Surfactants are surface-active substances. All surfactants share a common chemical structure – a hydrophilic (water-loving) “head” and a hydrophobic (oil-loving) “tail”. Surfactants are generally classified into two groups: 1) Petroleum-derived or chemically synthesized surfactants and 2) Biologically produced biosurfactants. The primary functions of surfactants are to enhance cleaning efficiency, emulsification, wetting, dispersion, solubility, stabilization, foaming, defoaming, and lubricity of water-based compositions. These factors result in improved performance properties of water-based formulations including a range of ingredients such as other surfactants, solvents, thickeners, salts, chelating agents, foamers, defoamers and fragrances. Surfactants are sub classified by their ionic charge into four groups; anionic, nonionic, cationic and amphoteric surfactants. Anionic surfactants are the largest group and exhibit superior surfactant properties including wetting and emulsifying capacities.
Biosurfactants are any surfactant substances produced by living organisms. For example, rhamnolipids are biosurfactants that are made by a microbial fermentation. Most commonly used surfactants such as sodium lauryl sulfate (also sodium dodecyl sulfate or SDS) are synthetically produced and can cause skin irritation and environmental damage. However, biosurfactants are much less burdensome because they are readily biodegradable.
Rhamnolipids (RL) are members of the glycolipid biosurfactant family. Natural rhamnolipids of microbial origin are always produced as a mixture of various congeners or molecules with highly similar structures, functions and properties. An amphiphilic (water- and oil- loving) rhamnolipid molecule is composed of two moieties. One half is the water-loving sugar head having one or two rhamnose residues, and the oil-loving lipid tail possessing one or two fatty acid residues. The amphiphilic properties of rhamnolipids allow them to reduce interfacial tension between two substances that normally would not mix. When added to a mixture of two immiscible substances, such as water and oil, the rhamnolipids align themselves at the interface between the two substances. The rhamnose sugar moiety points towards the water while the fatty acid tail points towards the oil. When the substances are mixed the rhamnolipids allow an emulsion to form. The structural diversity of rhamnolipids is determined by the number of rhamnose (one/mono or two/di) and fatty acid (one or two) residues, and the fatty acid composition. The length of the constituent fatty acids and their combinations are largely variable, though mono-rhamnolipid Rha- C10-C10 and di-rhamnolipid Rha-Rha- C10-C10 are typically found to be the dominant components in a naturally produced mixture. Rhamnolipids are the most extensively studied, widely applicable and environmentally friendly biosurfactants, with an excellent human safety profile. Rhamnolipids may be manufactured in a variety of forms such as solid/granular, powder, paste-like/honey-like/syrup-like/wax-like and aqueous solutions.