Understanding and designing hydrocolloid particles for the stabilisation of foams: a microstructural approach

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Ellis, Amy (2019). Understanding and designing hydrocolloid particles for the stabilisation of foams: a microstructural approach. University of Birmingham. Ph.D.

Ellis2019PhD.pdf
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Abstract

Consumer and Government awareness of obesity related illnesses has progressively increased over the past decade. This has directed the focus of research in the food industry towards healthier product formulations. Aerated products, in particular, are gaining attention, these are often high in fat content as oil droplets provide structural stability as well as desirable sensory attributes. Suspensions of microgel particles, known as fluid gels, have shown promising behaviour in the search for fat replacements as their structures can be designed to mimic those of the fat droplets they are replacing. However, their behaviour when aerated has not yet been explored. Therefore, the ultimate goal of this research is to develop and apply hydrocolloid fluid gel technology to create fat-free aerated products.

The focus of this thesis is directed towards gaining an understanding, on a microstructural level, of the performance of fluid gels in foams, with the aim of designing stable edible foams. Firstly, fluid gel/surfactant systems were characterised and aerated, with a relationship determined between particle microstructure and foam properties. Once aerated, the confinement of particles in foam channels provided localised plugs to drainage. The high volume fraction of particles and their ability to interact resulted in the continuous phase behaving as a network of particles with a finite yield stress. Foam half-life was ultimately dependent upon this; stability considerably increased as the yield stress became larger than the gravitational stress acting inside the foam channels. Yield stress was manipulated by changing the concentration of agar, which increased both the fluid gel particle modulus and volume fraction. This concept was further explored by changing the microstructure through sugar addition. The change in solvent availability affected fluid gel gelation and, subsequently, particle size and material properties. As previously observed in this thesis, foam half-life was ultimately dependent upon fluid gel yield stress. However, at low particle phase volumes, particle size began to directly influence liquid drainage.

In the final chapter, the potential to surface activate kappa carrageenan fluid gel particles was explored. The hydrophobicity of particles was modified by electrostatically binding an ionic surfactant, lauric arginate, onto their surface. Particles subsequently adsorbed at the a/w interface providing enhanced foam stability. The rate of disproportionation and liquid drainage in foams was lowest when an intermediate concentration of surfactant was used, a result of optimum adsorption to bubble interfaces. At high concentrations of surfactant, large aggregates formed which were unable to adsorb to the interface. This modification of kappa carrageenan particles provides a much more versatile ingredient for food microstructure design.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):