They reduce the free energy of the system by replacing the bulk molecules of higher energy at an interface. By reducing the interfacial tension and forming micelles, surfactants or biosurfactants have shown many environmental applications including enhanced oil recovery, removal of heavy metals from contaminated soil and remediation of hydrophobic organic compounds from soil [2–4]. They are used in environmental applications to enhance solubility of organic or inorganic components for soil washing or flushing. Typical desirable properties include solubility enhancement, surface tension reduction and low critical micelle concentrations (CMC).
Yeast and bacteria can produce biosurfactants, biological surfactants from various substrates including sugars, oils, alkanes and wastes [5]. Some types of biosurfactants are glycolipids, lipopeptides, phospholipids, fatty acids, neutral lipids, polymeric and particulate compounds [6]. Most are either anionic or neutral, while only a few with amine groups are cationic. The hydrophobic part of the molecule is based on long-chain fatty acids, hydroxy fatty acids or α-alkyl-β-hydroxy fatty acids. The hydrophilic portion can be a carbohydrate, amino acid, cyclic peptide, phosphate, carboxylic acid or alcohol.
