Biosurfactants and Bioemulsifiers Biomedical and Related Applications – Present Status and Future Potentials

Many microorganisms are able to produce a wide range of amphipathic compounds, with both hydrophilic and hydrophobic moieties present within the same molecule which allow them to exhibit surface activities at interfaces and are generally called biosurfactants or bioemulsifiers. These surface-active compounds (SAC) are mainly classified according to their mode of action, molecular weight and general physico-chemical properties. In literature, the terms ‘biosurfactants’ and ‘bioemulsifiers’ are often used interchangeably, however in general those that reduce surface and interfacial tension at gas-liquid-solid interfaces are called biosurfactants and those that mainly reduce the interfacial tension between immiscible liquids or at the solid-liquid interfaces leading to the formation of more stable emulsions are called bioemulsifiers or bioemulsans. The former group includes lowmolecular-weight compounds, such as lipopeptides, glycolipids, proteins, while the latter includes high-molecular-weight polymers of polysaccharides, lipopolysaccharides proteins or lipoproteins (Smyth et al., 2010a, 2010c). In heterogeneous systems, biosurfactants tend to aggregate at the phase boundaries or interfaces. They form a molecular interfacial film that affects the properties (surface energy and wettability) of the original surface. This molecular layer, in addition to lowering the surface tension in liquids, also lowers the interfacial tension between different liquid phases on the interfacial boundary existing between immiscible phases and therefore can have an impact on the interfacial rheological behaviour and mass transfer. When at interfaces (solidliquid, liquid-liquid or vapour-liquid), the hydrophobic moiety of the surface active molecules aggregates at the surface facing the hydrophobic phase (usually the oil phase) while the hydrophilic moiety is oriented towards the solution or hydrophilic phase (mainly water). Their diverse functional properties namely, emulsification, wetting,