Re-dispersible dry emulsions stabilised with protein polysaccharide conjugates

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Manecka, Gladness-Marry (2020). Re-dispersible dry emulsions stabilised with protein polysaccharide conjugates. University of Birmingham. Ph.D.

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Abstract

Recently the need for more functional food products has opened new fields of research on the subject. Dry emulsions present an opportunity not only for the production of functional ingredients but also for the reduction of industrial costs. However drying emulsions comes with limitations fixed by both the composition of the emulsified product and the drying process used. In the case of reconstitution by rehydration it is important that the emulsified product keep the same textural properties to be a viable commercial product.
The work presented in this thesis investigates the use of promising emulsifiers for the drying and rehydration of emulsions. Maillard conjugates also called glycoconjugates have been used for the production of oil-in-water emulsions. Because of the thicker membrane they form at the oil/water interface, Maillard conjugates are potential candidates for the stabilisation of emulsions destined to be dried. The key challenge when drying complex structures rests in their preservation. The strength and the nature of the interface are two of the parameters that need to be taken into account when attempting to dry an emulsion.
Due to the constant relationship between product formulation and drying process this study proposes a combination of formulation development and process engineering.
To carry out this project conjugates were produced, analysed and tested in model emulsions. Conjugate stabilised oil-in-water emulsions with identical formulation (20% w/w sunflower oil, 80% w/w water) were produced and analysed in different scenarii. Subsequently their ability to be dried and rehydrated was assessed using freeze-drying and spray-drying.
The results showed that the conjugates particle size was highly dependent on the pH of the conjugation reaction. Smaller particle size could be produced without affecting the yield of reaction. The enhanced stability of the systems to external stresses was confirmed. However experiments using a charged polysaccharide showed that at pH close to pKa the stability of the system was challenged.
All emulsions showed good stability to drying at different emulsifier concentrations. The textural components (viscosity and friction coefficient) were well preserved.
The adjustment of the formulation by addition of additives significantly improved the stability of the systems to freeze-drying and spray drying. Overall this study filled some gap of knowledge in the use of Maillard conjugates in oil in-water emulsions. The study of the stability to external stresses such as salt addition or pH modification contributed to the understanding of the functional properties of these conjugates.
Drying and rehydration experiments provided a better understanding of dry emulsions behaviour.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):