Emulsan is an extracellular polyanionic lipopolysaccharide produced by Gram-negative hydrocarbon-degrading bacterium, Acinetobacter calcoaceticus RAG-1. Emulsan contains about 15% long fatty acid esters which are thought to modulate hydrophilic-lipophilic balance. It was found that the composition of fatty acid esters of emulsan could be significantly altered by supplying the different types of chemicals as a carbon and energy source in the culture medium. Emulsan having the modified fatty acid group also showed the different emulsifying activity in hydrocarbon-in-water system. Emulsan contained at least 10 different fatty acids and major components were found to be 3-hydroxydodecanoic acid, hexadecanoic acid, and octa decenoic acid. Among them, 3-hydroxydodecanoic acid seems to be the most important fatty acid in the active emulsan preparations. Molecular weight of emulsan samples produced from different carbon sources was in the range of 9.0×$10^6$-1.4×$10^7$ and there was no corelation between emulsifying activity and molecular weight of emulsan with different fatty acid composition. Emulsan did not appreciably reduce surface and interfacial tension, but it was a very effective emulsifying agent for hydrocarbons in water even at a content as low as 0.0013%-0.013%. It implies that emulsan is a good emulsifier rather than a good surfactant. Emulsan effectively protected oil-in-water emulsions from coalescence and give the enhanced stability.
