Dissolution Characteristics of Freeze-Dried Pullulan Particles Affected by Solution Concentration and Freezing Medium

Pullulan particles were prepared to improve water solubility. The pullulan droplet with the concentration of 5%, 10%, 15% or 20% (w/w) was injected and frozen in the cryogenic media of liquid nitrogen at −196 °C or cold air at −15 °C, then freeze dried. The results show that most of dried pullulan particles pre-processed in either liquid nitrogen or cold air can be completely dissolved in water within 60 s. The water solubility of as-prepared particles in liquid nitrogen is better than that in cold air. The particles frozen at −196 °C have smaller and more uniform pore structures together with a larger specific surface area than those frozen at −15 °C. It is found that the particles from 10% pullulan solution with liquid nitrogen have largest water solubility and also highest specific surface area (11.78 m²/g).