title: Water adsorption isotherms of carboxymethyl cellulose, guar, locust bean, tragacanth and xanthan gums.
abstract: Water adsorption isotherms of carboxymethyl cellulose (CMC), guar gum (GG), locust bean gum (LBG), tragacanth gum (TG) and xanthan gum (XG) were determined at different temperatures (20, 35, 50, and 65°C) using a gravimetric method. Several saturated salt solutions were selected to obtain different water activities in the range from 0.09 to 0.91. Water adsorption isotherms of tested hydrocolloids were classified like type II isotherms. In all cases, equilibrium moisture content decreased with increasing temperature at each water activity value. Three-parameter Guggenheim-Anderson-de Boer (GAB) model was employed to fit the experimental data in the water activity range and statistical analysis indicated that this model gave satisfactory results. CMC and GG were the most and the least hygroscopic gums, respectively. Sorption heats decreased with increasing moisture content. Monolayer moisture content evaluated with GAB model was consistent with equilibrium conditions of maximum stability calculated from thermodynamic analysis of net integral entropy. Values of equilibrium relative humidity at 20°C are proposed to storage adequately the tested gums.
authors.affiliation: Departamento de Enxeñaría Química, Escola Técnica Superior de Enxeñaría, Universidade de Santiago de Compostela, Campus Vida, 15782 Santiago de Compostela, Spain.
authors.forename: María D
authors.initials: MD
authors.lastname: Torres
authors.affiliation: Departamento de Enxeñaría Química, Escola Técnica Superior de Enxeñaría, Universidade de Santiago de Compostela, Campus Vida, 15782 Santiago de Compostela, Spain.
authors.forename: Ramón
authors.initials: R
authors.lastname: Moreira
authors.affiliation: Departamento de Enxeñaría Química, Escola Técnica Superior de Enxeñaría, Universidade de Santiago de Compostela, Campus Vida, 15782 Santiago de Compostela, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Chenlo
authors.affiliation: Departamento de Enxeñaría Química, Facultade de Ciencias, Universidade de Santiago de Compostela, Campus Lugo, 27002 Lugo, Spain.
authors.forename: María J
authors.initials: MJ
authors.lastname: Vázquez
mesh_terms: D000327:Adsorption; D002266:Carboxymethylcellulose Sodium / Q000737:chemistry*; D005685:Galactans / Q000737:chemistry*; D008351:Mannans / Q000737:chemistry*; D008962:Models, Theoretical; D053149:Plant Gums / Q000737:chemistry*; D011135:Polysaccharides, Bacterial / Q000737:chemistry*; D013816:Thermodynamics; D014144:Tragacanth / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D005685:Galactans; D008351:Mannans; D053149:Plant Gums; D011135:Polysaccharides, Bacterial; D014867:Water; D014144:Tragacanth; C007894:guar gum; D002266:Carboxymethylcellulose Sodium; C002563:xanthan gum; C017471:locust bean gum