HYDROCOLLOIDS AS FOOD EMULSIFIERS AND STABILIZERS

Hydrocolloids are water-soluble biopolymers consisting of high molecul ar weight polysaccharides known as viscosity builders, gelification ag ents and stabilizers of food systems. Several hydrocolloids such as gu m arabic (acacia), tragacanth, xanthan and certain modified gums have been mentioned as food additives having special functions such as: ''r etardation of precipitation of dispersed solid particles and coalescen ce of oil droplets''. The role of these gums as emulsifiers remained s omewhat obscure. The present review is an attempt to bring the relevan t studies together and to throw some light on the functionalities of t he gums as surface active agents and food emulsifiers. In addition, so me recent results obtained in our laboratory are discussed. Gum arabic is compared to colloidal microcrystalline-cellulose (MCC) and galacto mannans (recent results) in view of their ability to reduce surface te nsions, interfacial tensions and to stabilize oil in water emulsions v ia the 'steric' and 'mechanical' stabilization mechanisms. It is demon strated that while gum arabic adsorbs strongly and effectively onto th e oil droplets via its proteinaceous moieties, guar gum and locust bea n gum (LBG) adsorb weakly and for the most part only ''precipitate'' o n the oil surface, and form birefringent layers of the polymer oriente d with its hydrophobic mannose backbone facing the oil. The stabilizat ion with MCC is claimed to be achieved via adsorption of solid particl es on the oil droplets (mechanical stabilization).