Swelling of high acyl gellan gum hydrogel: Characterization of network strengthening and slower release.

This study examined the mechanism of swelling for high acyl (HA) gellan gum and the impacts on the hydrogel mechanical properties and the release of a model drug (glucose). Controlling the material properties and the release of entrapped drugs during use in aqueous environments, such as the stomach or bodily fluids, are crucial in designing functional applications. Swelling of HA gellan gum was controlled by varying the osmotic environment with salts and solvents, and effects on the gel network were characterized by uniaxial compression tests, DSC, and rheology. Low ionic strength solutions caused the greatest degree of swelling (up to 400 %) and corresponded to a more brittle gel with a greater modulus and greater network enthalpy. Swelling slowed the release of glucose by decreasing the diffusion flux. The osmotic environment was found to produce different functional properties, and it is crucial to consider these changes in the design of formulations.

The hydrophobic modification of kappa carrageenan microgel particles for the stabilisation of foams.

HYPOTHESIS: Polysaccharides such as kappa carrageenan are often utilised in fat replacement techniques in the food industry. However, the structural role they can provide within a product is limited by their hydrophilic nature. Hydrophilic particles can be surface-activated by hydrophobic modification e.g. in-situ interaction with a surfactant. This can drastically improve foam stability by providing a structural barrier around bubble interfaces offering protection against disproportionation and coalescence. Hence, it should be possible to bind negatively charged kappa carrageenan particles with a cationic surfactant through electrostatic interaction, in order to alter their surface properties. EXPERIMENTS: Lauric arginate was mixed with kappa carrageenan microgel particles at various concentrations and the potential electrostatic interaction was studied using zeta potential, turbidity and rheological measurements. Mixtures were then aerated and foaming properties explored, in particular the location of the particles. FINDINGS: Lauric arginate was successfully bound to kappa carrageenan microgel particles. Consequently, particles were surface-activated and adsorbed at the air/water interface, as shown by optical and confocal microscopy. Foam half-life peaked at an intermediate surfactant concentration, where there was sufficient surfactant to coat particle surfaces but the concentration was low enough to prevent the formation of large aggregates unable to adsorb at the a/w interfaces.

Temperature influences on network formation of low DE maltodextrin gels.

Gelation of maltodextrin (DE 2) was examined over a range of temperatures to understand the behaviour within mixed-gel systems. Maltodextrin solutions were prepared at 95 °C and held at temperatures between 5 °C and 60 °C for four days. Bulk gel properties and the underlying microstructure were analysed using fracture strength, proton relaxation time, and differential scanning calorimetry (DSC). Holding at lower temperatures led to a greater gel strength with a brittle and crumbly texture. Analysis of the microstructure showed that gelation at 10 °C versus 60 °C produced a greater number of aggregates (melting enthalpy 14.5 J/g versus 3.4 J/g) and structuring of a higher melting entropy (45 mJ/g K versus 10 mJ/g K). A thermal hysteresis with signs of structure corresponding to both holding temperatures was also measured. Elevated temperature was hypothesized to decrease the amount of smaller molecular weight chains participating in aggregation by shifting from the helix to coil form.