A review on microbial surfactants: production, classifications, properties and characterisation

Surfactants are a surface-active group of molecular compounds with hydrophobic and hydrophilic moieties in one single molecule that distributes themselves between two immiscible fluids, reduce surface/ interfacial tensions and cause the solubility of non-polar compounds in polar solvents. Besides surface and interfacial activities, they display properties such as solubilization, detergency, lubrication, emulsification, stabilization and foaming capacity. Microbiologically derived surfactants are called biosurfactants. They are produced as either metabolic products or as the surface chemistry of an actual cell. The employment of screening techniques such as surface tension measurements, drop collapse test, oil spreading assay, emulsification index (%EI₂₄), CTAB/methylene blue agar plate test and strain characterization. Others are analytical techniques including liquid chromatography-mass spectroscopy, thin layer chromatography, high-performance liquid chromatography, Fourier transform infrared spectroscopy, nuclear magnetic resonance, fast atom bombardment-mass spectrometry and electrospray ionization-mass spectrometry. These had led to the identification of biosurfactant producing microorganisms, properties and characterization of biosurfactants. Therefore, this review tends to provide the current knowledge of the screening techniques and chromatography/spectroscopic tools employed to study biosurfactants. Results from a detailed study of these tools can unveil new surfactant producing microorganism, decipher chemical diversity and multifunctional properties of biosurfactants critical for applications in diverse industrial sectors.