Cereal Chem 66:90-93   |  VIEW ARTICLE

A Rheological Characterization of Cereal Starch-Glactomannan Mixtures.

M. Alloncle, J. Lefebvre, G. Llamas, and J. L. Doublier. Copyright 1989 by the American Association of Cereal Chemists, Inc. 

Wheat and corn starch dispersions with concentrations ranging between 1.5 and 7% were pasted in the presence of guar gum or locust bean gum. These mixtures were characterized by means of a coaxial cylinders viscometer. Flow curves of these starch-galactomannans mixtures were compared with the curves obtained from starch or galactomannan alone. A strong synergistic effect was observed, resulting in a dramatic increase in the viscosity of the mixtures compared with starch or galactomannan alone. A simple model is proposed to interpret such effects. Because starch pastes are described as suspensions of swollen particles dispersed in a macromolecular medium, it is suggested that galactomannans are located within the continuous phase. Thus, the volume of this phase, accessible to the galactomannan, is therefore reduced. This yields an increase of the galactomannan concentration within the continuous phase and a dramatic increase in the viscosity of the continuous medium owing to the thickening properties of this polysaccharide. Because the overall viscosity of a suspension depends upon the viscosity of the continuous phase as well as on the volume fraction of the dispersed phase, the respective contribution of each phase can be estimated. Validity of this model was supported by experiments where the galactomannan concentration in the continuous medium was kept constant (1%) while the volume fraction of the dispersed phase was varied between 0.1 and 0.9.