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Systematic study on DHA-encapsulated particles - droplet drying behavior investigation and product properties optimization
thesisposted on 2017-05-15, 04:34 authored by Wang, Yang
This thesis presents a systematic investigation of the DHA-encapsulated particles. Special research attention was drawn to the particle drying behavior and surface phenomenon during and after the particle formation. As a heat and chemical sensitive substance, DHA is often errapsulated to decrease oxidation or to mask unpleasant taste and odour. Selection of the rest coating materials and micro-encapsulation process technology is crucial. In this study, different shell materials (protein-based and starch-based, respectively) were examined to indicate their feasibility for DHAoil encapsulation and to understand their drying behavior. Spray drying is a primary method to manufacture food and pharmaceutical powders. Before subjecting a new formulation (ingredient or wall material) to this process, informations about drying kinetics and shrinkage parameters, which are crucial to 100del the spray drying process, can be obtained via single-droplet drying experiments. In this study, a glass filament method was adopted to measure the changes in droplet size, weight, and temperature during the drying of emulsion droplets containing DHA at specific solid-liquid ratios under hot air convection. The Reaction Engineering Approach (REA) could then be adopted to describe the drying behavior of the emulsion droplets, and correlate the shrinkage coefficients against the solids content. The heat transfer and mass transfer models of s~cific types of emulsion were also established. The REA model in this thesis has provided an accurate description of drying behaviour of the tested emulsion systems. Significant differerres could be found when comparing the present master curves with previous reJX>rted master curves. The early shell formation process was assumed to be the reason and was confirmed by the further studies. In addition, when an emulsion droplet was dried, the pro~rties of different dissolved solids could lead to different behaviors, for example, different shell formation process. Such phenomena could make droplet drying a very complex process to understand and also would affect the functionality of tre final dried particles. Thus, the surface phenomena of DHA-containing emulsion during convective droplet drying, with the associated functionality changes, were analyzed by the extended glass-filament single droplet drying approach to understand the mechanisms behind these changes. The in situ analysis of particle surface formation allowed changes in the dissolution behavior of tre semi-dried/dried particle to be monitored while droplet drying was in progress. By comparing the changes in dissolution behavior with different shell materials during drying, the possible material migration behavior during the DHA-containing emulsion droplet drying was examined and generated. Discussion based on visual observations of the emulsion morphologies, droplet drying behaviors and dissolution process was presented. The quick crust formation processes of tre DHA-containing emulsion droplets during drying were verified. The surface characterization for DHA containing particle before and after surface oil extraction were also carried out to detect tre influence of different wall materials on the surfa:e formation and surface com}X)sition. The modified-starch showed a better protective property of tre oil than protein. The knowledge developed from this thesis will provide theoretical and technical support for the industrial-scale production of DHA-oil micro-capsule.