Adsorption of cationic potato starch on microcrystalline cellulose

Abstract

Abstract The adsorption of cationic potato starch on microcrystalline cellulose was investigated taking into account that starch is a mixture of amylose and amylopectin. The separate adsorption of both components could be calculated by determining starch concentrations twice using two methods having a different sensitivity for amylose and amylopectin. It was found that cationic amylose adsorbs preferentially. The preferential adsorption is probably related to the porous nature of microcrystalline cellulose. The smaller and linear amylose molecules are able to penetrate the pores, while the much larger and branched amylopectin molecules have only access to the exterior surface. The effects of monovalent and divalent electrolytes, pH and degree of substitution (DS) on the adsorption were investigated. The adsorption was found to decrease with increasing electrolyte concentration, the divalent cations being ten times as effective in suppressing the adsorption as the monovalent cations. Increasing the surface charge by increasing the pH led to higher adsorption. The effect of DS depended on the electrolyte concentration: at low electrolyte concentration the adsorbed amount was largest for the cationic starch with the lowest DS, whereas at higher electrolyte concentration starch with the highest DS adsorbed better. These effects can be explained with a recent theory on polyelectrolyte adsorption.