Fractionation of starch hydrolysate into dextrin fractions with low dispersity by gradient alcohol precipitation

Abstract

Gradient alcohol precipitation was established as a fractionation method, and used for fractionating the 1-butanol-HCl-hydrolyzed cassava starch into dextrin fractions with a narrower molecular weight distribution. The addition of alcohol may have led to very high alcohol concentration in some parts of the dextrin solution, which may have impeded the fractionation process. Therefore, the rate of alcohol addition should be rigorously controlled during fractionation. The effects of the alcohol type and the initial dextrin concentration on fractionation were studied using the molecular-weight dispersity (DM) as index. The parent dextrin was fractionated by gradient alcohol precipitation into seven fractions with decreasing DM, with the volume ratios of the dextrin solution to alcohol at 4:1, 2:1, 1:1, 1:2, 1:3, 1:4, and 1:5, respectively. The better fractionation effect of different alcohols was in the order of methanol>ethanol>isopropanol; whereas the dextrin yield by these alcohols was in the reverse order. Furthermore, the peak molecular weight of each fraction tended to decrease with an increase in the alcohol concentration at which it was precipitated. The optimal initial concentration was in the range of 1.8%–2.7%, and lower or higher concentrations resulted in inferior fractionation. These results suggest that gradient alcohol precipitation is an efficient method for fractionating dextrin into fractions with different molar masses of low DM, which would allow dextrin fractions to be tailor-made for specific application.