Hydrophobically modified chitosan microgels stabilize high internal phase emulsions with high compliance.

Food-grade microgel-stabilized emulsions have been attracting much attention due to their promising applications in food formulations. In this study, the use of hydrophobically modified chitosan microgels (h-CSMs) as particle emulsifiers to stabilize high internal phase emulsions (HIPEs) was demonstrated for the first time. Four hydrophobically modified chitosan (h-CS) were obtained by grafting deoxycholic acid (DA) with chitosan (CS) at grafting rates of 4.64%, 13.21%, 15.12% and 30.29%, respectively. The selected modified chitosan were further cross-linked with sodium tripolyphosphate (TPP) to form h-CSMs. It was found that, compared to pure CS and the modified h-CS, the h-CSMs have higher hydrophobicity, and can stabilize oil-in-water HIPEs effectively. The interfacial properties of the h-CSMs, and the formation, microstructure and rheological properties of HIPEs were characterized by dynamic interfacial adsorption, contact angle, visual observation, laser confocal microscopy and rheological measurements, respectively. The results show that stable HIPEs with oil concentration up to 90 wt% can be formed using very low h-CSM particle concentration (only 0.05 wt% for the HIPE with 90 wt% oil), and the HIPEs stabilized by h-CSMs displayed higher rheological compliance than other solid particle stabilized HIPEs at high oil volume fraction. The strong emulsification properties of the h-CSMs are attributed to their increased hydrophobicity, the enhanced exposure of hydrophobic groups during microgelation process, and the viscoelasticity of h-CSMs.