Starch Pickering Emulsions : Process and Encapsulation Stability
Abstract: The emulsion stabilization functionality of surfactants and biopolymers can be replaced by solid particles adsorbed at the interface, where they create a category of emulsions known as Pickering emulsions. Recently, health and environmental concerns have led to new market demand for natural, biodegradable and renewable sources of ingredients. Starch granules meet these ingredient requirements and are also good candidates for stabilization of Pickering type emulsions due to their properties such as neutral color, taste, odor and being non-allergic. Starch granules are generally hydrophilic and in order to improve their emulsifying capacity they are modified with hydrophobic groups. The most widely used chemical modification is esterification with acid anhydride, such as octenyl succinic anhydride (OSA). Emulsions stabilized by OSA modified starch have shown to have high stability. Moreover, the application of a heat treatment can induce a partial gelatinization of the starch at the oil-water interface, which leads to changes in interfacial properties of the starch granule stabilized emulsions. This thesis focuses on the development and application of starch Pickering emulsions and has been carried out along three main lines of investigation where each line has its own section in the thesis. In the first section, the preparation and properties of oil-in-water emulsions stabilized by starch granules with small sizes, including quinoa, rice and amaranth, were investigated. In the second section, the process and encapsulation stabilities of the emulsions were evaluated in the context of simple oil-in-water and double water-in-oil-in-water emulsions, with or without heat treatment. In the third section, the physical and encapsulation stabilities of the emulsions during in vitro digestion were evaluated. Quinoa starch granules showed to have higher emulsifying efficiency both in the initial state and after accelerated stability testing. Moreover, the heat induced gelatinized layer showed to not only contribute to initial general stability, but also increased the process and encapsulation stabilities of the emulsions. Modified starch granules appeared to protect the emulsions against destabilization mechanisms during processing (i.e. freezing and freeze-drying). It was possible to create powders from starch stabilized Pickering emulsions with high oil content (up to 80%). Furthermore, emulsions stabilized by starch granules showed high stability for encapsulation of bioactive compounds during in vitro digestion. The results of this work can be used for the development of lipid-based encapsulated systems, in both liquid and powder forms for the delivery of bioactive compounds in food, pharmaceutical and cosmetic applications.
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