Design and rheological performance of microgel suspensions and microgel stabilised emulsions

This thesis describes the fabrication, characterization and applications of pectin based microgels. A variety of techniques commonly used to characterize colloidal and soft matter systems (i.e., particle size analysis, microscopy techniques and shear
rheometry) were used throughout.

Microgel suspensions were prepared in large quantities using a simple and scalable ‘top-down’ technique. This involved the fabrication of crosslinked ‘parent’ pectin hydrogels which were subsequently combined with a suitable solvent and subjected to mechanical disruption to yield microgel suspensions. Such systems are promising candidates as novel food additives for purposes of rheology modification and emulsification.

It was shown that the rheological properties (viscosity and elasticity) of microgel suspensions can be tailored by varying the elasticity and effective volume fraction of microgel particles. The former is easily controlled via the elasticity of parent hydrogels, which in turn depends on the crosslinking density. The use of microgel suspensions as rheology modifiers is shown to provide distinct benefits over native polymer solutions and crosslinked polymer gels respectively. The ability to engineer desirable flow behaviour is likely to be a significant advantage to the manufacturerwhen developing new products or processes.

Converting pectin to pectin microgels also improved their functional properties when such systems were used as stabilizers of oil-in-water emulsions. Microgel stabilized emulsions were more resistant against droplet coarsening on prolonged storage and when subjected to temperature cycling as compared to native pectin stabilized emulsions. Furthermore, the particulate nature of the microgels resulted in emulsions with enhanced rheological properties at the same overall biopolymer concentration.