Encapsulation of model actives in fluid gels

The present thesis seeks to extend the knowledge on fluid gel formulations and their potential applications by investigating how these systems can be utilised for the encapsulation of small molecular weight bioactives. This work builds upon previous studies on hydrocolloid-based fluid gels which have shown that these systems can be produced at an industrial scale and can alter food texture. In general, the two main objectives of this research are: - To investigate the encapsulation of bioactives during the production process of alginate fluid gels and to assess the impact of process parameters on the encapsulation and release behaviours of bioactives of/from these materials. - To study the effect of freeze-drying on alginate fluid gels properties and to evaluate this technique for the encapsulation of bioactives in fluid gels particles. In addition, the freeze-drying of these systems was studied as a way to extend the shelf-lives of the encapsulated actives as well as of the whole formulations. This thesis considers first the microstructure and the formation of alginate fluid gels in order to understand the impact of specific formulation constituents (alginate and CaCl2) and processing conditions used during their production, on the final properties of the materials. Small molecular weight model actives were then encapsulated within alginate fluid gels, during their production, confirming that the presence of the actives does not interfere with the alginate fluid gels formation mechanism nor with their final particle dimensions and/or rheological properties. The encapsulation efficiency of all actives was initially very low, but significantly increased upon storage in the case of hydrophobic actives only. The encapsulation mechanism of hydrophobic actives into alginate fluid gel particles was investigated. It was concluded that hydrophobic actives were selectively encapsulated due to the formation of active-matrix hydrophobic interactions that significantly increased upon storage. Release analyses, conducted under sink conditions, revealed that the (hydrophobic) active fraction entrapped within alginate fluid gel particles does not migrate into the used aqueous acceptor phase. Release experiments conducted in simulated gastric fluids revealed the partial release of the fraction of actives encapsulated into alginate fluid gel particles, due to the disruption of the gel network when exposed to acidic conditions. iii Freeze-drying studies of alginate fluid gels were performed and their rehydration revealed that, in general, the properties of these systems, i.e. particle size and rheological behaviour, were not significantly affected by this process. In addition, the encapsulation and release behaviour of actives, loaded in these systems before freeze-drying, were not altered by the drying process. Dried materials showed to be able to extend the shelf-life of both easy-degradable bioactives loaded as well as of the alginate fluid gel matrix, due to water removal. In conclusion, the research presented here promotes current understanding on fluid gel formulations by investigating the use of alginate fluid gels as nano/microcarriers for bioactives. Overall, this work extends the potential applications of hydrocolloid-based fluid gels to include their utilisation for the development of novel encapsulation and release approaches of bioactives relevant to the foods area