FOOD HYDROCOLLOIDS Food Hydrocolloids 21 (2007) 683–692 Investigation of equilibrium solubility of a carob galactomannan M.A. Pollard à , R. Kelly, C. Wahl, P. Fischer à , E. Windhab, B. Eder, R. Amado´ Laboratory of Food Process Engineering and Laboratory of Food Chemistry, Institute for Food Science and Nutrition, Swiss Federal Institute of Technology, 8092 Zu ¨ rich, Switzerland Received 31 May 2006; accepted 14 August 2006 Abstract The equilibrium aqueous solubility of a commercial carob flour was investigated by determining the percentage of soluble and insoluble components as a function of dissolution temperature. The cumulative polysaccharide yield was ca. 50% at 5 1C, increasing approximately as a linear function of temperature to ca. 90% at 85 1C. Overall molecular weight and intrinsic viscosity of the soluble polysaccharide were determined by size-exclusion chromatography. With increasing dissolution temperature, there was weak trend towards higher overall molecular weight and intrinsic viscosity: M w from 1060 to 1150 kg/mol, and [Z] from 11.8 to 12.5 dl/g, between 5 and 65 1C, respectively. Broad, amorphous peaks were evident in the wide-angle X-ray scattering profiles, indicating no role for polysaccharide melting. The continuous increase of molecular weight and decrease of DS gal with dissolution temperature is interpreted as the result of thermodynamic partitioning based on a classical polymer-solvent fractionation, a mechanism that applies only for polysaccharide components with DS gal o0.35 within the accessible temperature range. r 2006 Elsevier Ltd. All rights reserved. Keywords: Locust bean gum; Carob; Galactomannan; Phase behavior; Fractionation 1. Introduction Carob galactomannans are nonionic, linear polysacchar- ides used as thickeners/stabilizers, co-gellants, and fat replacers in ice creams, sauces, and other food products. The functional polysaccharide is a poly((1–4)-b-D-man- nose) having degree of polymerization 1000, with a statistical distribution of single-unit (1–6)-a-D-galactose side groups. This polysaccharide is present as enlarged deposits present in the endosperm of mature carob (locust bean) seeds, and are borne in the tree’s fruit. The seeds are industrially processed by hull cracking, sifting, and milling operations to isolate and grind the endosperms, which are then sold as a crude flour. Commercially sold flours are reported to contain about 85% pure galactomannan on a mass basis and make an important contribution to the hydrocolloid usage in many food products. Locust bean gum is regarded as essential for providing ‘texture’ (thus far poorly understood) to premium ice creams for instance. Several reviews are available (Ross-Murphy, 1995; Scher- bukhin & Anulov, 1999; Srivastava & Kapoor, 2005). One of the most important characteristics of the molecular structure of the galactomannan polysaccharide family is the galactose substituents, quantified as an average degree of substitution, DS Gal . Without these groups present in some concentration the isolated poly- saccharide is unstable in solution and either crystallizes or precipitates. Galactomannans with DS Gal generally above 0.4 such as guar (DS Gal ¼ 0.5) or fenugreek (DS Gal ¼ 0.9) are regarded are soluble in dilute and semi-dilute solutions and thermodynamically stable (neglecting possible hydro- lysis and bacterial degradation). Carob galactomannan (assumed as DS Gal ¼ 0.2–0.4) is generally regarded as partially soluble, and is reported to form weak gels after freeze–thaw treatment, in the presence of high concentra- tions of sucrose, or in ‘‘single-component’’ solutions when held near the freezing point of water (Richardson, Clark, Russell, Aymark, & Norton, 1999). This polysaccharide has additionally been studied intensively with respect to its role in altering the gel strength when mixed with ARTICLE IN PRESS www.elsevier.com/locate/foodhyd 0268-005X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2006.08.010 à Corresponding authors. Tel.: +41 44 632 8536; fax: +41 44 632 1155. E-mail addresses: pollardm@ilw.agrl.ethz.ch (M.A. Pollard), peter.fischer@ilw.agrl.ethz.ch (P. Fischer).