Modified starch granules as particle-stabilizers of oil-in-water emulsions

Oil-in-water (O/W) emulsions of 20 vol% n-tetradecane have been prepared using food-compatible hydrophobic starch particulates as the primary emulsifier. As such, the systems appear to be Pickering emulsions. The starch particulates were generated from chemically cross-linked granules that do not swell on prolonged contact with water and which were made partially hydrophobic by reaction with octenyl succinic anhydride. The degree of substitution was of the order of 0.03. The size of the modified starch particulates was reduced by freezer-milling before preparing the emulsions via a jet homogenizer. Conventional light transmission microscopy, confocal laser scanning microscopy, scanning electron microscopy, multi-angle light scattering and laser Doppler light scattering all suggested that a wide range of starch particle sizes was produced. Some particles were considerably smaller than the original starch granule sizes, but a large proportion appeared to be above several microns in size. The emulsion droplets produced using 1–3 wt.% of starch as emulsifier were quite large (from approximately 1 to 20 μm in diameter), i.e., of the same order of size as a large proportion of the starch particulates. Consequently, the emulsions creamed readily, but they were extremely stable to coalescence with no significant change in the emulsion droplet-size distributions appearing for over 3 months. Further tests on the surface tensions of the homogenized and non-homogenized starch dispersions themselves confirmed the supposition that the O/W emulsions were stabilized by starch particulates and not starch molecules.