Self-assembly and emulsification properties of hydrophobically modified inulin

A series of alkenylated inulin samples were synthesized in aqueous solution using alkenyl succinic anhydrides with varying alkenyl chain lengths (C8-C18). The inulin derivatives (ASA-inulins) were characterized using NMR and FTIR and their degree of substitution determined. The solution properties of ASA-inulins were investigated using dye solubilization, surface tension, and dynamic light scattering, and all three techniques confirmed that the molecules aggregated in solution above a critical concentration (critical aggregation concentration, CAC). The value of the CAC was found to be reasonably consistent between the different techniques and was shown to decrease with increasing alkenyl chain length, from 0.08% for the octenyl succinylated sample to 0.005% for the octadecenyl succinylated sample. The hydrodynamic diameter of ASA-inulins above the CAC was determined from dynamic light scattering studies and was shown to increase with alkenyl chain length, from 4 nm for the octenyl derivative to 55 nm for the hexadecenyl derivative. All ASA-inulins were shown to be able to produce oil-in-water emulsions with a droplet size similar to that of emulsions prepared using Tween 20 on storing for 21 days. The fact that the derivatives are able to form micellarlike aggregates and stabilize emulsions makes them suitable candidates for the encapsulation and delivery of water-insoluble active compounds, with potential application in food, cosmetic, personal care, and pharmaceutical formulations.