Clarifications of stevia extract using cross flow ultrafiltration and concentration by nanofiltration

Abstract

Cross flow ultrafiltration was employed to clarify the pretreated stevia extract. Two practical modes of cross flow ultrafiltration, namely, steady state under total recycle mode and batch concentration mode, were used. A detailed investigation of effects of the operating conditions on the permeate flux and permeate quality was undertaken. It was observed that the significant flux enhancement was achieved with transmembrane pressure drop and cross flow rate. Maximum 200% flux enhancement with cross flow rate and 140% with transmembrane pressure drop were attained in the range of operating conditions studied herein. Effects of cross flow rate on the permeate properties were marginal but that of the transmembrane pressure drop was significant. Recovery of stevioside in the permeate was in the range of 30–56% for various transmembrane pressure drop and it was maximum for lower operating pressure, 276kPa. However, the recovery of stevioside decreased to 38% at 276kPa pressure after 10h of operation. Nanofiltration was employed to concentrate the ultrafiltered liquor. During nanofiltration, the ultrafiltered feed was concentrated maximum twice at 1241kPa and 1500rpm of stirrer speed within 1h of operation. Maximum overall (ultrafiltration followed by nanofiltration) purity and recovery of 60% is obtained for a particular set of operating conditions.