ELSEVIER Food Hydrocolloids12 (1998) 43-53 FOOD HYDROCOLLOIDS Flocculation of food dispersions by gums" isotropic/anisotropic dispersion separation by xanthan gum Kalman Koczo al, Darsh T. Wasan a*, Rajendra R Borwankar b, Alex Gonsalves b aIllinois Institute of Technology, Chemical Engineering Department, Chicago, IL 60616, USA bKrafl Foods, Glenvie~, IL 60025, USA Received24 October 1996; accepted 16 January 1997 Abstract Creaming (flocculation) of a model food dispersion in the presence of xanthan and guar gums was studied using phase separation measurements, back-light scattering studies and microscopic observations. Xanthan gum was a much more effective flocculent than guar gum, especially at lower gum concentrations. Dispersion separation with xanthan gum also showed interesting features. The degree of separation gradually decreased with decreasing xanthan gum concentration and creaming could be detected as low as 10 ppm xanthan. Moreover, separation by xanthan gum was non-specific on the nature of the dispersion (fat, silica or latex dispersion) and had a phase separation character: most of the macromolecules migrated out of the flocculated dispersion into the aqueous phase. Based on these observations, it is suggested that the mechanism of dispersion separation by xanthan gum is a geometrical incompatibility between the anisotropic, worm-shaped xanthan molecules and the isotropic dispersed particles. The effects of xanthan gum molecular mass and dispersion concentration were in agreement with the theories on isotropic/anisotropic phase separations. © 1998 Published by Elsevier Science Ltd. All rights reserved. 1. Introduction Gums and other macromoleeules are frequently used to control the texture and structure of food or other oil-in- water emulsions and dispersions. Another function of these macromolecule additives is to prevent the dispersed drops or particles from settling or creaming due to the increased viscosity and yield stress. In several cases, however, the macromolecules, instead of stabilizing, rather flocculate, aggregating the dispersed drops or particles. Many investig- ators have studied the mechanism of dispersion flocculation by macromolecules and generally two basic mechanisms are mentioned: bridging and depletion (Napper, 1983). Bridging flocculation can occur if the macromolecules adsorb on the dispersed particles. If the macromolecules adsorb on two or more particles they anchor and aggregate those particles. This can happen at low macromolecule concentrations, typically at the level of a few ppm. At higher polymer concentrations the probability that a macro- molecule adsorbs to more than one particle is small and the *Correspondingauthor. lpresent address: WITCOCorp., OSi SpecialtiesGroup, 777 Old Saw Mill River Rd, Tarrytown, NY 10591, USA. polymers form a protecting adsorption layer on the particles, thus stabilizing them. Depletion flocculation occurs with non-adsorbing macromolecules when the distance between the dispersed particles is smaller than the size of the macromolecules, In this case the macromolecules get depleted from between the particles; the osmotic pressure between the particles is therefore lower than the pressure around them and the solvent starts to flow out from between the particles, pushing them together. Gums are frequently used macromolecular food additives. The addition of these hydrocolloids strongly increases emulsion viscosity, even at low concentrations, especially with some gum mixtures, such as the mixture of xanthan and guar gums. It is generally claimed (BeMiller, 1980) that gums are dispersion stabilizers. However, several authors have recently studied the effect of gums on dispersion stability and found that the addition of gum results in dispersion flocculation. Gunning et al. (1988a,b) investigated the creaming of oil-in-water emulsions induced by xanthan gum at relatively high xanthan concentrations (0.1-0.33%). Cao et al. (1990, 1991) studied the floccula- tion of hydrocarbon oil-in-water emulsions stabilized by sodium caseinate in the presence of various polysac- charides, including xanthan gum, and found a general 0268-005X/98/$19.00 + 0.00. © 1998 Published by Elsevier Science Ltd. All rights reserved.