Investigation of Pickering emulsion systems to overcome compositional ripening in reduced-calorie snack-food water-in-oil systems
Creators: name: Tadi, Raj
Publisher: name: The University of Edinburgh
Year: 2024
Subjects: Pickering emulsion systems
compositional ripening
reduced-calorie snack-food
reduced-calorie snack-food water-in-oil systems
Ostwald ripening
water-in oil emulsions
fluorescent confocal microscopy
water-in-dodecane emulsions
Van der Waals force

description: As regulations and consumer desire for healthier dietary options increases, there is a growing interest in producing foods with reduced calorie content. One approach is to replace the high-calorie components with water in the form of water-inoil emulsions. However, food microstructures are metastable and so prone to collapse, resulting in very short lived emulsions with water migrating out of the droplets. This can be due to coalescence, Ostwald ripening, or, if there are other species that can mix with the water, compositional ripening. In the past few decades, particle-stabilised (Pickering) emulsions have garnered great interest due to their unique characteristics. These are due to the interface becoming rigid when stabilised with colloids, as opposed to surfactants, resulting in increased stability against coalescence and Ostwald ripening. This thesis aims to investigate the feasibility of using Pickering emulsions as a solution to the challenge of compositional ripening. To study Pickering emulsions, fluorescent confocal microscopy was utilised to separate and observe the various components. An image analysis pipeline was developed and used with confocal microscopy to track and characterise the evolution of the emulsions over time. As a model Pickering system, water-in-dodecane emulsions stabilised by colloidal particles were initially explored. Similar emulsions were fabricated with various concentrations of sugar in the aqueous phase, and combined with the pure water emulsions. This provided a means of varying the chemical potential difference between the two droplet species, with the water migrating from pure water droplets to sugar-filled ones. To explore the effects of modifying the continuous phase, dodecane was replaced with tributyrin, a short-chain triglyceride found in many foods. In both systems, it was found that the rate of ripening increases with sugar concentrations, with the tributyrin system ripening faster than dodecane, as expected. Interestingly, it was observed that droplets ‘explode’ in dodecane but remain as crumpled states in tributyrin. Evidence that water remains in these crumpled states hints towards a means of overcoming compositional ripening. Following this two further modifications to the model system were investigated. In the first instance, the dodecane system was modified with the addition of toluene once the particles were adsorbed to the interface. The goal of this approach was that the addition of toluene degrades the colloid steric stabiliser, inducing an attractive Van der Waals force between them, creating a more rigid colloidal monolayer. Interestingly, a new end-fate for these droplets was observed, where they slowly fall apart and result in empty broken filaments and sheets. To better understand this behaviour, a recently developed contactless interfacial rheology setup was used to determine the effects of added toluene to the properties of the colloidal interface. In the second instance, the colloid surface chemistry was altered by changing the type of steric stabiliser, inspired by literature indicating differences in the interaction potential for these colloids at oil-water interfaces. Different end states were observed, including crumpled droplets with long-term stability, depending on the size and steric stabilisation of the colloids as well as the aqueous phase they are stabilising.