Effects of different cryoprotectants on microemulsion freeze-drying

In this study, the effects of different cryoprotectants, i.e., mannitol, d -trehalose, lactose, and glycine, were investigated during the evening primrose oil microemulsion freeze-drying process. The glass transition temperature, particle size and dispersion, and appearance of the microemulsions before and after freeze-drying were compared to identify the best cryoprotectant by using differential scanning calorimetry and Dynamic light scattering. In summary, mannitol was shown to be the best cryoprotectant for the evening primrose oil microemulsion due to its high glass transition temperatures, small rehydrated microemulsion particle sizes, uniform particle size distribution, and ability to produce crystal-like freeze-dried powders. Increasing the ratio of cryoprotectant to evening primrose oil generally produced better freeze-dried powders. The optimal mannitol to evening primrose oil ratio for microemulsion freeze-drying was determined to be 6:1.