Studies on Emulsification Properties of Glycolipids Biosurfactants

Abstract

Microbial biosurfactants consists of hydrophilic and hydrophobic moieties in its structure and are produced by microorganisms. Glycolipid class of biosurfactants has wide range of surface and interfacial properties. The emulsification activity and emulsion stability of the Glycolipids Trehalose lipids (THL), Mannosylerrythritol lipids (MEL), Sophorolipids (SL) and Rhamnolipids (RL) were investigated using liquid paraffin (hydrocarbon source) and sunflower oil (vegetable source) as hydrophobic source by UV spectroscopy. Emulsification activity and stability are in the order THL > MEL > SL > RL. The stability as a function of the temperature in the range of 20 °C – 80 °C is in order THL > SL > MEL > RL. The effect of pH was studied using buffers of acidic and basic pH. It was observed that RL and SL had excellent emulsification activity at pH 8 while the activity of trehalose lipids and mannosylerrythritol lipids was not affected by pH. Similar effect of various concentrations of salt (NaCl) was studied; THL and MEL emulsion were very resistant to concentration of salt but the stability of SL and RL emulsion decreased with increased salt concentration. Average droplet diameter of emulsion and the polydispersity index were determined by dynamic light scattering. The emulsions of THL and SL have smallest droplet diameter of 422 nm and 625 nm, while emulsions of MEL and RL have a droplet size of 1923 nm and 2245 nm respectively. Emulsions of all investigatesd glycolipid surfactants had good polydispersity index and negative zeta potential, suggesting their possible applications in pharmaceutical, cosmetics, industrial and environmental techniques.