The aim of this research is to investigate the effects of brown algae to solution ratio, feed rate, and pH on the multiple responses of Sargassum cristaefolium alginate extracted using twin screw extruder. Box-Behnken design was used to find out the optimum extrusion-assisted extraction parameters based on the responses of residence time distribution (RTD), yield, intrinsic viscosity, and molecular weight. The result showed that alginate extrusion-assisted extraction parameters affected on the movement of algae in the screw channel and physicochemical properties of S. cristaefolium alginate. The alginate extrusion-assisted extraction parameters have quadratic effect on the responses of RTD, yield, intrinsic viscosity and molecular weight. The predicted values at the optimum extrusion parameters as independent variables are the use of brown algae to solution ratio (3.11), feed rate (2.95 rpm), and pH 10.3. The M/G ratio of S. cristaefolium alginate based on fractions analysis is 0.29 (M/G ratio < 1), indicating that S. cristaefolium alginate contains guluronate fraction of 77.10% and manuronate fraction of 22.90%. Intrinsic viscosity of S. cristaefolium alginate in aqueous solution was determined and shown shear-thinning pseudoplastic.
Keywords: Alginate; M/G ratio; Response surface method; Rheology; Sargassum cristaefolium; Twin-screw extruder.