Separation of Rebaudioside-A from stevia extract: Membrane selection, assessment of permeate quality and fouling behavior in laminar flow regime

Abstract

This study is aimed to purify Rebaudioside-A (Reb-A) from aqueous stevia extract by ultrafiltration both in batch and cross flow operations. Performance of four different polyether-sulfone membranes of molecular weight cut off 10, 20, 30 and 50kDa was investigated for permeate flux and quality in terms of its color, clarity, total solid, purity and selectivity. Hermia’s fouling models, namely, complete, standard, intermediate pore blocking and cake filtration have been tested for their fitness in flux decline regime. 30kDa membrane was found to be the most effective for Reb-A separation. The effect of transmembrane pressure (TMP) drops and Re numbers on the permeate flux and quality in cross flow process were investigated. Steady state permeate flux increased with TMP drops and flow rate. Purity and selectivity of Reb-A in permeates also increased with TMP drops and flow rates. TMP drop of 414kPa and Re number of 1667 were found to be most suitable operative conditions with selectivity of 0.45 and flux value of 5.86×10−6m3m−2s−1. Individual fouling model could not fit entire flux decline data; however, combination of two models well described the flux profile. Cake filtration showed best fitting under the operating conditions.