Starch stabilized Pickering emulsions : Colloidal starch particles and their effects on emulsion properties

Sammanfattning: Particles can be used to stabilize multi-phase systems known as Pickering emulsions. The aim of this thesis was to investigate how starch particles affect emulsion properties. Starch granules were used individually as well as in binary mixtures. To obtain a wide variety of starch properties granules were selected based on botanic variation (quinoa, oat, waxy barley, waxy maize and potato). The properties of the starch particles were furthermore changed by size fractionation by sedimentation, acid hydrolysis, cold gelatinization, or dissolution-precipitation, which resulted in different particle sizes and shapes. Almost all samples were modified with octenyl succinic anhydride (OSA) to 1.7%-3%. The particle size was found to be important, since decreased particle sizes lead to decreasing emulsion drop size and increased stabilization against creaming. Decreased particle size up to 89% (potato), 64% (waxy maize) and 62% (waxy barley) by acid hydrolysis, and from 15µm to 120nm (waxy maize) by dissolution-precipitation, had a strong impact on decreasing emulsion drop size. The shape also influenced the affinity for the oil/water interface. Smooth rounded particles (waxy barley <10µm) seemed to provide smaller emulsion drops than smaller/similar sizes of polyhedral particles (quinoa and oat). Starch particles from ~120nm (nanoparticles) to <10µm (granules) were suitable for stabilization of emulsions, and the smaller the particle, the lesser weight of starch was needed for droplets stabilization. The best emulsifying capacity and stability was obtained with the nanoparticles (~120nm particle size) which gave emulsions that were stable for up to 1 year. Mixtures of starch granules in emulsion systems showed that when two types of starch granules are mixed, one is more likely to dominate on the interface but when the starch content is low both starches might adsorb. In the case of oat starch, it was seen that Pickering emulsion could be formed also with granules that had not been OSA-modified and that these adsorbed granules could be gelatinized in situ using CaCl2. Cold gelatinization of oat resulted in an increase in particle size and at a minimum level of gelatinization these swelled granules increased the emulsion index for the emulsions they were stabilizing. The work in this thesis shows the potential and versatility of starch granules and its derivatives as emulsifiers.