Freeze-drying parameters, influence

Influence of Freezing and Freeze-Drying Parameters on Physical Quality Factors 63... 

I have tried to show the interconnection between the property of the product, the goal to make it stable and the necessary processes to achieve this. The problems of the different process steps are discussed with examples and the parameters are described which influence each step. I have avoided following the many theoretical attempts describing one or more of the freeze-drying steps, but have restricted myself to a few equations which permit the calculation of process and product data with sufficient accuracy, or at least, allow an estimate, if some data is mentioned. 

Heinzelmann, K., Franke, K., Velasco, J., and Marquez-Ruiz, G. (2000). Micro-encapsulation of fish oil by freeze-drying techniques and influence of process parameters on oxidative stability during storage. Fur. Food Res. Technol. 211,234 239. 

The stability and suitability of the formulations also needs to be determined, for example, whether the viscosity of the formulation is suitable for the administration route and is stable over time. The water content is a parameter that often has a direct influence on the stability of solid formulations and may influence the appearance of freeze-dried products immensely. Karl-Fisher titration, thermogravitometric analysis (TGA), or DSC is normally used to determine the water content. Various microscopic techniques, where both macroscopic and microscopic appearance of formulation can be determined, such as particle appearance by scanning electron microscopy (SEM) or transmission electron microscopy (TEM), are usually only needed for special formulation. There are several other methods, but which one to choose depends entirely on the formulation and the critical parameters (149,150). 

Moisture content is a very important parameter influencing the stability of dehydrated foods. It has been suggested that the optimal amount of water for long-term storage corresponds in most dehydrated foods to the Brunauer-Emmett-Teller (BET) monolayer value. On the other hand, items such as freeze-dried spinach, cabbage, and orange juice were reported to be more stable at a zero moisture content, whereas items like potatoes and corn had maximum stability at the monomolecular moisture content. It appeared that optimal moisture content could not be predicted with precision on the basis of theoretical considerations. 

A still more special case is the freeze-drying process this process is expensive and therefore worthy of a total cost optimization. Parameters influenced by the properties of the glass container and to be improved are ... 

The diversity of literature data indicates the importance of careful evaluation of the best suitable conditions for freeze drying whereas the freezing conditions, the type and concentration of the cryoprotectant as well as the amount of the lipid nanoparticles are important parameters to consider. Additionally, incorporated drugs may influence stability and redispersion of the freeze dried product and the properties of the dried SLN powder may change during storage due to sintering of the particles. ... 

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