Filtration temperature was set constant to 30 degrees C, cross-flow velocity to 0.3 m s(-1) and transmembrane pressures varied at 0.5, 1, 1.5, 2 and 3 MPa, for each membrane tested. Experiments were performed at a constant volumetric reduction ratio (1 < VRR < 1.1) and quantitative analyses of total ellagitannins and anthocyanins were determined by HPLC/DAD. Retention of ellagitannins reached 100% for all membranes except for that showing a nominal MWCO of 150 kDa, when transmembrane pressure was over 1 MPa. Retention of total anthocyanins increased with transmembrane pressure and reached values over 90% for all membranes tested at 3 MPa. A membrane with a nominal MWCO of 2 kDa presented the highest anthocyanin flux at 2 MPa and thus appeared to be the most promising for fractionation of the polyphenolic compounds. A model used to predict total ellagitannin purification with constant volume diafiltration confirmed that this membrane presented one of the lowest diavolumes needed to achieve a purity of 90% at higher transmembrane pressures. (C) 2014 Elsevier B.V. All rights reserved.