CHARACTERIZING OXYGEN TRANSPORT IN MICROCAPSULES USING A FLUORESCENCE-BASED METHOD

Atisheel Kak

Microencapsulation is a process by which an active ingredient, called a core material, is packaged within a protective matrix, called the wall material(s), in order to prolong the degradation of the core material. Currently, the selection of wall materials for maximizing the shelf-life of encapsulated active ingredients takes a lengthy, iterative, trial-and-error approach. In this process, microcapsules are produced using a wide variety of wall material combinations, the degradation of the core material is monitored for a period of weeks to months, the relative rates of degradation are assessed, and the process is repeated with adjustments made to the wall material composition. In this dissertation, a fluorescence-based method was developed to monitor oxygen transport in microcapsules, in situ, by encapsulating an oxygen-quenching fluorescent dye. The observed decay of fluorescence intensity was related to Fick’s 2nd law for a sphere, whereby a microcapsule-specific effective diffusion coefficient (Deff) was extrapolated. The first study evaluated the effectiveness of this method to distinguish differences in oxygen barrier between microcapsules produced with different materials and dehydration methods. Specifically, this study demonstrated that differences in oxygen barrier can be observed between modified starch and maltodextrins, and between spray-dried and freeze-dried microcapsules. In the second study, the method was applied to select optimal ingredient combinations for industrial formulation development. In particular, the method demonstrated that incorporating low molecular weight trehalose with higher molecular weight carbohydrates in microcapsules can lead to a lower effective rate of oxygen diffusion in the microcapsules. In the third study, the incorporation of cellulose nanofiber (CNF) in microcapsules was assessed by measuring Deff, glass transition temperature, flow properties, and reconstitution properties. Although all of the microcapsules had poor flow and reconstitution properties, CNF imparted a higher oxygen barrier to the microcapsules most likely due to the impermeability of oxygen through the crystalline fractions of CNF. The method developed in this research has demonstrated that the oxygen transfer in microcapsules can be monitored in situ, and the effective oxygen diffusion coefficient of microcapsules can be estimated for a variety of biopolymer combinations for industrial formulation development and characterization of novel oxygen barrier materials.

CHARACTERIZING OXYGEN TRANSPORT IN MICROCAPSULES USING A FLUORESCENCE-BASED METHOD

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