All Freeze dried products are different, they all have a unique transition temperature. For example, if a lyophilized product contains any sugars, salts, buffers, and active ingredients which are dissolved, the interaction of all of these components during freezing determines the threshold above which the product temperature must never exceed during primary drying and most importantly, during the transition between primary and secondary drying. This mixture and the residual moisture in the product also influence risk of supply chain degradation, because residual moisture at higher temperatures can lower the transition temperature of even the dried product during shipment. This effect can transform product that is acceptable before shipment, to be unacceptable upon delivery. The transition temperature of most freeze dried products is not a true eutectic such as sodium chloride and water, which has a transition temperature at about – 21 deg C. Most products contain cryo-protective agents such as sugars, like sucrose, which protect sensitive proteins, it is theorized, by replacing water as it is removed from the molecular structure of the product by sublimation and desorption. Sugars can cause the product to have a wider transition temperature than eutectic compounds. For instance the transition temperature of 5% sucrose solution is from about -33 deg C to -26 deg C. If one approaches or exceeds -26 deg C product temperature during primary drying, the product is at risk of collapse or softening, which may be responsible for shortening the shelf life of the product, interfering with the solubility, and changing the color of the product as the components mobilize and degrade.
If you need expert assistance in transition temperature determination, evaluation of process related parameters as these relate to transition temperature, call upon Applewood Scientific, we can be your resource to assist in determining transition temperatures, developing freeze drying recipes which efficiently dry product retaining the structure, integrity, solubility and efficacy. We will work with your analytical and QC and QA departments on suitable release criteria, for example, and examine and optimize your existing process.