A study of the freeze-drying process in probiotics

Freeze-drying is one of the most common ways to increase the shelf-life of probiotics and pharmaceutics. The Swedish probiotic company BioGaia wanted to follow the freeze-drying process in-situ to understand how the freezing, annealing and drying steps affect the final material structure. To do this they used large-scale infrastructure techniques.

Freeze drying is a very established technique used in the pharmaceutical industry. The established protocols and evaluation methods have been adopted by the probiotics industry. BioGaia wants to investigate whether the probiotic industry’s adoption of the method is optimal. To test this, BioGaia wanted to use controlled methods to change the thickness of the material to find out if thicker materials provide more protection and improve storage stability.

Investigated the structure during freeze-drying

Tomographic imaging techniques, both lab based X-ray microtomography (μCT) and Synchrotron μCT (SRμCT), offer the potential to evaluate the 3D-structure of a freeze-dried product and to follow the evolution of the matrix during freeze-drying. This study utilized a novel in-house designed freeze-drying sample environment designed for μCT at ForMAX beamline at MAX IV Synchrotron to investigate the structure during freeze-drying of a 20% maltodextrin solution and pre-frozen pellets.
SEM contributed immensely to the understanding of the characteristics of freeze-dried structures, both regarding pore-structure as well as material thickness, and ways to alter these factors in a controlled way. The synchrotron radiation X-ray micro computed Tomography (SRμCT) at MAXIV was used, which shortened the scan time from hours to seconds – which made it possible to monitor the dynamics of freeze-drying. Something that will be immensely valuable for the understanding and optimization of a freeze-drying process. 

Thickness an important parameter

The study shows the importance of the material thickness of freeze-dried pellets for the stability of the encapsulated bacteria. Primarily, the storage stability showed a strong correlation with the material thickness. This means that the study found a strong correlation between increased material thickness, so-called encapsulation capacity, and increased storage stability.
This makes material thickness an important parameter for the probiotics industry. Furthermore, the study shows the negative effect of oxygen on storage stability and indicates that thicker materials made of amorphous carbohydrates can hinder the transport of oxygen.