Extraction of steviol glycosides using novel cellulose acetate pthalate (CAP) – Polyacrylonitrile blend membranes

• Blend membranes are applied for glycoside extraction.
• Resultant membrane is strongly hydrophilic.
• Various resistances were analyzed for filtration of stevia extract.
• Optimum membrane was selected in terms of flux, recovery and purity.
• Optimum flux, recovery and purity were 11 L/m2 h, 68% and 34%, respectively.

Tailor made membranes cast from blend of cellulose-acetate pthalate (CAP) and polyacrylonitrile (PAN) polymers for the extraction of steviol glycosides is the point of focus of this study. The mentioned blend is a highly non-ideal and immiscible and membranes formed using this blend is not reported in the literature. Various weight percent combinations of the polymers were dissolved in an aprotic solvent, viz., dimethylacetamide (DMAc) and membranes were cast using the phase inversion method. The obtained membranes were characterized on basis of molecular weight cut off (MWCO), hydraulic permeability, hydrophilicity, pore density, porosity, surface morphology and mechanical strength. It was found that a set of membranes of various MWCO was obtained ranging from 7 kDa to 104 kDa for various compositions of the blend. Stevioside and Rebaudioside were then recovered from water extract of dry Stevia leaf powder using these ultrafiltration membranes. The permeate flux decline was analyzed for each of the membranes, to study the fouling characteristics. The optimum membrane was identified in terms of steady state permeate flux, recovery and purity of glycosides. It was found that the 90 kDa membrane yielded the maximum steady state flux of 11 L/m2 hr, recovery of 68% and purity of 34%.