Acton and Morris successfully controlled the size of ice crystals in a freeze drying process using the above mentioned principle of power ultrasound. They found that ultrasound irradiation up to 5 s close to the freezing point of sucrose solution resulted into formation of large ice crystals. Conversely, small ice crystals were produced by ultrasound irradiation at greater levels of supercooling, i.e. up to 5 °C below melting point of ice crystals. These authors also confirmed that the application of power ultrasound can fragment the ice crystals which increases the number of nuclei and reduces the size of ice crystals. Kiani et al.