Abstract: Power ultrasound as an effective way to trigger the initial nucleation of solutions can transform the spontaneous and random process of ice crystal nucleation into a predictable and easy to control one. In this study, the nucleation of catalase solutions with different dissolved oxygen contents was controlled with contact ultrasound before freeze-drying in order to investigate the effect of air injection into the solution on the sublimation drying rate, the porosity and the enzyme activity recovery. The results showed that the sublimation drying time was reduced by 9.36%–41.63% with increasing dissolved oxygen from 4.10 to 13.44 mg/L and the enzyme activity recover was higher than 95% in the dissolved oxygen range of 4.10–10.24 mg/L. The application of controlling crystal nucleation by power ultrasonic with air injection in the vacuum freeze drying of foods and pharmaceuticals is of great significance to shorten the drying time, reduce energy consumption and improve the quality of freeze-dried products.

Key words: power ultrasound, dissolved oxygen content, controlled nucleation, freeze drying, porosity