Enrichment of Higher Molecular Weight Fractions in Inulin FRANK T. MOERMAN,* ,† MARINELLA B. VAN LEEUWEN, ‡ AND JAN A. DELCOUR † Faculty of Agricultural and Applied Biological Sciences, Laboratory of Food Chemistry, K.U. Leuven, Kasteelpark Arenberg 20, B-3001 Heverlee, Belgium, and Agrotechnological Research Institute ATO BV, Bornsesteeg 59, P.O. Box 17, NL-6700 AA Wageningen, The Netherlands Inulin (general formulas GF n and F m , with G ) anhydroglucose and F ) anhydrofructose) naturally occurs as a homologous series of oligo- and polysaccharides with different chain lengths. For reasons of growing interest in the food and pet food industries, the short chain inulins have to be separated from their long chain analogues because their properties (digestibility, prebiotic activity and health promoting potential, caloric value, sweetening power, water binding capacity, etc.) differ substantially. To study these properties in relation to the number average degree of polymerization (DP n ), ultrafiltration, specific crystallization from aqueous solution, and precipitation from solvent/water mixtures were used to enrich native chicory and dahlia inulin in the higher molecular weight fractions. Depending on the membrane module used, the DP n of chicory inulin (DP n ) 8.1) and dahlia inulin (DP n ) 29) could be increased by ultrafiltration to a maximum value of, respectively, 22 and 43. With crystallization from aqueous solutions (25 °C), similar results were obtained but at a much higher yield. Finally, long chain inulin could be precipitated from aqueous solutions in the presence of high concentrations of methanol, ethanol, and acetone. Acetone demonstrated to be the best solvent system to increase the DP n , followed by ethanol and methanol. However, for safety reasons and food purposes, ethanol was evaluated to be the best choice. With ethanol, the DP n could be raised to 25 for chicory inulin and up to 40 for dahlia inulin. KEYWORDS: Inulin; chicory; dahlia; number average degree of polymerization; DP n; ultrafiltration; crystallization; solvent precipitation INTRODUCTION Inulin obtained from several Compositae (Jerusalem arti- chokes, artichokes, chicory, dahlias, and dandelions) is a subject of interest in many food and “agrification” research programs (1-5). Recently also, enzymatic in vitro synthesis processes starting from sucrose have been developed, and several bacteria and fungi are examined for their potential to synthesize fructans that are in almost all cases of the levan type (4). The only bacterial species known to produce an inulin type fructan is Streptococcus mutans. Inulin naturally occurs as a homologous series of oligo- and polysaccharides of different lengths made up of -2,1-linked anhydrofructofuranosyl units (F) that are in most cases terminated with an anhydroglucopyranosyl residue (G). This anhydroglucose unit is linked to the reducing end of the fructan chain by means of an R-1,2 bond. Inulin (with less than 2% branching, mainly branches of -2,6-linked anhydro- fructose units) can thus generally be represented, depending on the terminal carbohydrate unit, by the general formulas GF n and F m . Therein, G represents a glucose unit, F represents a fructose unit, n is an integer representing the number of fructose units linked to the terminal glucose unit, and m is an integer representing the number of fructose units linked to each other in the carbohydrate chain. The numbers n + 1 and m, respectively, indicate the degree of polymerization (DP) of the inulin molecule. As inulin is a polydisperse mixture of oligomers with varying DPs, inulin samples are characterized by the number average degree of polymerization, DP n . For reasons of growing interest in the food and pet food industries, the short chain inulins have to be separated from their long chain analogues, because their properties (digestibility, prebiotic activity and health promoting potential, caloric value, sweetening power, water binding capacity, etc.) differ substan- tially (5-7). To get insight into the unique properties of polymeric inulin in relation to its DP, several fractionation procedures are examined for their potential to enrich high molecular weight fractions. A series of scientifically described methods known to increase DP of polysaccharides are studied as follows: ultrafiltration, specific precipitation/crystallization from aqueous solutions (3), and specific precipitation through addition of a solvent, which decreases inulin solubility (8-10). Comparisons are made in the average DP obtained, the process yield, and the process complexity. MATERIALS AND METHODS Materials. Standard grade chicory inulin (Standard grade inulin is inulin obtained from plants or plant parts through conventional * To whom correspondence should be addressed. Tel: ++32-9-386 65 44. E-mail: fmoerman@skynet.be. † Laboratory of Food Chemistry. ‡ Agrotechnological Research Institute ATO BV. 3780 J. Agric. Food Chem. 2004, 52, 3780-3783 10.1021/jf030590v CCC: $27.50 © 2004 American Chemical Society Published on Web 05/22/2004