Polymer or microgel particle: Differences in emulsifying properties of pectin as microgel or as individual polymer chains

The differences and similarities in the emulsion stabilising behaviour of pectin as individual polymer chains or as pectin-based microgels (particulate polymer network) were investigated. To compare the emulsifying properties and the adsorption mechanism, oil-in-water emulsions were produced with either pectin as individual polymer chains or as pectin-based microgels. The droplet size distribution of polymer stabilised emulsions varied depending on the used pectin type (apple and citrus pectin or pectinic acid). However, when microgel particles were used, the droplet size distribution remained constant, regardless of the pectin type. Further investigations were conducted with pectinic acid, due to comparable emulsification results when used as individual polymer chains or as microgel particle. Interfacial tension measurements revealed that microgel particles made from pectinic acid do not affect the oil-water interfacial tension, whereas pectinic acid as individual polymer chains decreases its value. This shows that microgels prepared with pectinic acid stabilise emulsions with a completely different mechanism than pectinic acid as individual polymer chains. The effect of the homogenising pressure difference on the droplet size distribution was investigated to gain further insight into the stabilizing mechanism. Emulsions stabilised with pectinic acid as individual polymer chains showed increased coalescence with increasing pressure difference, whilst emulsions stabilised with pectinic acid as microgel particles were not affected by an increase in the pressure difference. The gained knowledge can help to choose suitable process and formulation parameters for applications in which pectin is used as an emulsifier, whether as an individual polymer chain or as a microgel particle. For example, when high homogenisation pressure differences are required, microgel particles are more suitable than pectin as individual polymer chains, due to the low oil droplet coalescence. On the other hand, when high concentrations of emulsifying agent is required, pectin as individual polymer is the more appropriate choice.