Chain length distribution of inulin from dahlia tubers as influenced by the extraction method

Abstract

A variety of fructans occurs in plants, having various configuration and chain lengths from 3 up to a few hundred fructose units. The structurally simplest fructan is a linear inulin, where the fructose units are linked by β- 2,1 bonds, present mostly in Asteraceae and Cichorioideae (e.g. dahlia). The pharmacological effects of fructans depend mainly on the degree of polymerization (DP). Hence, a controlled DP distribution profile is essential for the expected spectrum of pharmacological activities. The aim of this study was to purify fructans from dahlia (Dahlia x hortensis Guill. cv.‘Ken’s Flame’) tubers with different inulin chain lengths profile. We developed the selective preparative approach, followed by qualitative and quantitative analyses by pulsed amperometry-high performance anion-exchange chromatography. The fructans were obtained by the extraction of dahlia tubers with water, concentrated under vacuum, subsequent precipitation of carbohydrate fraction by ethanol, followed by purification using four different combinations of absorbents such as Dowex® ion-exchange resin, aluminium oxide, calcium carbonate, and activated carbon. The highest content of short-chain inulin (38%) was in the crude fraction and after the separation on Al2O3 and CaCO3. All methods selectively enriched inulin in the middle-length chains. The highest concentration of high-quality longchain inulin (16%) was obtained by consecutive washing through CaCO3, Al2O3, Dowex, and charcoal. This complex was also the most balanced in terms of the proportion among short-, medium-, and long-chain inulin (33%, 43%, and 16%, respectively).