Submicron O/W emulsions embedded into modified waxy maize starch based matrix: Rheological and microstructural characterization

Abstract

The aim of this study was to investigate the rheological properties and storage stability of submicron O/W emulsions formulated with dried skim milk and vegetable oil at neutral pH, and to analyse the impact of their inclusion into starch suspension. Sunflower oil droplets were pre-emulsified in skim milk suspension by a rotor-stator homogenizer and further an ultrasonic treatment was applied. Droplets sizes decreased after applying ultrasound (US) from 1.4 to 0.4 μm (d32). Emulsions exhibited Bingham flow behaviour and the plastic viscosity increased upon 14 days of storage at 5 °C. Flocculation may be responsible for the increase in viscosity with aging time. Mixed colloidal dispersions (submicron emulsions embedded into starch matrix) showed shear-thinning behaviour. Over storage, light microscope micrographs suggested deposited droplets on the starch granules surface. Flow and viscoelastic behaviour of mixed colloidal dispersions indicated droplets flocculation, attributable to a reversible depletion mechanism of destabilization.