Structure and Properties of Biosurfactants

This chapter describes the isolation, structure elucidation, and properties of some bacterial, yeast, and fungal biosurfactants. With regard to the isolation of glycolipids from microbial cultures, generally it is to distinguish between cell wall-bound and extracellular compounds. The subsequent purification procedure includes adsorption column chromatography on silicic acid, thick-layer chromatography on silica gel, and often a crystallization. In the structure elucidation studies, the glycolipids showed normal sensitivity to alkaline or acidic hydrolysis: the ester linkages were broken by saponification, the O-glycosidic bonds were split by acidic conditions. The higher the molecular weight the more difficult is it to elucidate the structure of biosurfactants; in the case of proteinic activators or emulsifiers only the amino acids and carbohydrate moieties were analyzed after hydrolysis. The following compounds belong to the bacterial surfactants: rhamnose lipids, trehalose lipids, different mono-, di-, and trisaccharide lipids, amino acid-containing lipids, peptidolipids and hydrophobic proteins.