Emulsification properties of hydrocolloids

Water soluble/dispersible polysaccharides, termed hydrocolloids or gums, are known as viscosity builders and/or gelling agents in aqueous systems. Technologists call them stabilizers, since they can improve long-term stability in systems consisting of water and oil. Many scientists claim that hydrocolloids are not true emulsifiers, since they do not actively adsorb onto liquid interfaces and the stability that they impart is mainly via increasing viscosity and decreasing mobility. Only certain hydrocolloids, such as gum arabic, were known to exhibit emulsification properties. The surface activity was proved to be derived from the anchoring ability of the hydrophobic proteineous moieties (attached to the polysaccharide backbone) onto the oil phase. The aim of this review is to demonstrate that certain hydrophilic (anionic or non-ionic) polysaccharides purified to a level of being almost protein-free can exhibit surface and emulsification properties inspite of their rigid and hydrophilic nature. The adsorption isotherms of the surface-active biopolymers are similar to other macromolecular amphiphiles. The main gums to be discussed are those of the galactomannan family [locust bean gum (LBG), guar and fenugreek]. Other gums from less known sources (Portulaca Oleracea and Opuntia Ficus) also exhibit surface properties. It appears that the statements made by several authors claiming that hydrocolloids cannot be considered as emulsifiers, were inaccurate. It seems that the requirements for built-in hydrophobic moieties on the hydrocolloids' backbone internal structure, are not obligatory for active adsorption. Adsorption can be induced by a salting-out effect, resulting in semi-solid interfacial layers. Hydrocolloids can form thick birefringent gel-like mechanical barriers at the oil-water interface of emulsion oil droplets. This new category of natural-occurring hydrocolloid-emulsifiers should be reconsidered by food technologists and by other emulsion technologists for other industrial applications.