Encapsulation of caffeine in spray-dried micro-eggs for controlled release: The effect of spray-drying (cooking) temperature

This work has found that the spray-drying temperature affects the microencapsulation and release behaviour of caffeine from spray-dried egg albumen in the form of a powder ("micro-eggs", filled in a gelatine capsule), not in the form of compressed tablets. The spray-dried micro-eggs are more spherical when spray-dried at 60-120 degrees C but are more crumpled when spray-dried at 140-200 degrees C, which is related to the critical denaturation temperature of 56 degrees C for egg albumen. At low inlet temperatures, the particle size of spray-dried micro-eggs and the yield are small while the free moisture content is high. A free moisture content of less than 4.2% is required for high yields. FTIR-ATR (for surface analysis) and Raman (for bulk analysis) spectra indicate greater surface enrichment of protein for higher inlet temperatures. DSC spectra show greater denaturation of protein for the spray-dried micro-eggs produced at higher inlet temperatures, and the spectra also suggest that caffeine is amorphous in the spray-dried micro-eggs. Moreover, the release rate of caffeine has been controlled by changing the inlet temperature. The releases last for 2.5-14 h with inlet temperatures of 60-200 degrees C. The release profiles have been found to fit the first-order, Higuchi, Hixson-Crowell, and Korsmeyer-Peppas release models, well. The release mechanisms of caffeine are suggested to be non-Fickian (more release occurs when the protein matrices are eroded) for the spray-dried micro-eggs produced at low inlet temperatures, whereas Fick's law (corresponding to the molecular diffusion of caffeine) is followed more closely for the spray-dried micro-eggs denatured/cooked at high inlet temperatures, due to the characteristics of the protein shell.