Crystal-stabilised edible Pickering emulsions in the presence of ethanol

Ferreira, Ana Claudia (2023). Crystal-stabilised edible Pickering emulsions in the presence of ethanol. University of Birmingham. Ph.D.

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Abstract

With obesity levels growing rapidly over the years there has been an increase in the demand for healthier, more nutritious foods. Nevertheless, the consumers do not want to part with the flavours and textures they have grown to love and expect. For this reason, food engineers have had to develop new formulations and processes that will reduce salt, sugar and fats, as well as deliver key nutrients and vitamins, while maintaining the sensory properties of the food products. One such technique is to create duplex emulsions.
These emulsions, due to their complex structure, offer many possibilities including reduction of sugars, salt and fats, encapsulation of beneficial compounds and targeted delivery of bio composites, among others. However, the same complex structure that gives the duplex emulsion its many advantages also creates a big challenge – how do we stabilise these structures?
There have been many studies and proposed methods on how to create and stabilise duplex emulsions. One method uses fat crystals as stabilisers; this is done by crystallising the fat directly at the interface of the emulsion and allowing them to sinter overtime creating a solid fat “shell” that protects the droplets from destabilisation.
This work will focus on 3 main topics: emulsions containing ethanol, emulsions stabilised with fat crystals and duplex emulsions. The aim is to combine all three to create a stable duplex emulsion stabilised with Pickering fat crystals in the presence of ethanol.
Firstly, the effect of ethanol on simple 2-phase oil-in-water emulsions was investigated. This showed that ethanol has a significant effect, not only on the properties of both phases but also on the stability of the final product. The addition of ethanol to the aqueous phase resulted in a significant decrease of the interfacial tension between the 2 phases. This coupled with the decrease in the density and an increase in the viscosity of the aqueous phase contributed to a decrease in the droplet size of the emulsion and an improvement in the stability of the system (up to 40% ethanol).
Following this, water-in-oil emulsions stabilised with Pickering fat crystals were explored. Various formulations, as well as, process and storage conditions were tested. The combination and concentration of fats, the concentration of the aqueous phase and the concentration of ethanol in the aqueous phase all proved to have an effect on the stability of W/O emulsions. Although the formulations had a clear impact, in this case, the process conditions did not seem to have a significant effect on the stability of the emulsions. Emulsions created with 40/60 (W/O), containing 30% ethanol and stabilised with 1% monostearin and 4% tristearin proved to be stable in the fridge and at room temperature for up to 1 month.
Finally, duplex emulsions stabilised with Pickering fat crystals and containing ethanol were investigated. Although it was possible to create these emulsions, they were only stable when stored in the fridge. To increase their temperature stability it was necessary to increase the number of fat crystals present in the system. This created a challenge when it came to the second emulsification, as the viscosity of the system increased significantly with the addition of more crystals. More work in alternative emulsification methods is necessary to achieve the desired temperature stability in duplex emulsions stabilised with fat crystals and containing ethanol.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):