Emulsifying properties of sugar beet pectin microgels

Particle stabilized (‘Pickering’) oil-in-water (O/W) emulsions were fabricated using sugar beet pectin (SBP) microgel particles (SBPM) that differed in their crosslinking density and therefore elasticity. Droplet size distributions and emulsion microstructures were investigated via light scattering and complimentary imaging techniques: light microscopy, confocal laser scanning microscopy and scanning electron microscopy. Comparisons to emulsions stabilized by native (i.e., non-microgelled) SBP at equivalent overall SBP content were made throughout. The SBPM-stabilized emulsions (20 and 40 vol% oil) were shown to have an improved physical stability compared to those stabilized by SBP. For example, droplet coarsening on prolonged (9 week) storage at ambient temperature (25 °C) and on temperature cycling (75 °C) was substantially reduced for SBPM-stabilized emulsions. This is attributed to the greater steric barrier provided by SBPM particles and their higher energy of displacement. Furthermore, the higher viscoelasticity of the SBPM-stabilized emulsions (particularly at 40 vol% oil) retarded droplet creaming. This higher viscoelasticity could be due to weak flocculation of the SBPM-stabilized droplets or the strong influence of the SBPM on the viscoelasticity of the intervening aqueous phase, even at relatively low SBPM concentrations

Pectin-based microgels for rheological modification in the dilute to concentrated regimes

Hypothesis A novel range of microgel particles of different internal cross-linking densities can be created by covalently cross-linking sugar beet pectin (SBP) with the enzyme laccase and mechanically breaking down the subsequent parent hydrogels to sugar beet pectin microgels (SBPMG) via shearing. The bulk rheological properties of suspensions of the different SBPMG are expected to depend on the microgel morphology, elasticity (crosslinking density) and volume fraction respectively. Experiments The rheology of both dilute and concentrated dispersions of SBPMG were studied in detail via capillary viscometry and shear rheometry, supplemented by information on particle size and shape from static light scattering, confocal microscopy and electron microscopy. Findings For dilute suspensions of SBPMG, data for viscosity versus effective volume fraction (ɸeff) falls on a ‘master’ curve for all 3 types of SBPMG. In the more concentrated regime, the softer microgels allow greater packing and interpenetration and give lower viscosities at the same ɸeff, but all 3 types of microgel give much higher viscosities than the equivalent concentration of ‘non-microgelled’ pectin. The firmer microgels can be concentrated to achieve elasticities equivalent to the original parent hydrogel. All SBPMG suspensions were extremely shear thinning but showed virtually no time-dependence

Enzyme cross-linked Pectin Microgel Particles for Use in Foods

We report on a new enzyme-based method for producing permanently cross-linked pectin microgels. We investigate the shape, size and rheological properties of these microgel particles making comparisons with the more traditional design of calcium cross-linked pectin microgels. Both sets of microgel particles were prepared via the 'top-down' mechanical disruption of parent pectin hydrogels. The first hydrogel was prepared from low methoxyl pectin (LMP) (2 wt.% pectin) cross-linked using Ca2+ (8.3 mM CaCl2). The LMP microgels show particle sizes ca. 1 to 100 μm, but are stable only in [Ca2+] = 8.3 mM or above, swelling and/or dissolving rapidly in pure water. The second type of microgel was prepared from sugar beet pectin (SBP) hydrogels covalently cross-linked via laccase. Gelation kinetics were investigated by small amplitude oscillatory shear rheometry. The SBP microgels resisted dissolution in water for several months. Light scattering measurements suggested that the SBP microgel particle sizes were related to the mechanical properties of the parent hydrogels. Various imaging techniques all suggested that SBP microgels have highly irregular shapes, perhaps due to the top-down technique used for their manufacture and their inherent mechanical properties. Concentrating the SBP microgels (to 35 - 50 wt.% microgel, or 0.6 - 0.8 wt.% overall pectin concentration) resulted in suspensions with rheological properties typical of yield stress fluids. When compared at similar overall SBP concentrations, the SBP microgel suspensions offer distinct advantages as bulk rheology modifiers compared to SBP solutions