Physicochemical Studies on the Biopolymer Inulin: A Critical Evaluation of Its Self-Aggregation, Aggregate-Morphology, Interaction with Water, and Thermal Stability Abhijit Dan, Soumen Ghosh, Satya P. Moulik Centre for Surface Science, Department of Chemistry, Jadavpur University, Kolkata 700032, India Received 22 November 2008; revised 12 March 2009; accepted 31 March 2009 Published online 7 April 2009 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/bip.21199 This article was originally published online as an accepted preprint. The ‘‘Published Online’’ date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley. com INTRODUCTION I nulin is a polydisperse polysaccharide consisting almost exclusively of b (2?1) fructosyl fructose units (Scheme 1). It was first isolated from the plant Inula helenium, 1 and was later found to occur in several plants as reserve polysaccharide. X-ray diffraction studies have revealed orthorhombic and pseudo-hexagonal geometry for the hydrated and semi-hydrated (half a molecule of water per fructosyl unit) inulin, respectively, consisting of two anti- parallel six-fold helices. 2 A model corresponding to five-fold Physicochemical Studies on the Biopolymer Inulin: A Critical Evaluation of Its Self-Aggregation, Aggregate-Morphology, Interaction with Water, and Thermal Stability Correspondence to: Satya Moulik; e-mail: spmcss@yahoo.com ABSTRACT: Physicochemical properties viz., aggregation, molar mass, shape, and size of chicory inulin in solution were determined by fluorimetry, DLS, SLS, TEM, and viscometry methods. The thermal stability of the biopolymer was examined by TGA, DTA, and DSC measurements. The water vapor adsorption of desiccated inulin was also studied by the isopiestic method, and the data were analyzed in the light of the BET equation. On the basis of the obstruction to ion conductance by the inulin aggregates in solution and analysis of the data, the extent of hydration of inulin in solution was estimated. The result was coupled with the intrinsic viscosity, [h], of inulin to ascertain the shape of the biopolymer aggregates in aqueous solution. The critical aggregation concentration (cac) of inulin in aqueous as well as in salt solution was assessed by fluorimetry. The weight average molar mass, M w , of inulin monomer and its aggregate was found to be 4468 and 1.03 3 10 6 g/mol, respectively, in aqueous solution. This aggregated mass was 2.4 3 10 6 g/mol in 0.5M NH 4 SCN solution. The [h] values of the soft supramolecular aggregates in solution (without and with salt) were small and comparable with globular proteins evidencing spherical geometry of the biopolymer aggregates as supported by the TEM results. In DMSO, rod-like aggregates of inulin was found by the TEM study. The [h] of the biopolymer in the DMSO medium was therefore, higher than that in the aqueous medium. Unlike aqueous medium, the aggregation in DMSO was not associated with a cac. # 2009 Wiley Periodicals, Inc. Biopolymers 91: 687–699, 2009. Keywords: inulin; aggregation; critical aggregation concentration; molar mass; intrinsic viscosity; aggregate shape; hydration; thermal stability Contract grant sponsor: FAST Track Contract grant number: SR/FTP/CS-35/2006 V V C 2009 Wiley Periodicals, Inc. Biopolymers Volume 91 / Number 9 687