Structural and physicochemical characterization of a rhamnolipid biosurfactant

Rhamnolipids are an important class of biosurfactants having many uses in pharmaceutical, agricultural, food, cosmetics, and detergent industries. The present study used various analytical techniques to characterize the biosurfactant produced by Achromobacter xylosoxidans PSA5. The characteristic absorption bands in FT-IR spectroscopy also revealed its glycolipid nature. NMR spectroscopy, in conjunction with the LC-MS analysis, identified the chemical structure of the biosurfactant as a di-rhamnolipid. The surface tension of water was lowered to 25.19 mN/m, and the rhamnolipid showed a critical micelle concentration of 174.375 mg/L. The highest emulsification index of 69.69% was observed against engine oil. Further, the activity of the biosurfactant was stable across a broad pH range (2-10), temperature (30-100°C), and salt concentrations (2, 4, 6, 8, and 10%). The surface-active properties and the stability of these biomolecules suggest their potential use in bioremediation, and the petroleum industry, particularly in extreme conditions.