Emulsifying properties and structure characteristics of octenyl succinic anhydride-modified pullulans with different degree of substitution.

Pullulan was successfully esterified with octenyl succinic anhydride (OSA) in aqueous alkaline solutions. The degree of substitution (DS) was regulated from 0.0163, 0.0346 to 0.0469 by changing the OSA concentration (3.0%, 6.0% and 9.0%, respectively). Meanwhile, the weight-average molecular weight (M) of OSA-pullulans varied from 2.050 × 10, 2.113 × 10 to 2.124 × 10. The chemical structures of OSA-pullulans were characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance spectroscopy (H NMR), which indicated that OSA groups were successfully grafted into pullulan. The surface tension, interfacial tension and droplet size of the emulsions stabilized by OSA-pullulans significantly reduced with the increase of DS. Furthermore, the emulsion stability (ES) and viscosity dramatically increased with DS compared with those of emulsion stabilized by pullulan. These results indicated emulsifying properties of OSA-pullulans were improved by increasing DS. Additionally, OSA-pullulans had excellent emulsion stability when DS was higher than 0.0346.