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Title: Cocoa particle stabilised emulsions
Author: Gould, Joanne Marie
ISNI:       0000 0004 6423 3751
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2015
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Particle stabilisation of emulsions has generated significant interest in recent years due to the enhanced stability of these emulsions over surfactant or protein stabilised emulsions. Once the particle is at the interface, it is considered to be permanently adsorbed as a high energy input is required to disrupt the particle layers to cause coalescence. The range of food grade particles capable of stabilising emulsions has increased over the last two decades however most food grade particles require a degree of chemical modification. This research introduces the use of cocoa particles as a natural particulate emulsifier stabilising both oil-in-water (o/w) and water-in-oil (w/o) emulsions. The ability of cocoa particles to stabilise o/w emulsions was studied as a function of particle concentration, type, size and continuous phase pH. All emulsions were stable to coalescence for an extended storage period. An overlap in size distribution was found between the emulsion droplets and cocoa particle size, which brought into question the interfacial structure. The role of soluble molecules originating from the cocoa particles and cocoa particle fines in stabilising emulsion droplets were investigated. The fine fraction of cocoa particles was found to be adsorbed at the interface confirming the fact that cocoa particles act as particulate emulsifiers. The origin of the interfacial properties of cocoa particles was investigated using a high fat cocoa powder and cocoa fibre. Cocoa particles were subjected to multiple extraction and hydrolysis protocols, resulting in particles which could and could not stabilise emulsions. The chemical composition and surface properties of the treated particles were investigated to isolate a key component responsible for the interfacial properties of the cocoa particles. The interfacial properties are now known not to lie with the lipid, polyphenol, protein or starch fractions of the cocoa particles. However, no specific component responsible could be identified. The investigations did offer two potential hypotheses as to why cocoa particles stabilise emulsions; the surface roughness and the lignin present in cocoa particles, both of which need further investigation. The enhanced stability of emulsions stabilised by cocoa particles was exploited in an attempt to nutritionally enhance food products. The first application involved the in-vitro digestion of the cocoa particle stabilised emulsions, which showed that the adsorption of cocoa particles at the interface slowed digestion. The benefit of slowing digestion is that undigested material reaches the intestine and activates the ileal brake, which is thought to reduce food intake. In a second study, cocoa particle stabilisation was used to nutritionally improve chocolate by incorporating water into chocolate, using a water-in-cocoa butter emulsion stabilised by cocoa particles. The emulsion chocolates had the gloss and snap expected from chocolate and the emulsion was considered stable due to the homogeneous structure and lack of sugar bloom chocolate. This indicated the potential use of cocoa PSEs in calorie reduced chocolate. This research has highlighted the use of cocoa particles to stabilise food emulsions and the potential advantages of using these particles.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available