Stabilisation of emulsions using hydrophobically modified inulin (polyfructose)

Oil-in-water (O/W) emulsions were prepared using a hydrophobically modified inulin surfactant, INUTEC®SP1. The quality of the emulsions was evaluated using optical microscopy. Emulsions, prepared using INUTEC®SP1 alone had large droplets, but this could be significantly reduced by addition of a cosurfactant to the oil phase, namely Span 20. The stability of the emulsions was investigated in water, in 0.5, 1.0 and 2 mol dm−3 NaCl as well as 0.5, 1.0, 1.5 and 2 mol dm−3 MgSO4. All emulsions containing NaCl did not show any strong flocculation or coalescence up to 50 °C for almost 1 year storage. With MgSO4 they were stable up to 50 °C and 1 mol dm−3. The stability of the emulsions against strong flocculation and coalescence could be attributed to the conformation of the polymeric surfactant at the O/W interface (multipoint attachment with several loops) and the strong hydration of the polyfructose chain in such high electrolyte concentrations. This was confirmed using cloud point measurements, which showed absence of any cloudiness up to 100 °C and at NaCl concentrations reaching 4 mol dm−3 and MgSO4 reaching 1 mol dm−3. These high cloud points in electrolyte solutions could not be reached with polyethylene glycol. This clearly demonstrated the superiority of INUTEC®SP1 surfactant as an emulsion stabiliser when compared with surfactants based on polyethylene glycol. Viscoelastic measurements showed a gradual increase in the storage modulus G′ with storage time both at room temperature and 50 °C. This was indicative of weak flocculation and absence of coalescence. The weak flocculation of the emulsions could be attributed to the presence of an energy minimum, Gmin, in the energy–distance curve.