Structure-emulsifying activity relationship of a biosurfactant emulsan and characterization of a novel lipopolysaccharide biosurfactant

Abstract

To investigate the relationship between the structure and the emulsifying activity of a lipopolysaccharide biosurfactant, emulsan from Acinetobacter calcoaceticus RAG-1, the emulsan samples having various structure were prepared such as different fatty acid contents and composition, and different carbohydrate backbone structure under different culture conditions such as kind of carbon source, temperature, growth stage, specific growth rate, inhibition of fatty acid biosynthesis, and combination of above conditions, and the structure of the purified emulsan samples were determined using GC and GC-MS. The fatty acid, only hydrophobic moiety of emulsan, partially influenced the emulsifying activity. The emulsifying activity was proportional to the fatty acid contents until 8%, and then reached plateau above 8%. The composition of fatty acid did not play an important role in their emulsification. Effect of protein moiety of emulsan was confirmed by comparing the emulsifying activity after removal of protein by hot-phenol method, and no effect was found on the emulsification. In the study of carbohydrate backbone structure, emulsan was found to have a branched-structure rather than linear structure. The emulsifying activity of emulsan was proportionally increased as the branching degree of polysaccharide backbone increased. To decide the more important structural factor influencing the emulsifying activity, statistical analysis was performed by the fatty acid content and the branching degree of polysaccharide. It was concluded that the emulsifying activity of emulsan was more influenced by the branching degree rather than the fatty acid contents. It was, thus, suggested that the oil droplet could be more efficiently surrounded by highly branched polysaccharide backbone oil/water in emulsion system, resulting in the formation of more stable emulsion.

A novel biosurfactant producing strain was isolated and identified to Klebsiella oxitoca BSF-1 from Korean soil. The...