The emulsan polymer: Perspectives on a microbial capsule as an industrial product

Microbial polysaccharides have become significant industrial products in recent years, primarily because of their high molecular weight and unique rheological properties. More recently, a new class of microbial biopolymer has been developed—namely, the exopolysaccharide bioemulsifiers. The best studied of this class of biopolymer is the capsular anionic polysaccharide of the oil‐degrading bacterium Acinetobacter calcoaceticus RAG‐1, emulsan. The emulsan polymer (MW, 10⁶) consists of D‐galacatosamine, D‐galactosamine uronic acid (pK_a, 3.01), and a diamino deoxyhexosamine. The amphipathic properties of emulsan are due in part to the presence of fatty acids linked to the polysaccharide backbone in both ester and amide linkages. Emulsan is characterized by a very high affinity for the oil/water interface, and its major industrial application is in the stabilization of oil‐in‐water emulsions at very low concentrations (emulsan : oil, 1 : 1000). This interfacial binding is accompanied by a conformational change in the polymer, which in turn allows for the concentration of normally water‐soluble cations, proteins, and even phages in the oil layer after emulsion separation. Emulsan is now a commercial product produced by fermentation on an industrial scale. Two major applications are likely to involve its ability to stabilize heavy oil‐in‐water emulsions for (1) transportation in pipelines of high‐viscosity oils at lower temperatures and (2) upgrading of high‐viscosity fuels so that the homogeneous oil/water emulsions can be burned directly without water removal. Both applications have been tested on a semi‐industrial scale and their feasibility has been demonstrated.