The measurement of analyte diffusion from hydrogel microcapsules in model aqueous environments

Model flavor analytes with varying partition coefficients were successfully encapsulated in approximately 150 microm diameter hydrogel microcapsules containing medium chain triglycerides (MCT). Analyte diffusion from the microcapsules into water and dextrose solutions was measured using a UV-VIS spectrophotometer fitted with a fiber optic probe. The diffusion of acetophenone, considered a hydrophilic analyte, was reduced as the dextrose concentration was increased in the water environment. Diffusion comparison was noted as t(1/2) which is the measure of time when 50% of the analyte concentration is released from the microcapsules. The measured t(1/2) for acetophenone in distilled water was 0.40 min. The addition of 20% dextrose to distilled water increased the t(1/2) to 0.60 min while the 40% dextrose addition extended the t(1/2) to 1.4 min. The same t(1/2) trends were also noted with methyl salicylate which is considered a hydrophobic analyte. The measured t(1/2) for methyl salicylate in distilled water was 2.0 min. The addition of 20% dextrose to distilled water increased the t(1/2) to 4.0 min while the 40% dextrose addition extended the t(1/2) to 9.0 min. The addition of dextrose to the water media effectively changes the partitioning media, increasing the resulting partition coefficient (Log P) values. Large changes in the Log P values were confirmed by the GC/FID analysis. In essence, water becomes a poor solvent for the analytes and diffusion is slowed from the hydrophobic MCT contained within the microcapsules as higher concentrations of dextrose is added to the water phase. Since methyl salicylate has a larger Log P(MCT: Water) value compared to acetophenone, the addition of dextrose extends the t(1/2) to a larger extent.